blocks|key|502875|text|这不就是这样的东西吗：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|502876|Textbox+myTxtbx+=+new+Textbox();
myTxtbx.Text+=+"Enter+text+here...";

myTxtbx.GotFocus+%2B=+GotFocus.EventHandle(RemoveText);
myTxtbx.LostFocus+%2B=+LostFocus.EventHandle(AddText);

public+void+RemoveText(object+sender,+EventArgs+e)
{
++++if+(myTxtbx.Text+==+"Enter+text+here...")+
++++{
+++++myTxtbx.Text+=+"";
++++}
}

public+void+AddText(object+sender,+EventArgs+e)
{
++++if+(string.IsNullOrWhiteSpace(myTxtbx.Text))
++++++++myTxtbx.Text+=+"Enter+text+here...";
}|code-block|syntax|javascript|502877|这只是伪代码，但概念是存在的。|502878|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Wouldn't that just be something like this:

<pre><code>Textbox myTxtbx = new Textbox();
myTxtbx.Text = "Enter text here...";

myTxtbx.GotFocus += GotFocus.EventHandle(RemoveText);
myTxtbx.LostFocus += LostFocus.EventHandle(AddText);

public void RemoveText(object sender, EventArgs e)
{
 if (myTxtbx.Text == "Enter text here...") 
 {
 myTxtbx.Text = "";
 }
}

public void AddText(object sender, EventArgs e)
{
 if (string.IsNullOrWhiteSpace(myTxtbx.Text))
 myTxtbx.Text = "Enter text here...";
}
</code></pre>

Thats just pseudocode but the concept is there.

blocks|key|502919|text|您可以使用get+the+default+Template，通过覆盖TextBlock来修改它，并使用Style添加触发器来隐藏和显示它的正确状态。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|502920|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/1559261/control-template-for-existing-controls-in-wpf^0|L|8|Y|9|1F|5|5|O|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

You can <a href="https://stackoverflow.com/questions/1559261/control-template-for-existing-controls-in-wpf">get the default <code>Template</code></a>, modify it by overlaying a <code>TextBlock</code>, and use a <code>Style</code> to add triggers that hide and show it in the right states.

blocks|key|502942|text|你可以使用这个，它对我来说很有效，而且是非常简单的解决方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|502943|++++<Style+x:Key="placeHolder"+TargetType="{x:Type+TextBox}"+BasedOn="{StaticResource+{x:Type+TextBox}}">
++++++++<Setter+Property="Template">
++++++++++++<Setter.Value>
++++++++++++++++<ControlTemplate+TargetType="{x:Type+TextBox}">
++++++++++++++++++++<Grid>
++++++++++++++++++++++++<TextBox+Text="{Binding+Path=Text,
++++++++++++++++++++++++++++++++++++++++++++++++RelativeSource={RelativeSource+TemplatedParent},+
++++++++++++++++++++++++++++++++++++++++++++++++Mode=TwoWay,
++++++++++++++++++++++++++++++++++++++++++++++++UpdateSourceTrigger=PropertyChanged}"
+++++++++++++++++++++++++++++++++x:Name="textSource"+
+++++++++++++++++++++++++++++++++Background="Transparent"+
+++++++++++++++++++++++++++++++++Panel.ZIndex="2"+/>
++++++++++++++++++++++++<TextBox+Text="{TemplateBinding+Tag}"+Background="{TemplateBinding+Background}"+Panel.ZIndex="1">
++++++++++++++++++++++++++++<TextBox.Style>
++++++++++++++++++++++++++++++++<Style+TargetType="{x:Type+TextBox}">
++++++++++++++++++++++++++++++++++++<Setter+Property="Foreground"+Value="Transparent"/>
++++++++++++++++++++++++++++++++++++<Style.Triggers>
++++++++++++++++++++++++++++++++++++++++<DataTrigger+Binding="{Binding+Path=Text,+Source={x:Reference+textSource}}"+Value="">
++++++++++++++++++++++++++++++++++++++++++++<Setter+Property="Foreground"+Value="LightGray"/>
++++++++++++++++++++++++++++++++++++++++</DataTrigger>
++++++++++++++++++++++++++++++++++++</Style.Triggers>
++++++++++++++++++++++++++++++++</Style>
++++++++++++++++++++++++++++</TextBox.Style>
++++++++++++++++++++++++</TextBox>
++++++++++++++++++++</Grid>
++++++++++++++++</ControlTemplate>
++++++++++++</Setter.Value>
++++++++</Setter>
++++</Style>|code-block|syntax|javascript|502944|用法：|502945|<TextBox+Style="{StaticResource+placeHolder}"+Tag="Name+of+customer"+Width="150"+Height="24"/>|502946|‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎|502947|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You can use this, it's working for me and is extremely simple solution.

<pre><code> &lt;Style x:Key="placeHolder" TargetType="{x:Type TextBox}" BasedOn="{StaticResource {x:Type TextBox}}"&gt;
 &lt;Setter Property="Template"&gt;
 &lt;Setter.Value&gt;
 &lt;ControlTemplate TargetType="{x:Type TextBox}"&gt;
 &lt;Grid&gt;
 &lt;TextBox Text="{Binding Path=Text,
 RelativeSource={RelativeSource TemplatedParent}, 
 Mode=TwoWay,
 UpdateSourceTrigger=PropertyChanged}"
 x:Name="textSource" 
 Background="Transparent" 
 Panel.ZIndex="2" /&gt;
 &lt;TextBox Text="{TemplateBinding Tag}" Background="{TemplateBinding Background}" Panel.ZIndex="1"&gt;
 &lt;TextBox.Style&gt;
 &lt;Style TargetType="{x:Type TextBox}"&gt;
 &lt;Setter Property="Foreground" Value="Transparent"/&gt;
 &lt;Style.Triggers&gt;
 &lt;DataTrigger Binding="{Binding Path=Text, Source={x:Reference textSource}}" Value=""&gt;
 &lt;Setter Property="Foreground" Value="LightGray"/&gt;
 &lt;/DataTrigger&gt;
 &lt;/Style.Triggers&gt;
 &lt;/Style&gt;
 &lt;/TextBox.Style&gt;
 &lt;/TextBox&gt;
 &lt;/Grid&gt;
 &lt;/ControlTemplate&gt;
 &lt;/Setter.Value&gt;
 &lt;/Setter&gt;
 &lt;/Style&gt;
</code></pre>

Usage:

<pre><code>&lt;TextBox Style="{StaticResource placeHolder}" Tag="Name of customer" Width="150" Height="24"/&gt;
</code></pre>

‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎

blocks|key|502990|text|我想出了一个对我有效的方法，但这只是因为我愿意使用textbox名称作为我的占位符。见下文。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|502991|public+TextBox+employee+=+new+TextBox();

private+void+InitializeHomeComponent()
{
++++//
++++//employee
++++//
++++this.employee.Name+=+"Caller+Name";
++++this.employee.Text+=+"Caller+Name";
++++this.employee.BackColor+=+System.Drawing.SystemColors.InactiveBorder;
++++this.employee.Location+=+new+System.Drawing.Point(5,+160);
++++this.employee.Size+=+new+System.Drawing.Size(190,+30);
++++this.employee.TabStop+=+false;
++++this.Controls.Add(employee);
++++//+I+loop+through+all+of+my+textboxes+giving+them+the+same+function
++++foreach+(Control+C+in+this.Controls)
++++{
++++++++if+(C.GetType()+==+typeof(System.Windows.Forms.TextBox))
++++++++{
++++++++++++C.GotFocus+%2B=+g_GotFocus;
++++++++++++C.LostFocus+%2B=+g_LostFocus;
++++++++}
+++++}
+}

++++private+void+g_GotFocus(object+sender,+EventArgs+e)
++++{
++++++++var+tbox+=+sender+as+TextBox;
++++++++tbox.Text+=+"";
++++}

++++private+void+g_LostFocus(object+sender,+EventArgs+e)
++++{
++++++++var+tbox+=+sender+as+TextBox;
++++++++if+(tbox.Text+==+"")
++++++++{
++++++++++++tbox.Text+=+tbox.Name;
++++++++}
++++}|code-block|syntax|javascript|502992|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I came up with a method that worked for me, but only because I was willing to use the textbox name as my placeholder. See below.

<pre><code>public TextBox employee = new TextBox();

private void InitializeHomeComponent()
{
 //
 //employee
 //
 this.employee.Name = "Caller Name";
 this.employee.Text = "Caller Name";
 this.employee.BackColor = System.Drawing.SystemColors.InactiveBorder;
 this.employee.Location = new System.Drawing.Point(5, 160);
 this.employee.Size = new System.Drawing.Size(190, 30);
 this.employee.TabStop = false;
 this.Controls.Add(employee);
 // I loop through all of my textboxes giving them the same function
 foreach (Control C in this.Controls)
 {
 if (C.GetType() == typeof(System.Windows.Forms.TextBox))
 {
 C.GotFocus += g_GotFocus;
 C.LostFocus += g_LostFocus;
 }
 }
 }

 private void g_GotFocus(object sender, EventArgs e)
 {
 var tbox = sender as TextBox;
 tbox.Text = "";
 }

 private void g_LostFocus(object sender, EventArgs e)
 {
 var tbox = sender as TextBox;
 if (tbox.Text == "")
 {
 tbox.Text = tbox.Name;
 }
 }
</code></pre>

blocks|key|286337|text|不需要处理焦点进入和焦点离开事件来设置和删除占位符文本，可以使用Windows+SendMessage函数将EM_SETCUEBANNER消息发送到我们的文本框来为我们做这项工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|286338|这可以通过两个简单的步骤来完成。首先，我们需要公开Windows+SendMessage函数。|286339|private+const+int+EM_SETCUEBANNER+=+0x1501;

[DllImport("user32.dll",+CharSet+=+CharSet.Auto)]
private+static+extern+Int32+SendMessage(IntPtr+hWnd,+int+msg,+int+wParam,+[MarshalAs(UnmanagedType.LPWStr)]string+lParam);|code-block|syntax|javascript|286340|然后，只需使用textbox的句柄、EM_SETCUEBANNER的值和我们想要设置的文本来调用该方法。|286341|SendMessage(textBox1.Handle,+EM_SETCUEBANNER,+0,+"Username");
SendMessage(textBox2.Handle,+EM_SETCUEBANNER,+0,+"Password");|286342|参考：Set+placeholder+text+for+textbox+(cue+text)|286343|entityMap|0|LINK|mutability|MUTABLE|url|http://www.fluxbytes.com/csharp/set-placeholder-text-for-textbox-cue-text/^0|1I|F|0|X|B|0|0|0|0|3|17|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|16|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|17|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|19|8|@]|D|@$9|1A|A|1B|1|1C]]|E|$]]|$1|S|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

Instead of handling the focus enter and focus leave events in order to set and remove the placeholder text it is possible to use the Windows SendMessage function to send <code>EM_SETCUEBANNER</code> message to our textbox to do the work for us.

