blocks|key|1567165|text|向TextBox添加一个回调，该回调将在每个笔划上触发。在这样的回调中测试是否为空，并启用/禁用该按钮。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1567166|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|$]]

<p>Add a callback to the TextBox that fires on every stroke. Test for emptiness in such callback and enable/disable the button.</p>


blocks|key|1567239|text|使用简单命令|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1567240|<TextBox+Text={Binding+Path=TitleText}/>

<Button+Command="{Binding+Path=ClearTextCommand}"+Content="Clear+Text"/>|code-block|syntax|javascript|1567241|以下是View+Model中的示例代码|1567242|public+class+MyViewModel+:+INotifyPropertyChanged
{
++++public+ICommand+ClearTextCommand+{+get;+private+set;+}

++++private+string+_titleText;+
++++public+string+TitleText
++++{
++++++++get+{+return+_titleText;+}
++++++++set
++++++++{
++++++++++++if+(value+==+_titleText)
++++++++++++++++return;

++++++++++++_titleText+=+value;
++++++++++++this.OnPropertyChanged("TitleText");
++++++++}
++++}+++

++++public+MyViewModel()
++++{
++++++++ClearTextCommand+=+new+SimpleCommand
++++++++++++{
++++++++++++++++ExecuteDelegate+=+x+=>+TitleText="",
++++++++++++++++CanExecuteDelegate+=+x+=>+TitleText.Length+>+0
++++++++++++};++
++++}++++++++++++

++++public+event+PropertyChangedEventHandler+PropertyChanged;

++++protected+void+OnPropertyChanged(string+propertyName)
++++{
++++++++PropertyChangedEventHandler+handler+=+this.PropertyChanged;
++++++++if+(handler+!=+null)
++++++++++++handler(this,+new+PropertyChangedEventArgs(propertyName));
++++}+++++
}|1567243|有关更多信息，请参阅Marlon+Grechs+SimpleCommand|offset|length|1567244|也可以从http://blogs.msdn.com/llobo/archive/2009/05/01/download-m-v-vm-project-template-toolkit.aspx查看MVVM+Project+Template/Toolkit。它使用DelegateCommand进行命令，它应该是任何项目的一个很好的启动模板。|1567245|entityMap|0|LINK|mutability|MUTABLE|url|http://marlongrech.wordpress.com/2008/11/26/avoiding-commandbinding-in-the-xaml-code-behind-files/|1|http://blogs.msdn.com/llobo/archive/2009/05/01/download-m-v-vm-project-template-toolkit.aspx^0|0|0|0|0|O|D|0|0|4|2K|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|14|8|@]|9|@$M|15|N|16|1|17]]|A|$]]|$1|O|3|P|5|6|7|18|8|@]|9|@$M|19|N|1A|1|1B]]|A|$]]|$1|Q|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]|Y|$5|T|U|V|A|$W|Z]]]]

<p>Use the Simple Command</p>

<pre><code>&lt;TextBox Text={Binding Path=TitleText}/&gt;

&lt;Button Command="{Binding Path=ClearTextCommand}" Content="Clear Text"/&gt;
</code></pre>

<p>Here is the sample code in the View Model</p>

<pre><code>public class MyViewModel : INotifyPropertyChanged
{
    public ICommand ClearTextCommand { get; private set; }

    private string _titleText; 
    public string TitleText
    {
        get { return _titleText; }
        set
        {
            if (value == _titleText)
                return;

            _titleText = value;
            this.OnPropertyChanged("TitleText");
        }
    }   

    public MyViewModel()
    {
        ClearTextCommand = new SimpleCommand
            {
                ExecuteDelegate = x =&gt; TitleText="",
                CanExecuteDelegate = x =&gt; TitleText.Length &gt; 0
            };  
    }            

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs(propertyName));
    }     
}
</code></pre>

<p>For more information see Marlon Grechs <a href="http://marlongrech.wordpress.com/2008/11/26/avoiding-commandbinding-in-the-xaml-code-behind-files/" rel="nofollow noreferrer">SimpleCommand</a></p>

<p>Also check out the MVVM Project Template/Toolkit from <a href="http://blogs.msdn.com/llobo/archive/2009/05/01/download-m-v-vm-project-template-toolkit.aspx" rel="nofollow noreferrer">http://blogs.msdn.com/llobo/archive/2009/05/01/download-m-v-vm-project-template-toolkit.aspx</a>. It uses the DelegateCommand for commanding and it should be a great starting template for any project.</p>


blocks|key|1351812|text|如果您没有使用命令，另一种方法是使用Converter。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1351813|例如，使用一般的Int+to+Bool转换器：|1351814|++[ValueConversion(typeof(int),+typeof(bool))]
++public+class+IntToBoolConverter+:+IValueConverter
++{
++++#region+IValueConverter+Members