This can be done with two easy steps. First we need to expose the Windows <code>SendMessage</code> function.

<pre><code>private const int EM_SETCUEBANNER = 0x1501;

[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern Int32 SendMessage(IntPtr hWnd, int msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)]string lParam);
</code></pre>

Then simply call the method with the handle of our textbox, EM_SETCUEBANNER’s value and the text we want to set.

<pre><code>SendMessage(textBox1.Handle, EM_SETCUEBANNER, 0, "Username");
SendMessage(textBox2.Handle, EM_SETCUEBANNER, 0, "Password");
</code></pre>

Reference: <a href="http://www.fluxbytes.com/csharp/set-placeholder-text-for-textbox-cue-text/" rel="noreferrer">Set placeholder text for textbox (cue text)</a>

blocks|key|286359|text|尝试以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286360|<TextBox+x:Name="InvoiceDate"+Text=""+Width="300"++TextAlignment="Left"+Height="30"+Grid.Row="0"+Grid.Column="3"+Grid.ColumnSpan="2"+/>
++++++++++++++++++++<TextBlock+IsHitTestVisible="False"+Text="Men+att+läsa"+Width="300"++TextAlignment="Left"+Height="30"+Grid.Row="0"+Grid.Column="3"+Grid.ColumnSpan="2"+Padding="5,+5,+5,+5"++Foreground="LightGray">
++++++++++++++++++++++++<TextBlock.Style>
++++++++++++++++++++++++++++<Style+TargetType="{x:Type+TextBlock}">
++++++++++++++++++++++++++++++++<Setter+Property="Visibility"+Value="Collapsed"/>
++++++++++++++++++++++++++++++++<Style.Triggers>
++++++++++++++++++++++++++++++++++++<DataTrigger+Binding="{Binding+Text,+ElementName=InvoiceDate}"+Value="">
++++++++++++++++++++++++++++++++++++++++<Setter+Property="Visibility"+Value="Visible"/>
++++++++++++++++++++++++++++++++++++</DataTrigger>
++++++++++++++++++++++++++++++++++++<DataTrigger+Binding="{Binding+ElementName=InvoiceDate,+Path=IsFocused}"+Value="True">
++++++++++++++++++++++++++++++++++++++++<Setter+Property="Visibility"+Value="Collapsed"/>
++++++++++++++++++++++++++++++++++++</DataTrigger>

++++++++++++++++++++++++++++++++</Style.Triggers>
++++++++++++++++++++++++++++</Style>
++++++++++++++++++++++++</TextBlock.Style>
++++++++++++++++++++</TextBlock>|code-block|syntax|javascript|286361|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try the following code:

<pre><code>&lt;TextBox x:Name="InvoiceDate" Text="" Width="300" TextAlignment="Left" Height="30" Grid.Row="0" Grid.Column="3" Grid.ColumnSpan="2" /&gt;
 &lt;TextBlock IsHitTestVisible="False" Text="Men att läsa" Width="300" TextAlignment="Left" Height="30" Grid.Row="0" Grid.Column="3" Grid.ColumnSpan="2" Padding="5, 5, 5, 5" Foreground="LightGray"&gt;
 &lt;TextBlock.Style&gt;
 &lt;Style TargetType="{x:Type TextBlock}"&gt;
 &lt;Setter Property="Visibility" Value="Collapsed"/&gt;
 &lt;Style.Triggers&gt;
 &lt;DataTrigger Binding="{Binding Text, ElementName=InvoiceDate}" Value=""&gt;
 &lt;Setter Property="Visibility" Value="Visible"/&gt;
 &lt;/DataTrigger&gt;
 &lt;DataTrigger Binding="{Binding ElementName=InvoiceDate, Path=IsFocused}" Value="True"&gt;
 &lt;Setter Property="Visibility" Value="Collapsed"/&gt;
 &lt;/DataTrigger&gt;

 &lt;/Style.Triggers&gt;
 &lt;/Style&gt;
 &lt;/TextBlock.Style&gt;
 &lt;/TextBlock&gt;
</code></pre>

blocks|key|503117|text|您也可以在鼠标单击时执行此操作，假设您的占位符文本为"User_Name“|type|unstyled|depth|inlineStyleRanges|entityRanges|data|503118|+private+void+textBox1_MouseClick(object+sender,+MouseEventArgs+e)
+{
+++++if(textBox1.Text+==+"User_Name")
++++++++++textBox1.Text+=+"";
+}|code-block|syntax|javascript|503119|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

you can also do that when the mouse clicks, let's suppose your placeholder text is "User_Name"

<pre><code> private void textBox1_MouseClick(object sender, MouseEventArgs e)
 {
 if(textBox1.Text == "User_Name")
 textBox1.Text = "";
 }
</code></pre>

blocks|key|286468|text|这意味着你有一个按钮，它允许你做一个动作，比如登录或其他什么。在执行此操作之前，请检查文本框是否已填充。如果不是，它将替换文本|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286469|+private+void+button_Click(object+sender,+EventArgs+e)
+{
+++++string+textBoxText+=+textBox.Text;

+++++if+(String.IsNullOrWhiteSpace(textBoxText))
+++++{
+++++++++textBox.Text+=+"Fill+in+the+textbox";
+++++}
+}

+private+void+textBox_Enter(object+sender,+EventArgs+e)
+{
+++++TextBox+currentTextbox+=+sender+as+TextBox;
+++++if+(currentTextbox.Text+==+"Fill+in+the+textbox")
+++++{
+++++++++currentTextbox.Text+=+"";
+++++}
+}|code-block|syntax|javascript|286470|这有点俗气，但检查文本中你给出的值是我能做的最好的自动取款机，在c#方面不是很好，以获得更好的解决方案。|286471|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

This would mean you have a button which allows you to do an action, such as logging in or something. Before you do the action you check if the textbox is filled in. If not it will replace the text

<pre><code> private void button_Click(object sender, EventArgs e)
 {
 string textBoxText = textBox.Text;

 if (String.IsNullOrWhiteSpace(textBoxText))
 {
 textBox.Text = "Fill in the textbox";
 }
 }

 private void textBox_Enter(object sender, EventArgs e)
 {
 TextBox currentTextbox = sender as TextBox;
 if (currentTextbox.Text == "Fill in the textbox")
 {
 currentTextbox.Text = "";
 }
 }
</code></pre>

It's kind of cheesy but checking the text for the value you're giving it is the best I can do atm, not that good at c# to get a better solution.

blocks|key|286510|text|txtUsuario.Attributes.Add("placeholder"，"Texto")；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286511|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

txtUsuario.Attributes.Add("placeholder", "Texto");

blocks|key|286519|text|这不是我的代码，但我经常使用它，它工作得很完美……仅XAML|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286520|<TextBox+x:Name="Textbox"+Height="23"+Margin="0,17,18.8,0"+TextWrapping="Wrap"+Text=""+VerticalAlignment="Top"+HorizontalAlignment="Right"+></TextBox>

<TextBlock+x:Name="Placeholder"+IsHitTestVisible="False"+TextWrapping="Wrap"+Text="Placeholder+Text"+VerticalAlignment="Top"+Margin="0,20,298.8,0"+Foreground="DarkGray"+HorizontalAlignment="Right"+Width="214">
++<TextBlock.Style>
++++<Style+TargetType="{x:Type+TextBlock}">
++++++<Setter+Property="Visibility"+Value="Collapsed"/>
++++++<Style.Triggers>
++++++++<DataTrigger+Binding="{Binding+Text,+ElementName=Textbox}"+Value="">
++++++++++<Setter+Property="Visibility"+Value="Visible"/>
++++++++</DataTrigger>
++++++</Style.Triggers>
++++</Style>
++</TextBlock.Style>
</TextBlock>|code-block|syntax|javascript|286521|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is not my code, but I use it a lot and it works perfect... XAML ONLY

<pre><code>&lt;TextBox x:Name="Textbox" Height="23" Margin="0,17,18.8,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" HorizontalAlignment="Right" &gt;&lt;/TextBox&gt;

&lt;TextBlock x:Name="Placeholder" IsHitTestVisible="False" TextWrapping="Wrap" Text="Placeholder Text" VerticalAlignment="Top" Margin="0,20,298.8,0" Foreground="DarkGray" HorizontalAlignment="Right" Width="214"&gt;
 &lt;TextBlock.Style&gt;
 &lt;Style TargetType="{x:Type TextBlock}"&gt;
 &lt;Setter Property="Visibility" Value="Collapsed"/&gt;
 &lt;Style.Triggers&gt;
 &lt;DataTrigger Binding="{Binding Text, ElementName=Textbox}" Value=""&gt;
 &lt;Setter Property="Visibility" Value="Visible"/&gt;
 &lt;/DataTrigger&gt;
 &lt;/Style.Triggers&gt;
 &lt;/Style&gt;
 &lt;/TextBlock.Style&gt;
&lt;/TextBlock&gt;
</code></pre>

blocks|key|503278|text|++++public+void+Initialize()
++++{
++++++++SetPlaceHolder(loginTextBox,+"+Логин+");
++++++++SetPlaceHolder(passwordTextBox,+"+Пароль+");
++++}

++++public+void+SetPlaceHolder(Control+control,+string+PlaceHolderText)
++++{
++++++++control.Text+=+PlaceHolderText;
++++++++control.GotFocus+%2B=+delegate(object+sender,+EventArgs+args)+{
++++++++++++if+(control.Text+==+PlaceHolderText)
++++++++++++{
++++++++++++++++control.Text+=+"";
++++++++++++}
++++++++};
++++++++control.LostFocus+%2B=+delegate(object+sender,+EventArgs+args){
++++++++++++if+(control.Text.Length+==+0)
++++++++++++{
++++++++++++++++control.Text+=+PlaceHolderText;
++++++++++++}
++++++++};
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|503279|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code> public void Initialize()
 {
 SetPlaceHolder(loginTextBox, " Логин ");
 SetPlaceHolder(passwordTextBox, " Пароль ");
 }

 public void SetPlaceHolder(Control control, string PlaceHolderText)
 {
 control.Text = PlaceHolderText;
 control.GotFocus += delegate(object sender, EventArgs args) {
 if (control.Text == PlaceHolderText)
 {
 control.Text = "";
 }
 };
 control.LostFocus += delegate(object sender, EventArgs args){
 if (control.Text.Length == 0)
 {
 control.Text = PlaceHolderText;
 }
 };
 }
</code></pre>

blocks|key|286571|text|用于救援的附加属性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286572|public+static+class+TextboxExtensions
{
++++public+static+readonly+DependencyProperty+PlaceholderProperty+=+
++++++++DependencyProperty.RegisterAttached(
++++++++++++"Placeholder",+
++++++++++++typeof(string),+
++++++++++++typeof(TextboxExtensions),+
++++++++++++new+PropertyMetadata(default(string),+propertyChangedCallback:+PlaceholderChanged)
++++++++++++);

++++private+static+void+PlaceholderChanged(DependencyObject+dependencyObject,+DependencyPropertyChangedEventArgs+args)
++++{
++++++++var+tb+=+dependencyObject+as+TextBox;

++++++++if+(tb+==+null)
++++++++++++return;

++++++++tb.LostFocus+-=+OnLostFocus;
++++++++tb.GotFocus+-=+OnGotFocus;

++++++++if+(args.NewValue+!=+null)
++++++++{
++++++++++++tb.GotFocus+%2B=+OnGotFocus;
++++++++++++tb.LostFocus+%2B=+OnLostFocus;
++++++++}

++++++++SetPlaceholder(dependencyObject,+args.NewValue+as+string);

++++++++if+(!tb.IsFocused)
++++++++++++ShowPlaceholder(tb);
++++}

++++private+static+void+OnLostFocus(object+sender,+RoutedEventArgs+routedEventArgs)
++++{
++++++++ShowPlaceholder(sender+as+TextBox);
++++}

++++private+static+void+OnGotFocus(object+sender,+RoutedEventArgs+routedEventArgs)
++++{
++++++++HidePlaceholder(sender+as+TextBox);
++++}

++++[AttachedPropertyBrowsableForType(typeof(TextBox))]
++++public+static+void+SetPlaceholder(DependencyObject+element,+string+value)
++++{
++++++++element.SetValue(PlaceholderProperty,+value);
++++}

++++[AttachedPropertyBrowsableForType(typeof(TextBox))]
++++public+static+string+GetPlaceholder(DependencyObject+element)
++++{
++++++++return+(string)element.GetValue(PlaceholderProperty);
++++}

++++private+static+void+ShowPlaceholder(TextBox+textBox)
++++{
++++++++if+(string.IsNullOrWhiteSpace(textBox.Text))
++++++++{
++++++++++++textBox.Text+=+GetPlaceholder(textBox);
++++++++}
++++}

++++private+static+void+HidePlaceholder(TextBox+textBox)
++++{
++++++++string+placeholderText+=+GetPlaceholder(textBox);

++++++++if+(textBox.Text+==+placeholderText)
++++++++++++textBox.Text+=+string.Empty;
++++}
}|code-block|syntax|javascript|286573|用法：|286574|<TextBox+Text="hi"+local:TextboxExtensions.Placeholder="Hello+there"></TextBox>|286575|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Attached properties to the rescue:

<pre><code>public static class TextboxExtensions
{
 public static readonly DependencyProperty PlaceholderProperty = 
 DependencyProperty.RegisterAttached(
 "Placeholder", 
 typeof(string), 
 typeof(TextboxExtensions), 
 new PropertyMetadata(default(string), propertyChangedCallback: PlaceholderChanged)
 );

 private static void PlaceholderChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args)
 {
 var tb = dependencyObject as TextBox;

 if (tb == null)
 return;

 tb.LostFocus -= OnLostFocus;
 tb.GotFocus -= OnGotFocus;

 if (args.NewValue != null)
 {
 tb.GotFocus += OnGotFocus;
 tb.LostFocus += OnLostFocus;
 }

 SetPlaceholder(dependencyObject, args.NewValue as string);

 if (!tb.IsFocused)
 ShowPlaceholder(tb);
 }

 private static void OnLostFocus(object sender, RoutedEventArgs routedEventArgs)
 {
 ShowPlaceholder(sender as TextBox);
 }

 private static void OnGotFocus(object sender, RoutedEventArgs routedEventArgs)
 {
 HidePlaceholder(sender as TextBox);
 }

 [AttachedPropertyBrowsableForType(typeof(TextBox))]
 public static void SetPlaceholder(DependencyObject element, string value)
 {
 element.SetValue(PlaceholderProperty, value);
 }

 [AttachedPropertyBrowsableForType(typeof(TextBox))]
 public static string GetPlaceholder(DependencyObject element)
 {
 return (string)element.GetValue(PlaceholderProperty);
 }

 private static void ShowPlaceholder(TextBox textBox)
 {
 if (string.IsNullOrWhiteSpace(textBox.Text))
 {
 textBox.Text = GetPlaceholder(textBox);
 }
 }

 private static void HidePlaceholder(TextBox textBox)
 {
 string placeholderText = GetPlaceholder(textBox);

 if (textBox.Text == placeholderText)
 textBox.Text = string.Empty;
 }
}
</code></pre>

Usage: 

<pre><code>&lt;TextBox Text="hi" local:TextboxExtensions.Placeholder="Hello there"&gt;&lt;/TextBox&gt;
</code></pre>

blocks|key|286670|text|将此类添加到您的项目并生成您的解决方案。单击visual+studio上的“工具箱”，您将看到一个名为PlaceholderTextBox的新textbox组件。在表单设计中删除当前的文本框并替换为PlaceHolderTextBox。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286671|​|286672|📷|atomic|offset|length|286673|286674|PlaceHolderTextBox有一个属性PlaceHolderText。设置您想要的任何文本并祝您愉快:)|286675|public+class+PlaceHolderTextBox+:+TextBox
{

++++bool+isPlaceHolder+=+true;
++++string+_placeHolderText;
++++public+string+PlaceHolderText
++++{
++++++++get+{+return+_placeHolderText;+}
++++++++set
++++++++{
++++++++++++_placeHolderText+=+value;
++++++++++++setPlaceholder();
++++++++}
++++}

++++public+new+string+Text
++++{
++++++++get+=>+isPlaceHolder+?+string.Empty+:+base.Text;
++++++++set+=>+base.Text+=+value;
++++}

++++//when+the+control+loses+focus,+the+placeholder+is+shown
++++private+void+setPlaceholder()
++++{
++++++++if+(string.IsNullOrEmpty(base.Text))
++++++++{
++++++++++++base.Text+=+PlaceHolderText;
++++++++++++this.ForeColor+=+Color.Gray;
++++++++++++this.Font+=+new+Font(this.Font,+FontStyle.Italic);
++++++++++++isPlaceHolder+=+true;
++++++++}
++++}

++++//when+the+control+is+focused,+the+placeholder+is+removed
++++private+void+removePlaceHolder()
++++{

++++++++if+(isPlaceHolder)
++++++++{
++++++++++++base.Text+=+"";
++++++++++++this.ForeColor+=+System.Drawing.SystemColors.WindowText;
++++++++++++this.Font+=+new+Font(this.Font,+FontStyle.Regular);
++++++++++++isPlaceHolder+=+false;
++++++++}
++++}
++++public+PlaceHolderTextBox()
++++{
++++++++GotFocus+%2B=+removePlaceHolder;
++++++++LostFocus+%2B=+setPlaceholder;
++++}

++++private+void+setPlaceholder(object+sender,+EventArgs+e)
++++{
++++++++setPlaceholder();
++++}

++++private+void+removePlaceHolder(object+sender,+EventArgs+e)
++++{
++++++++removePlaceHolder();
++++}
}|code-block|syntax|javascript|286676|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/87cdc2941ad61faed60ae15f6e624b56.png|imageAlt^0|0|0|0|1|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|10|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|11|8|@]|9|@$G|12|H|13|1|14]]|A|$]]|$1|I|3|C|5|6|7|15|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|16|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|17|8|@]|9|@]|A|$O|P]]|$1|Q|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X|Y|-4]]]]

Add this class your project and build your solution. Click to Toolbox on visual studio you will see a new textbox component named PlaceholderTextBox. Delete your current textbox on form designe and replace with PlaceHolderTextBox.

<a href="https://i.stack.imgur.com/BZJd4.png" rel="noreferrer"><img src="https://i.stack.imgur.com/BZJd4.png" alt="enter image description here"></a>

PlaceHolderTextBox has a property PlaceHolderText. Set any text you want and have nice day :)

<pre><code>public class PlaceHolderTextBox : TextBox
{

 bool isPlaceHolder = true;
 string _placeHolderText;
 public string PlaceHolderText
 {
 get { return _placeHolderText; }
 set
 {
 _placeHolderText = value;
 setPlaceholder();
 }
 }

 public new string Text
 {
 get =&gt; isPlaceHolder ? string.Empty : base.Text;
 set =&gt; base.Text = value;
 }

 //when the control loses focus, the placeholder is shown
 private void setPlaceholder()
 {
 if (string.IsNullOrEmpty(base.Text))
 {
 base.Text = PlaceHolderText;
 this.ForeColor = Color.Gray;
 this.Font = new Font(this.Font, FontStyle.Italic);
 isPlaceHolder = true;
 }
 }

 //when the control is focused, the placeholder is removed
 private void removePlaceHolder()
 {

 if (isPlaceHolder)
 {
 base.Text = "";
 this.ForeColor = System.Drawing.SystemColors.WindowText;
 this.Font = new Font(this.Font, FontStyle.Regular);
 isPlaceHolder = false;
 }
 }
 public PlaceHolderTextBox()
 {
 GotFocus += removePlaceHolder;
 LostFocus += setPlaceholder;
 }

 private void setPlaceholder(object sender, EventArgs e)
 {
 setPlaceholder();
 }

 private void removePlaceHolder(object sender, EventArgs e)
 {
 removePlaceHolder();
 }
}
</code></pre>

blocks|key|286720|text|基于ExceptionLimeCat的回答，一个改进：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286721|Color+farbe;
string+ph+=+"Placeholder-Text";

private+void+Form1_Load(object+sender,+EventArgs+e)
{
++++farbe+=+myTxtbx.ForeColor;
++++myTxtbx.GotFocus+%2B=+RemoveText;
++++myTxtbx.LostFocus+%2B=+AddText;
++++myTxtbx.Text+=+ph;
}


public+void+RemoveText(object+sender,+EventArgs+e)
{
++++myTxtbx.ForeColor+=+farbe;
++++if+(myTxtbx.Text+==+ph)
++++++++myTxtbx.Text+=+"";
}

public+void+AddText(object+sender,+EventArgs+e)
{
++++if+(String.IsNullOrWhiteSpace(myTxtbx.Text))
++++{
++++++++myTxtbx.ForeColor+=+Color.Gray;
++++++++myTxtbx.Text+=+ph;
++++}
}|code-block|syntax|javascript|286722|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Based on ExceptionLimeCat's answer, an improvement:

<pre><code>Color farbe;
string ph = "Placeholder-Text";

private void Form1_Load(object sender, EventArgs e)
{
 farbe = myTxtbx.ForeColor;
 myTxtbx.GotFocus += RemoveText;
 myTxtbx.LostFocus += AddText;
 myTxtbx.Text = ph;
}


public void RemoveText(object sender, EventArgs e)
{
 myTxtbx.ForeColor = farbe;
 if (myTxtbx.Text == ph)
 myTxtbx.Text = "";
}

public void AddText(object sender, EventArgs e)
{
 if (String.IsNullOrWhiteSpace(myTxtbx.Text))
 {
 myTxtbx.ForeColor = Color.Gray;
 myTxtbx.Text = ph;
 }
}
</code></pre>

blocks|key|286822|text|我没有使用TextBox的.Text属性，而是用占位符覆盖了TextBlock。我无法使用.Text属性，因为它已绑定到事件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|286823|XAML：|286824|<Canvas+Name="placeHolderCanvas">
++++<TextBox++AcceptsReturn="True"+Name="txtAddress"+Height="50"+Width="{Binding+ActualWidth,+ElementName=placeHolderCanvas}"
++++++++++++++Tag="Please+enter+your+address"/>
</Canvas>|code-block|syntax|javascript|286825|VB.NET|286826|Public+Shared+Sub+InitPlaceholder(canvas+As+Canvas)
++++Dim+txt+As+TextBox+=+canvas.Children.OfType(Of+TextBox).First()
++++Dim+placeHolderLabel+=+New+TextBlock()+With+{.Text+=+txt.Tag,
+++++++++++++++++++++++++++++++++++++++++++++++++.Foreground+=+New+SolidColorBrush(Color.FromRgb(&H77,+&H77,+&H77)),
+++++++++++++++++++++++++++++++++++++++++++++++++.IsHitTestVisible+=+False}
++++Canvas.SetLeft(placeHolderLabel,+3)
++++Canvas.SetTop(placeHolderLabel,+1)
++++canvas.Children.Add(placeHolderLabel)
++++AddHandler+txt.TextChanged,+Sub()+placeHolderLabel.Visibility+=+If(txt.Text+=+"",+Visibility.Visible,+Visibility.Hidden)
End+Sub|286827|结果：|286828|📷|atomic|offset|length|286829|​|286830|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/774062321b2cc23b57b84039b4974f72.png|imageAlt^0|0|0|0|0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|15|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|17|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|19|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|1A|8|@]|9|@$R|1B|S|1C|1|1D]]|A|$]]|$1|T|3|U|5|6|7|1E|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]]|W|$X|$5|Y|Z|10|A|$11|12|13|-4]]]]

Instead of using the .Text property of a TextBox, I overlayed a TextBlock with the placeholder.
I couldn't use the .Text property because this was binded to an Event.

XAML:

<pre><code>&lt;Canvas Name="placeHolderCanvas"&gt;
 &lt;TextBox AcceptsReturn="True" Name="txtAddress" Height="50" Width="{Binding ActualWidth, ElementName=placeHolderCanvas}"
 Tag="Please enter your address"/&gt;
&lt;/Canvas&gt;
</code></pre>

VB.NET

<pre><code>Public Shared Sub InitPlaceholder(canvas As Canvas)
 Dim txt As TextBox = canvas.Children.OfType(Of TextBox).First()
 Dim placeHolderLabel = New TextBlock() With {.Text = txt.Tag,
 .Foreground = New SolidColorBrush(Color.FromRgb(&amp;H77, &amp;H77, &amp;H77)),
 .IsHitTestVisible = False}
 Canvas.SetLeft(placeHolderLabel, 3)
 Canvas.SetTop(placeHolderLabel, 1)
 canvas.Children.Add(placeHolderLabel)
 AddHandler txt.TextChanged, Sub() placeHolderLabel.Visibility = If(txt.Text = "", Visibility.Visible, Visibility.Hidden)
End Sub
</code></pre>

Result:
<a href="https://i.stack.imgur.com/6KVSs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6KVSs.png" alt="enter image description here"></a>

blocks|key|286876|text|虽然使用EM_SETCUEBANNER消息可能是最简单的，但我不喜欢的一件事是，当控件获得焦点时，占位符文本会消失。当我填写表格时，这是我最恼火的地方。我必须关闭它才能记住该字段的用途。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|286877|因此，这是WinForms的另一个解决方案。它覆盖了控件顶部的Label，只有当用户开始键入时，该控件才会消失。|286878|它肯定不是防弹的。它接受任何Control，但我只用TextBox测试过。它可能需要修改才能与某些控件一起使用。该方法返回Label控件，以防您在特定情况下需要对其进行一些修改，但这可能永远不需要。|286879|像这样使用它：|286880|SetPlaceholder(txtSearch,+"Type+what+you're+searching+for");|code-block|syntax|javascript|286881|下面是方法：|286882|///+<summary>
///+Sets+placeholder+text+on+a+control+(may+not+work+for+some+controls)
///+</summary>
///+<param+name="control">The+control+to+set+the+placeholder+on</param>
///+<param+name="text">The+text+to+display+as+the+placeholder</param>
///+<returns>The+newly-created+placeholder+Label</returns>
public+static+Label+SetPlaceholder(Control+control,+string+text)+{
++++var+placeholder+=+new+Label+{
++++++++Text+=+text,
++++++++Font+=+control.Font,
++++++++ForeColor+=+Color.Gray,
++++++++BackColor+=+Color.Transparent,
++++++++Cursor+=+Cursors.IBeam,
++++++++Margin+=+Padding.Empty,

++++++++//get+rid+of+the+left+margin+that+all+labels+have
++++++++FlatStyle+=+FlatStyle.System,
++++++++AutoSize+=+false,

++++++++//Leave+1px+on+the+left+so+we+can+see+the+blinking+cursor
++++++++Size+=+new+Size(control.Size.Width+-+1,+control.Size.Height),
++++++++Location+=+new+Point(control.Location.X+%2B+1,+control.Location.Y)
++++};

++++//when+clicking+on+the+label,+pass+focus+to+the+control
++++placeholder.Click+%2B=+(sender,+args)+=>+{+control.Focus();+};

++++//disappear+when+the+user+starts+typing
++++control.TextChanged+%2B=+(sender,+args)+=>+{
++++++++placeholder.Visible+=+string.IsNullOrEmpty(control.Text);
++++};

++++//stay+the+same+size/location+as+the+control
++++EventHandler+updateSize+=+(sender,+args)+=>+{
++++++++placeholder.Location+=+new+Point(control.Location.X+%2B+1,+control.Location.Y);
++++++++placeholder.Size+=+new+Size(control.Size.Width+-+1,+control.Size.Height);
++++};

++++control.SizeChanged+%2B=+updateSize;
++++control.LocationChanged+%2B=+updateSize;

++++control.Parent.Controls.Add(placeholder);
++++placeholder.BringToFront();

++++return+placeholder;
}|286883|entityMap^0|4|F|0|V|5|0|E|7|Q|7|1P|5|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|19|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1A|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1B|8|@]|D|@]|E|$]]|$1|S|3|T|5|N|7|1C|8|@]|D|@]|E|$O|P]]|$1|U|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|V|$]]

While using the <code>EM_SETCUEBANNER</code> message is probably simplest, one thing I do not like is that the placeholder text disappears when the control gets focus. That's a pet peeve of mine when I'm filling out forms. I have to click off of it to remember what the field is for.

So here is another solution for WinForms. It overlays a <code>Label</code> on top of the control, which disappears only when the user starts typing.

It's certainly not bulletproof. It accepts any <code>Control</code>, but I've only tested with a <code>TextBox</code>. It may need modification to work with some controls. The method returns the <code>Label</code> control in case you need to modify it a bit in a specific case, but that may never be needed.

Use it like this:

<pre><code>SetPlaceholder(txtSearch, "Type what you're searching for");
</code></pre>

Here is the method:

<pre><code>/// &lt;summary&gt;
/// Sets placeholder text on a control (may not work for some controls)
/// &lt;/summary&gt;
/// &lt;param name="control"&gt;The control to set the placeholder on&lt;/param&gt;
/// &lt;param name="text"&gt;The text to display as the placeholder&lt;/param&gt;
/// &lt;returns&gt;The newly-created placeholder Label&lt;/returns&gt;
public static Label SetPlaceholder(Control control, string text) {
 var placeholder = new Label {
 Text = text,
 Font = control.Font,
 ForeColor = Color.Gray,
 BackColor = Color.Transparent,
 Cursor = Cursors.IBeam,
 Margin = Padding.Empty,

 //get rid of the left margin that all labels have
 FlatStyle = FlatStyle.System,
 AutoSize = false,

 //Leave 1px on the left so we can see the blinking cursor
 Size = new Size(control.Size.Width - 1, control.Size.Height),
 Location = new Point(control.Location.X + 1, control.Location.Y)
 };

 //when clicking on the label, pass focus to the control
 placeholder.Click += (sender, args) =&gt; { control.Focus(); };

 //disappear when the user starts typing
 control.TextChanged += (sender, args) =&gt; {
 placeholder.Visible = string.IsNullOrEmpty(control.Text);
 };

 //stay the same size/location as the control
 EventHandler updateSize = (sender, args) =&gt; {
 placeholder.Location = new Point(control.Location.X + 1, control.Location.Y);
 placeholder.Size = new Size(control.Size.Width - 1, control.Size.Height);
 };

 control.SizeChanged += updateSize;
 control.LocationChanged += updateSize;

 control.Parent.Controls.Add(placeholder);
 placeholder.BringToFront();

 return placeholder;
}
</code></pre>

blocks|key|503647|text|using+System;
using+System.Collections.Generic;
using+System.Linq;
using+System.Text;
using+System.Windows;
using+System.Windows.Controls;

namespace+App_name
{
+++public+class+CustomTextBox+:+TextBox
++++{
++++++++private+string+Text_+=+"";
++++++++public+CustomTextBox()+:+base()
++++++++{}

++++++++public+string+setHint
++++++++{
++++++++++++get+{+return+Text_;+}
++++++++++++set+{+Text_+=+value;+}
++++++++}
++++++++protected+override+void+OnGotFocus(RoutedEventArgs+e)
++++++++{
++++++++++++base.OnGotFocus(e);
++++++++++++if+(Text_.Equals(this.Text))
++++++++++++++++this.Clear();
++++++++}
++++++++protected+override+void+OnLostFocus(RoutedEventArgs+e)
++++++++{
++++++++++++base.OnLostFocus(e);
++++++++++++if+(String.IsNullOrWhiteSpace(this.Text))
++++++++++++++++this.Text+=+Text_;
++++++++}
++++}
}
>++++xmlns:local="clr-namespace:app_name"
>++<local:CustomTextBox
>+++++++++++++++++x:Name="id_number_txt"
>+++++++++++++++++Width="240px"
>+++++++++++++++++Height="auto"/>|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|503648|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;

namespace App_name
{
 public class CustomTextBox : TextBox
 {
 private string Text_ = "";
 public CustomTextBox() : base()
 {}

 public string setHint
 {
 get { return Text_; }
 set { Text_ = value; }
 }
 protected override void OnGotFocus(RoutedEventArgs e)
 {
 base.OnGotFocus(e);
 if (Text_.Equals(this.Text))
 this.Clear();
 }
 protected override void OnLostFocus(RoutedEventArgs e)
 {
 base.OnLostFocus(e);
 if (String.IsNullOrWhiteSpace(this.Text))
 this.Text = Text_;
 }
 }
}
&gt; xmlns:local="clr-namespace:app_name"
&gt; &lt;local:CustomTextBox
&gt; x:Name="id_number_txt"
&gt; Width="240px"
&gt; Height="auto"/&gt;
</code></pre>

blocks|key|503675|text|你也可以尝试这样做..|type|unstyled|depth|inlineStyleRanges|entityRanges|data|503676|调用函数|503677|TextboxPlaceHolder(this.textBox1,+"YourPlaceHolder");|code-block|syntax|javascript|503678|编写此函数|503679|private+void+TextboxPlaceHolder(Control+control,+string+PlaceHolderText)
{
++++++++control.Text+=+PlaceHolderText;
++++++++control.GotFocus+%2B=+delegate+(object+sender,+EventArgs+args)
++++++++{
++++++++++++if+(cusmode+==+false)
++++++++++++{
++++++++++++++++control.Text+=+control.Text+==+PlaceHolderText+?+string.Empty+:+control.Text;
++++++++++++++++//IF+Focus+TextBox+forecolor+Black
++++++++++++++++control.ForeColor+=+Color.Black;
++++++++++++}
++++++++};

++++++++control.LostFocus+%2B=+delegate+(object+sender,+EventArgs+args)
++++++++{
++++++++++++if+(string.IsNullOrWhiteSpace(control.Text)+==+true)
++++++++++++{
++++++++++++++++control.Text+=+PlaceHolderText;
++++++++++++++++//If+not+focus+TextBox+forecolor+to+gray
++++++++++++++++control.ForeColor+=+Color.Gray;
++++++++++++}

++++++++};
}|503680|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You could also try in this way..

call the function

<pre><code>TextboxPlaceHolder(this.textBox1, "YourPlaceHolder");
</code></pre>

write this function

<pre><code>private void TextboxPlaceHolder(Control control, string PlaceHolderText)
{
 control.Text = PlaceHolderText;
 control.GotFocus += delegate (object sender, EventArgs args)
 {
 if (cusmode == false)
 {
 control.Text = control.Text == PlaceHolderText ? string.Empty : control.Text;
 //IF Focus TextBox forecolor Black
 control.ForeColor = Color.Black;
 }
 };

 control.LostFocus += delegate (object sender, EventArgs args)
 {
 if (string.IsNullOrWhiteSpace(control.Text) == true)
 {
 control.Text = PlaceHolderText;
 //If not focus TextBox forecolor to gray
 control.ForeColor = Color.Gray;
 }

 };
}
</code></pre>

blocks|key|503716|text|这里我带来了这个受@Kemal+Karadag启发的解决方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|503717|我注意到这里发布的每个解决方案都依赖于焦点，|503718|虽然我希望我的占位符是Google+Chrome中标准HTML占位符的精确克隆。|503719|不是在框被聚焦时隐藏/显示占位符，|503720|我根据框的文本长度隐藏/显示占位符：|503721|如果框为空，则显示占位符；如果在框中键入，则占位符消失。|503722|因为它是从标准TextBox继承的，所以你可以在你的工具箱中找到它！|503723|using+System;
using+System.Drawing;
using+System.Windows.Forms;

public+class+PlaceHolderTextBox+:+TextBox
{
++++private+bool+isPlaceHolder+=+true;
++++private+string+placeHolderText;

++++public+string+PlaceHolderText
++++{
++++++++get+{+return+placeHolderText;+}
++++++++set
++++++++{
++++++++++++placeHolderText+=+value;
++++++++++++SetPlaceholder();
++++++++}
++++}

++++public+PlaceHolderTextBox()
++++{
++++++++TextChanged+%2B=+OnTextChanged;
++++}

++++private+void+SetPlaceholder()
++++{
++++++++if+(!isPlaceHolder)
++++++++{
++++++++++++this.Text+=+placeHolderText;
++++++++++++this.ForeColor+=+Color.Gray;
++++++++++++isPlaceHolder+=+true;
++++++++}
++++}

++++private+void+RemovePlaceHolder()
++++{
++++++++if+(isPlaceHolder)
++++++++{
++++++++++++this.Text+=+this.Text[0].ToString();+//+Remove+placeHolder+text,+but+keep+the+character+we+just+entered
++++++++++++this.Select(1,+0);+//+Place+the+caret+after+the+character+we+just+entered
++++++++++++this.ForeColor+=+System.Drawing.SystemColors.WindowText;
++++++++++++isPlaceHolder+=+false;
++++++++}
++++}

++++private+void+OnTextChanged(object+sender,+EventArgs+e)
++++{
++++++++if+(this.Text.Length+==+0)
++++++++{
++++++++++++SetPlaceholder();
++++++++}
++++++++else
++++++++{
++++++++++++RemovePlaceHolder();
++++++++}
++++}
}|code-block|syntax|javascript|503724|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|Z|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|10|8|@]|9|@]|A|$]]|$1|N|3|O|5|P|7|11|8|@]|9|@]|A|$Q|R]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

Here I come with this solution inspired by @Kemal Karadag.

I noticed that every solution posted here is relying on the focus,

While I wanted my placeholder to be the exact clone of a standard HTML placeholder in Google Chrome.

Instead of hiding/showing the placeholder when the box is focused,

I hide/show the placeholder depending on the text length of the box:

If the box is empty, the placeholder is shown, and if you type in the box, the placeholder disappears.

As it is inherited from a standard TextBox, you can find it in your Toolbox!

<pre><code>using System;
using System.Drawing;
using System.Windows.Forms;

public class PlaceHolderTextBox : TextBox
{
 private bool isPlaceHolder = true;
 private string placeHolderText;

 public string PlaceHolderText
 {
 get { return placeHolderText; }
 set
 {
 placeHolderText = value;
 SetPlaceholder();
 }
 }

 public PlaceHolderTextBox()
 {
 TextChanged += OnTextChanged;
 }

 private void SetPlaceholder()
 {
 if (!isPlaceHolder)
 {
 this.Text = placeHolderText;
 this.ForeColor = Color.Gray;
 isPlaceHolder = true;
 }
 }

 private void RemovePlaceHolder()
 {
 if (isPlaceHolder)
 {
 this.Text = this.Text[0].ToString(); // Remove placeHolder text, but keep the character we just entered
 this.Select(1, 0); // Place the caret after the character we just entered
 this.ForeColor = System.Drawing.SystemColors.WindowText;
 isPlaceHolder = false;
 }
 }

 private void OnTextChanged(object sender, EventArgs e)
 {
 if (this.Text.Length == 0)
 {
 SetPlaceholder();
 }
 else
 {
 RemovePlaceHolder();
 }
 }
}
</code></pre>

blocks|key|287048|text|有更好的解决方案，但最简单的解决方案是:将textbox文本设置为所需的字符串，然后创建一个删除文本的函数，让该函数在textbox+Focus+Enter事件上触发|type|unstyled|depth|inlineStyleRanges|entityRanges|data|287049|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

there are BETTER solutions, but the easiest solution is here:
set the textbox text to your desired string
then create a function that deletes the text, have that function fire on textbox Focus Enter event

blocks|key|287076|text|用于WindowsForms+TextBox控件的非常有效的解决方案here。(对XAML不太确定)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|287077|这也将在多线模式下工作。|287078|它可能会扩展到其他控件，如ComboBox控件(未选中)|287079|entityMap|0|LINK|mutability|MUTABLE|url|https://mking.net/blog/cue-banners-in-winforms^0|Y|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]]]

Very effective solution <a href="https://mking.net/blog/cue-banners-in-winforms" rel="nofollow noreferrer">here</a> for WindowsForms TextBox control. (not sure about XAML).

This will work in Multliline mode also.

Probably it may be extended for other controls, like ComboBox control (not checked)

blocks|key|503826|text|我写了一个可重用的自定义控件，也许它可以帮助需要在他的项目中实现多个占位符文本框的人。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|503827|下面是一个实例的自定义类和实现示例，您可以通过使用VS将此代码粘贴到新的winforms项目中来轻松测试：|503828|namespace+reusebleplaceholdertextbox
{
++++public+partial+class+Form1+:+Form
++++{
++++++++public+Form1()
++++++++{
++++++++++++InitializeComponent();
++++++++}

++++++++private+void+Form1_Load(object+sender,+EventArgs+e)
++++++++{
++++++++++++//+implementation
++++++++++++CustomPlaceHolderTextbox+myCustomTxt+=+new+CustomPlaceHolderTextbox(
++++++++++++++++"Please+Write+Text+Here...",+Color.Gray,+new+Font("ARIAL",+11,+FontStyle.Italic)
++++++++++++++++,+Color.Black,+new+Font("ARIAL",+11,+FontStyle.Regular)
++++++++++++++++);

++++++++++++myCustomTxt.Multiline+=+true;
++++++++++++myCustomTxt.Size+=+new+Size(200,+50);
++++++++++++myCustomTxt.Location+=+new+Point(10,+10);
++++++++++++this.Controls.Add(myCustomTxt);
++++++++}
++++}

++++class+CustomPlaceHolderTextbox+:+System.Windows.Forms.TextBox
++++{
++++++++public+string+PlaceholderText+{+get;+private+set;+}
++++++++public+Color+PlaceholderForeColor+{+get;+private+set;+}
++++++++public+Font+PlaceholderFont+{+get;+private+set;+}

++++++++public+Color+TextForeColor+{+get;+private+set;+}
++++++++public+Font+TextFont+{+get;+private+set;+}

++++++++public+CustomPlaceHolderTextbox(string+placeholdertext,+Color+placeholderforecolor,
++++++++++++Font+placeholderfont,+Color+textforecolor,+Font+textfont)
++++++++{
++++++++++++this.PlaceholderText+=+placeholdertext;
++++++++++++this.PlaceholderFont+=+placeholderfont;
++++++++++++this.PlaceholderForeColor+=+placeholderforecolor;
++++++++++++this.PlaceholderFont+=+placeholderfont;
++++++++++++this.TextForeColor+=+textforecolor;
++++++++++++this.TextFont+=+textfont;
++++++++++++if+(!string.IsNullOrEmpty(this.PlaceholderText))
++++++++++++{
++++++++++++++++SetPlaceHolder(true);
++++++++++++++++this.Update();
++++++++++++}
++++++++}

++++++++private+void+SetPlaceHolder(bool+addEvents)
++++++++{
++++++++++++if+(addEvents)
++++++++++++{++
++++++++++++++++this.LostFocus+%2B=+txt_lostfocus;
++++++++++++++++this.Click+%2B=+txt_click;
++++++++++++}

++++++++++++this.Text+=+PlaceholderText;
++++++++++++this.ForeColor+=+PlaceholderForeColor;
++++++++++++this.Font+=+PlaceholderFont;
++++++++}

++++++++private+void+txt_click(object+sender,+EventArgs+e)
++++++++{
++++++++++++//+IsNotFirstClickOnThis:
++++++++++++//+if+there+is+no+other+control+in+the+form
++++++++++++//+we+will+have+a+problem+after+the+first+load
++++++++++++//+because+we+dont+other+focusable+control+to+move+the+focus+to
++++++++++++//+and+we+dont+want+to+remove+the+place+holder
++++++++++++//+only+on+first+time+the+place+holder+will+be+removed+by+click+event
++++++++++++RemovePlaceHolder();
++++++++++++this.GotFocus+%2B=+txt_focus;
++++++++++++//+no+need+for+this+event+listener+now
++++++++++++this.Click+-=+txt_click;
++++++++}

++++++++private+void+RemovePlaceHolder()
++++++++{
++++++++++++this.Text+=+"";
++++++++++++this.ForeColor+=+TextForeColor;
++++++++++++this.Font+=+TextFont;
++++++++}
++++++++private+void+txt_lostfocus(object+sender,+EventArgs+e)
++++++++{
++++++++++++if+(string.IsNullOrEmpty(this.Text))
++++++++++++{
++++++++++++++++//+set+placeholder+again
++++++++++++++++SetPlaceHolder(false);
++++++++++++}
++++++++}

++++++++private+void+txt_focus(object+sender,+EventArgs+e)
++++++++{
++++++++++++if+(this.Text+==+PlaceholderText)
++++++++++++{
++++++++++++++++//+IsNotFirstClickOnThis:
++++++++++++++++//+if+there+is+no+other+control+in+the+form
++++++++++++++++//+we+will+have+a+problem+after+the+first+load
++++++++++++++++//+because+we+dont+other+focusable+control+to+move+the+focus+to
++++++++++++++++//+and+we+dont+want+to+remove+the+place+holder
++++++++++++++++RemovePlaceHolder();
++++++++++++}
++++++++}
++++}
}|code-block|syntax|javascript|503829|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I wrote a reusable custom control, maybe it can help someone that need to implement multiple placeholder textboxes in his project. here is the custom class with implementation example of an instance, you can test easily by pasting this code on a new winforms project using VS:

<pre><code>namespace reusebleplaceholdertextbox
{
 public partial class Form1 : Form
 {
 public Form1()
 {
 InitializeComponent();
 }

 private void Form1_Load(object sender, EventArgs e)
 {
 // implementation
 CustomPlaceHolderTextbox myCustomTxt = new CustomPlaceHolderTextbox(
 "Please Write Text Here...", Color.Gray, new Font("ARIAL", 11, FontStyle.Italic)
 , Color.Black, new Font("ARIAL", 11, FontStyle.Regular)
 );

 myCustomTxt.Multiline = true;
 myCustomTxt.Size = new Size(200, 50);
 myCustomTxt.Location = new Point(10, 10);
 this.Controls.Add(myCustomTxt);
 }
 }

 class CustomPlaceHolderTextbox : System.Windows.Forms.TextBox
 {
 public string PlaceholderText { get; private set; }
 public Color PlaceholderForeColor { get; private set; }
 public Font PlaceholderFont { get; private set; }

 public Color TextForeColor { get; private set; }
 public Font TextFont { get; private set; }

 public CustomPlaceHolderTextbox(string placeholdertext, Color placeholderforecolor,
 Font placeholderfont, Color textforecolor, Font textfont)
 {
 this.PlaceholderText = placeholdertext;
 this.PlaceholderFont = placeholderfont;
 this.PlaceholderForeColor = placeholderforecolor;
 this.PlaceholderFont = placeholderfont;
 this.TextForeColor = textforecolor;
 this.TextFont = textfont;
 if (!string.IsNullOrEmpty(this.PlaceholderText))
 {
 SetPlaceHolder(true);
 this.Update();
 }
 }

 private void SetPlaceHolder(bool addEvents)
 {
 if (addEvents)
 { 
 this.LostFocus += txt_lostfocus;
 this.Click += txt_click;
 }

 this.Text = PlaceholderText;
 this.ForeColor = PlaceholderForeColor;
 this.Font = PlaceholderFont;
 }

 private void txt_click(object sender, EventArgs e)
 {
 // IsNotFirstClickOnThis:
 // if there is no other control in the form
 // we will have a problem after the first load
 // because we dont other focusable control to move the focus to
 // and we dont want to remove the place holder
 // only on first time the place holder will be removed by click event
 RemovePlaceHolder();
 this.GotFocus += txt_focus;
 // no need for this event listener now
 this.Click -= txt_click;
 }

 private void RemovePlaceHolder()
 {
 this.Text = "";
 this.ForeColor = TextForeColor;
 this.Font = TextFont;
 }
 private void txt_lostfocus(object sender, EventArgs e)
 {
 if (string.IsNullOrEmpty(this.Text))
 {
 // set placeholder again
 SetPlaceHolder(false);
 }
 }

 private void txt_focus(object sender, EventArgs e)
 {
 if (this.Text == PlaceholderText)
 {
 // IsNotFirstClickOnThis:
 // if there is no other control in the form
 // we will have a problem after the first load
 // because we dont other focusable control to move the focus to
 // and we dont want to remove the place holder
 RemovePlaceHolder();
 }
 }
 }
}
</code></pre>

blocks|key|287150|text|就像一种护身符。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|287151|public+class+WTextBox+:+TextBox
{
++++private+string+_placeholder;


++++[Category("Appearance")]
++++public+string+Placeholder
++++{
++++++++get+{+return+_placeholder;+}
++++++++set
++++++++{
++++++++++++_placeholder+=+value+??+string.Empty;
++++++++++++Invalidate();
++++++++}
++++}

++++public+WTextBox()
++++{
++++++++_placeholder+=+string.Empty;
++++}

++++protected+override+void+WndProc(ref+Message+m)
++++{
++++++++base.WndProc(ref+m);

++++++++if+(m.Msg+!=+0xF+%7C%7C+Focused+%7C%7C+!string.IsNullOrEmpty(Text)+%7C%7C+string.IsNullOrWhiteSpace(_placeholder))
++++++++{
++++++++++++return;
++++++++}

++++++++using+(var+g+=+CreateGraphics())
++++++++{
++++++++++++TextRenderer.DrawText(g,+_placeholder,+Font,+ClientRectangle,+SystemColors.GrayText,+BackColor,+TextFormatFlags.Left);
++++++++}
++++}
}|code-block|syntax|javascript|287152|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Works like a charm.

<pre><code>public class WTextBox : TextBox
{
 private string _placeholder;


 [Category("Appearance")]
 public string Placeholder
 {
 get { return _placeholder; }
 set
 {
 _placeholder = value ?? string.Empty;
 Invalidate();
 }
 }

 public WTextBox()
 {
 _placeholder = string.Empty;
 }

 protected override void WndProc(ref Message m)
 {
 base.WndProc(ref m);

 if (m.Msg != 0xF || Focused || !string.IsNullOrEmpty(Text) || string.IsNullOrWhiteSpace(_placeholder))
 {
 return;
 }

 using (var g = CreateGraphics())
 {
 TextRenderer.DrawText(g, _placeholder, Font, ClientRectangle, SystemColors.GrayText, BackColor, TextFormatFlags.Left);
 }
 }
}
</code></pre>

blocks|key|503887|text|这是texbox的一个扩展方法。只需以编程方式添加占位符文本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|503888|myTextBox.AddPlaceholderText("Hello+World!");|code-block|syntax|javascript|503889|扩展方法：|503890|public+static+void+AddPlaceholderText(this+TextBox+textBox,+string+placeholderText)
++++++++{
++++++++++++if+(string.IsNullOrWhiteSpace(textBox.Text))
++++++++++++++++textBox.Text+=+placeholderText;
++++++++++++textBox.SetResourceReference(Control.ForegroundProperty,
++++++++++++++++textBox.Text+!=+placeholderText
++++++++++++++++++++?+"SystemControlForegroundBaseHighBrush"
++++++++++++++++++++:+"SystemControlForegroundBaseMediumBrush");
++++++++++++var+ignoreSelectionChanged+=+false;
++++++++++++textBox.SelectionChanged+%2B=+(sender,+args)+=>
++++++++++++{
++++++++++++++++if+(ignoreSelectionChanged)+{+ignoreSelectionChanged+=+false;+return;+}
++++++++++++++++if+(textBox.Text+!=+placeholderText)+return;
++++++++++++++++ignoreSelectionChanged+=+true;
++++++++++++++++textBox.Select(0,+0);
++++++++++++};
++++++++++++var+lastText+=+textBox.Text;
++++++++++++var+ignoreTextChanged+=+false;
++++++++++++textBox.TextChanged+%2B=+(sender,+args)+=>
++++++++++++{
++++++++++++++++if+(ignoreTextChanged)+{+ignoreTextChanged+=+false;+return;+}
++++++++++++++++if+(string.IsNullOrWhiteSpace(textBox.Text))
++++++++++++++++{
++++++++++++++++++++ignoreTextChanged+=+true;
++++++++++++++++++++textBox.Text+=+placeholderText;
++++++++++++++++++++textBox.Select(0,+0);
++++++++++++++++}
++++++++++++++++else+if+(lastText+==+placeholderText)
++++++++++++++++{
++++++++++++++++++++ignoreTextChanged+=+true;
++++++++++++++++++++textBox.Text+=+textBox.Text.Substring(0,+1);
++++++++++++++++++++textBox.Select(1,+0);
++++++++++++++++}

++++++++++++++++textBox.SetResourceReference(Control.ForegroundProperty,
++++++++++++++++++++textBox.Text+!=+placeholderText
++++++++++++++++++++++++?+"SystemControlForegroundBaseHighBrush"
++++++++++++++++++++++++:+"SystemControlForegroundBaseMediumBrush");
++++++++++++++++lastText+=+textBox.Text;
++++++++++++};
++++++++}|503891|快乐的编码，BierDav|503892|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

This is a extension method for the texbox. Simply Add the Placeholder Text programmatically:
<pre><code>myTextBox.AddPlaceholderText(&quot;Hello World!&quot;);
</code></pre>
The extension method:
<pre><code>public static void AddPlaceholderText(this TextBox textBox, string placeholderText)
 {
 if (string.IsNullOrWhiteSpace(textBox.Text))
 textBox.Text = placeholderText;
 textBox.SetResourceReference(Control.ForegroundProperty,
 textBox.Text != placeholderText
 ? &quot;SystemControlForegroundBaseHighBrush&quot;
 : &quot;SystemControlForegroundBaseMediumBrush&quot;);
 var ignoreSelectionChanged = false;
 textBox.SelectionChanged += (sender, args) =&gt;
 {
 if (ignoreSelectionChanged) { ignoreSelectionChanged = false; return; }
 if (textBox.Text != placeholderText) return;
 ignoreSelectionChanged = true;
 textBox.Select(0, 0);
 };
 var lastText = textBox.Text;
 var ignoreTextChanged = false;
 textBox.TextChanged += (sender, args) =&gt;
 {
 if (ignoreTextChanged) { ignoreTextChanged = false; return; }
 if (string.IsNullOrWhiteSpace(textBox.Text))
 {
 ignoreTextChanged = true;
 textBox.Text = placeholderText;
 textBox.Select(0, 0);
 }
 else if (lastText == placeholderText)
 {
 ignoreTextChanged = true;
 textBox.Text = textBox.Text.Substring(0, 1);
 textBox.Select(1, 0);
 }

 textBox.SetResourceReference(Control.ForegroundProperty,
 textBox.Text != placeholderText
 ? &quot;SystemControlForegroundBaseHighBrush&quot;
 : &quot;SystemControlForegroundBaseMediumBrush&quot;);
 lastText = textBox.Text;
 };
 }
</code></pre>
Happy coding, BierDav

blocks|key|503967|text|让我们用PlcaeHoldText和PlaceHoldBackround扩展TextBox。我从我的项目中剥离了一些代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|503968|与Grid或Canvas说再见！|503969|<TextBox+x:Class="VcpkgGui.View.PlaceHoldedTextBox"
+++++++++++++xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+++++++++++++xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+++++++++++++xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"+
+++++++++++++xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+++++++++++++xmlns:local="clr-namespace:VcpkgGui.View"
+++++++++++++mc:Ignorable="d"
+++++++++++++Name="placeHoldTextBox"
+++++++++++++TextAlignment="Left"
+++++++++>
++++<TextBox.Resources>
++++++++<local:FrameworkWidthConverter+x:Key="getElemWidth"/>
++++++++<local:FrameworkHeightConverter+x:Key="getElemHeight"/>
++++++++<VisualBrush+x:Key="PlaceHoldTextBrush"+TileMode="None"+Stretch="None"+AlignmentX="Left"+AlignmentY="Center"+Opacity="1">
++++++++++++<VisualBrush.Visual>
++++++++++++++++<Border+Background="{Binding+ElementName=placeHoldTextBox,+Path=PlaceHoldBackground}"
++++++++++++++++++++++++BorderThickness="0"
++++++++++++++++++++++++Margin="0,0,0,0"
++++++++++++++++++++++++Width="{Binding+Mode=OneWay,+ElementName=placeHoldTextBox,+Converter={StaticResource+getElemWidth}}"
++++++++++++++++++++++++Height="{Binding+Mode=OneWay,+ElementName=placeHoldTextBox,+Converter={StaticResource+getElemHeight}}"
++++++++++++++++++++++++>
++++++++++++++++++++<Label+Content="{Binding+ElementName=placeHoldTextBox,+Path=PlaceHoldText}"
+++++++++++++++++++++++++++Background="Transparent"
+++++++++++++++++++++++++++Foreground="#88000000"
+++++++++++++++++++++++++++HorizontalAlignment="Stretch"
+++++++++++++++++++++++++++VerticalAlignment="Stretch"
+++++++++++++++++++++++++++HorizontalContentAlignment="Left"
+++++++++++++++++++++++++++VerticalContentAlignment="Center"
+++++++++++++++++++++++++++ClipToBounds="True"
+++++++++++++++++++++++++++Padding="0,0,0,0"
+++++++++++++++++++++++++++FontSize="14"
+++++++++++++++++++++++++++FontStyle="Normal"
+++++++++++++++++++++++++++Opacity="1"/>
++++++++++++++++</Border>
++++++++++++</VisualBrush.Visual>
++++++++</VisualBrush>
++++</TextBox.Resources>
++++<TextBox.Style>
++++++++<Style+TargetType="TextBox">
++++++++++++<Style.Triggers>
++++++++++++++++<Trigger+Property="Text"+Value="{x:Null}">
++++++++++++++++++++<Setter+Property="Background"++Value="{StaticResource+PlaceHoldTextBrush}"/>
++++++++++++++++</Trigger>
++++++++++++++++<Trigger+Property="Text"+Value="">
++++++++++++++++++++<Setter+Property="Background"++Value="{StaticResource+PlaceHoldTextBrush}"/>
++++++++++++++++</Trigger>
++++++++++++</Style.Triggers>
++++++++</Style>
++++</TextBox.Style>
</TextBox>|code-block|syntax|javascript|503970|using+System;
using+System.Collections.Generic;
using+System.Globalization;
using+System.Linq;
using+System.Text;
using+System.Threading.Tasks;
using+System.Windows;
using+System.Windows.Controls;
using+System.Windows.Data;
using+System.Windows.Documents;
using+System.Windows.Input;
using+System.Windows.Media;
using+System.Windows.Media.Imaging;
using+System.Windows.Navigation;
using+System.Windows.Shapes;

namespace+VcpkgGui.View
{
++++///+<summary>
++++///+PlaceHoldedTextBox.xaml+的交互逻辑
++++///+</summary>
++++public+partial+class+PlaceHoldedTextBox+:+TextBox
++++{

++++++++public+string+PlaceHoldText
++++++++{
++++++++++++get+{+return+(string)GetValue(PlaceHoldTextProperty);+}
++++++++++++set+{+SetValue(PlaceHoldTextProperty,+value);+}
++++++++}

++++++++//+Using+a+DependencyProperty+as+the+backing+store+for+PlaceHolderText.++This+enables+animation,+styling,+binding,+etc...
++++++++public+static+readonly+DependencyProperty+PlaceHoldTextProperty+=
++++++++++++DependencyProperty.Register("PlaceHoldText",+typeof(string),+typeof(PlaceHoldedTextBox),+new+PropertyMetadata(string.Empty));



++++++++public+Brush+PlaceHoldBackground
++++++++{
++++++++++++get+{+return+(Brush)GetValue(PlaceHoldBackgroundProperty);+}
++++++++++++set+{+SetValue(PlaceHoldBackgroundProperty,+value);+}
++++++++}

++++++++public+static+readonly+DependencyProperty+PlaceHoldBackgroundProperty+=
++++++++++++DependencyProperty.Register(nameof(PlaceHoldBackground),+typeof(Brush),+typeof(PlaceHoldedTextBox),+new+PropertyMetadata(Brushes.White));

++++++++public+PlaceHoldedTextBox()+:base()
++++++++{
++++++++++++InitializeComponent();
++++++++}
++++}

++++[ValueConversion(typeof(FrameworkElement),+typeof(double))]
++++internal+class+FrameworkWidthConverter+:+System.Windows.Data.IValueConverter
++++{
++++++++public+object+Convert(object+value,+Type+targetType,+object+parameter,+CultureInfo+culture)
++++++++{
++++++++++++if(value+is+FrameworkElement+elem)
++++++++++++++++return+double.IsNaN(elem.Width)+?+elem.ActualWidth+:+elem.Width;
++++++++++++else
++++++++++++++++return+DependencyProperty.UnsetValue;
++++++++}

++++++++public+object+ConvertBack(object+value,+Type+targetType,+object+parameter,+CultureInfo+culture)
++++++++{
++++++++++++return+DependencyProperty.UnsetValue;
++++++++}
++++}

++++[ValueConversion(typeof(FrameworkElement),+typeof(double))]
++++internal+class+FrameworkHeightConverter+:+System.Windows.Data.IValueConverter
++++{
++++++++public+object+Convert(object+value,+Type+targetType,+object+parameter,+CultureInfo+culture)
++++++++{
++++++++++++if+(value+is+FrameworkElement+elem)
++++++++++++++++return+double.IsNaN(elem.Height)+?+elem.ActualHeight+:+elem.Height;
++++++++++++else
++++++++++++++++return+DependencyProperty.UnsetValue;
++++++++}

++++++++public+object+ConvertBack(object+value,+Type+targetType,+object+parameter,+CultureInfo+culture)
++++++++{
++++++++++++return+DependencyProperty.UnsetValue;
++++++++}
++++}

}|503971|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|F|7|P|8|@]|9|@]|A|$G|H]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Let's extend the TextBox with PlcaeHoldText and PlaceHoldBackround. I stripped some code form my project.
say goodbye to Grid or Canvas!
<pre><code>&lt;TextBox x:Class=&quot;VcpkgGui.View.PlaceHoldedTextBox&quot;
 xmlns=&quot;http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
 xmlns:x=&quot;http://schemas.microsoft.com/winfx/2006/xaml&quot;
 xmlns:mc=&quot;http://schemas.openxmlformats.org/markup-compatibility/2006&quot; 
 xmlns:d=&quot;http://schemas.microsoft.com/expression/blend/2008&quot;
 xmlns:local=&quot;clr-namespace:VcpkgGui.View&quot;
 mc:Ignorable=&quot;d&quot;
 Name=&quot;placeHoldTextBox&quot;
 TextAlignment=&quot;Left&quot;
 &gt;
 &lt;TextBox.Resources&gt;
 &lt;local:FrameworkWidthConverter x:Key=&quot;getElemWidth&quot;/&gt;
 &lt;local:FrameworkHeightConverter x:Key=&quot;getElemHeight&quot;/&gt;
 &lt;VisualBrush x:Key=&quot;PlaceHoldTextBrush&quot; TileMode=&quot;None&quot; Stretch=&quot;None&quot; AlignmentX=&quot;Left&quot; AlignmentY=&quot;Center&quot; Opacity=&quot;1&quot;&gt;
 &lt;VisualBrush.Visual&gt;
 &lt;Border Background=&quot;{Binding ElementName=placeHoldTextBox, Path=PlaceHoldBackground}&quot;
 BorderThickness=&quot;0&quot;
 Margin=&quot;0,0,0,0&quot;
 Width=&quot;{Binding Mode=OneWay, ElementName=placeHoldTextBox, Converter={StaticResource getElemWidth}}&quot;
 Height=&quot;{Binding Mode=OneWay, ElementName=placeHoldTextBox, Converter={StaticResource getElemHeight}}&quot;
 &gt;
 &lt;Label Content=&quot;{Binding ElementName=placeHoldTextBox, Path=PlaceHoldText}&quot;
 Background=&quot;Transparent&quot;
 Foreground=&quot;#88000000&quot;
 HorizontalAlignment=&quot;Stretch&quot;
 VerticalAlignment=&quot;Stretch&quot;
 HorizontalContentAlignment=&quot;Left&quot;
 VerticalContentAlignment=&quot;Center&quot;
 ClipToBounds=&quot;True&quot;
 Padding=&quot;0,0,0,0&quot;
 FontSize=&quot;14&quot;
 FontStyle=&quot;Normal&quot;
 Opacity=&quot;1&quot;/&gt;
 &lt;/Border&gt;
 &lt;/VisualBrush.Visual&gt;
 &lt;/VisualBrush&gt;
 &lt;/TextBox.Resources&gt;
 &lt;TextBox.Style&gt;
 &lt;Style TargetType=&quot;TextBox&quot;&gt;
 &lt;Style.Triggers&gt;
 &lt;Trigger Property=&quot;Text&quot; Value=&quot;{x:Null}&quot;&gt;
 &lt;Setter Property=&quot;Background&quot; Value=&quot;{StaticResource PlaceHoldTextBrush}&quot;/&gt;
 &lt;/Trigger&gt;
 &lt;Trigger Property=&quot;Text&quot; Value=&quot;&quot;&gt;
 &lt;Setter Property=&quot;Background&quot; Value=&quot;{StaticResource PlaceHoldTextBrush}&quot;/&gt;
 &lt;/Trigger&gt;
 &lt;/Style.Triggers&gt;
 &lt;/Style&gt;
 &lt;/TextBox.Style&gt;
&lt;/TextBox&gt;
</code></pre>
<pre><code>using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace VcpkgGui.View
{
 /// &lt;summary&gt;
 /// PlaceHoldedTextBox.xaml 的交互逻辑
 /// &lt;/summary&gt;
 public partial class PlaceHoldedTextBox : TextBox
 {

 public string PlaceHoldText
 {
 get { return (string)GetValue(PlaceHoldTextProperty); }
 set { SetValue(PlaceHoldTextProperty, value); }
 }

 // Using a DependencyProperty as the backing store for PlaceHolderText. This enables animation, styling, binding, etc...
 public static readonly DependencyProperty PlaceHoldTextProperty =
 DependencyProperty.Register(&quot;PlaceHoldText&quot;, typeof(string), typeof(PlaceHoldedTextBox), new PropertyMetadata(string.Empty));



 public Brush PlaceHoldBackground
 {
 get { return (Brush)GetValue(PlaceHoldBackgroundProperty); }
 set { SetValue(PlaceHoldBackgroundProperty, value); }
 }

 public static readonly DependencyProperty PlaceHoldBackgroundProperty =
 DependencyProperty.Register(nameof(PlaceHoldBackground), typeof(Brush), typeof(PlaceHoldedTextBox), new PropertyMetadata(Brushes.White));

 public PlaceHoldedTextBox() :base()
 {
 InitializeComponent();
 }
 }

 [ValueConversion(typeof(FrameworkElement), typeof(double))]
 internal class FrameworkWidthConverter : System.Windows.Data.IValueConverter
 {
 public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
 {
 if(value is FrameworkElement elem)
 return double.IsNaN(elem.Width) ? elem.ActualWidth : elem.Width;
 else
 return DependencyProperty.UnsetValue;
 }

 public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
 {
 return DependencyProperty.UnsetValue;
 }
 }

 [ValueConversion(typeof(FrameworkElement), typeof(double))]
 internal class FrameworkHeightConverter : System.Windows.Data.IValueConverter
 {
 public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
 {
 if (value is FrameworkElement elem)
 return double.IsNaN(elem.Height) ? elem.ActualHeight : elem.Height;
 else
 return DependencyProperty.UnsetValue;
 }

 public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
 {
 return DependencyProperty.UnsetValue;
 }
 }

}
</code></pre>

blocks|key|287267|text|我知道这是一个旧线程，但是.NET核心和.NET+5.0已经实现了TextBox.PlaceholderText属性。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|287268|https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.textbox.placeholdertext?view=net-5.0|287269|entityMap|0|LINK|mutability|MUTABLE|url^0|X|N|0|0|2T|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@$9|S|A|T|1|U]]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|G]]]]

I know this is an old thread, but .NET Core and .NET 5.0 have implemented the <code>TextBox.PlaceholderText</code> Property.
<a href="https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.textbox.placeholdertext?view=net-5.0" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.textbox.placeholdertext?view=net-5.0</a>

I am looking for a way to add placeholder text to a textbox like you can with a textbox in html5. 

I.e. if the textbox has no text, then it adds the text <code>Enter some text here</code>, when the user clicks on it the placeholder text disappears and allows the user to enter their own text, and if the textbox loses focus and there is still no text then the placeholder is added back to the textbox.

Adding placeholder text to textbox

Windows

我正在寻找一种方法来添加占位符文本到文本框中，就像你可以在html5中使用文本框。即，如果文本框没有文本，则它添加文本Enter some text here，当用户点击它时，占位符文本消失并且允许用户输入他们自己的文本，并且如果文本框失去焦点并且仍然没有文本，则该占位符被添加回文本框。

问向文本框添加占位符文本
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