++++public+object+Convert(object+value,+Type+targetType,+object+parameter,+CultureInfo+culture)
++++{
++++++try
++++++{
++++++++return+(System.Convert.ToInt32(value)+>+0);
++++++}
++++++catch+(InvalidCastException)
++++++{
++++++++return+DependencyProperty.UnsetValue;
++++++}
++++}

++++public+object+ConvertBack(object+value,+Type+targetType,+object+parameter,+CultureInfo+culture)
++++{
++++++return+System.Convert.ToBoolean(value)+?+1+:+0;
++++}

++++#endregion
++}|code-block|syntax|javascript|1351815|然后在buttons的IsEnabled属性上：|1351816|<Button+IsEnabled={Binding+ElementName=TextBoxName,+Path=Text.Length,+Converter={StaticResource+IntToBoolConverter}}/>|1351817|HTH，|1351818|丹尼斯|1351819|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

<p>IF you were not using Commands, another alternative is using a Converter.</p>

<p>For example, using a generic Int to Bool converter:</p>

<pre><code>  [ValueConversion(typeof(int), typeof(bool))]
  public class IntToBoolConverter : IValueConverter
  {
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
      try
      {
        return (System.Convert.ToInt32(value) &gt; 0);
      }
      catch (InvalidCastException)
      {
        return DependencyProperty.UnsetValue;
      }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
      return System.Convert.ToBoolean(value) ? 1 : 0;
    }

    #endregion
  }
</code></pre>

<p>Then on the buttons IsEnabled property: </p>

<pre><code>&lt;Button IsEnabled={Binding ElementName=TextBoxName, Path=Text.Length, Converter={StaticResource IntToBoolConverter}}/&gt;
</code></pre>

<p>HTH, </p>

<p>Dennis</p>


blocks|key|1567325|text|使用触发器！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1567326|<TextBox+x:Name="txt_Titel+/>
<Button+Content="Transfer"+d:IsLocked="True">
++<Button.Style>
++++<Style>
++++++<Style.Triggers>
++++++++<DataTrigger+Binding="{Binding+ElementName=txt_Titel,+Path=Text}"+Value="">
+++++++++<Setter+Property="Button.IsEnabled"+Value="false"/>
++++++++</DataTrigger>
++++++</Style.Triggers>
++++</Style>
++</Button.Style>
</Button>|code-block|syntax|javascript|1567327|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|$]]

<p>Use a trigger!</p>

<pre><code>&lt;TextBox x:Name="txt_Titel /&gt;
&lt;Button Content="Transfer" d:IsLocked="True"&gt;
  &lt;Button.Style&gt;
    &lt;Style&gt;
      &lt;Style.Triggers&gt;
        &lt;DataTrigger Binding="{Binding ElementName=txt_Titel, Path=Text}" Value=""&gt;
         &lt;Setter Property="Button.IsEnabled" Value="false"/&gt;
        &lt;/DataTrigger&gt;
      &lt;/Style.Triggers&gt;
    &lt;/Style&gt;
  &lt;/Button.Style&gt;
&lt;/Button&gt;
</code></pre>


blocks|key|1351913|text|为什么每个人都把事情搞得这么复杂！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1351914|++++<TextBox+x:Name="TB"/>
++++<Button+IsEnabled="{Binding+ElementName=TB,Path=Text.Length}">Test</Button>|code-block|syntax|javascript|1351915|不需要别的了......|1351916|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|$]]

<p>Why is everyone making things so complicated!</p>

<pre><code>    &lt;TextBox x:Name="TB"/&gt;
    &lt;Button IsEnabled="{Binding ElementName=TB,Path=Text.Length}"&gt;Test&lt;/Button&gt;
</code></pre>

<p>Nothing else needed......</p>


blocks|key|1567430|text|这方面的关键在于绑定本身。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1567431|添加UpdateSourceTrigger+=+PropertyChanged|1567432|这是最简单的解决方案|1567433|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

<p>The key on this is on the binding itself..</p>

<p>
</p>

<p>Add UpdateSourceTrigger = PropertyChanged</p>

<p>this is the most simple solution</p>


<p>What is the simplest way in WPF to enable a <code>Button</code> when the user types something into a <code>TextBox</code>?</p>


How to enable a button when a user types into a textbox

在WPF中，当用户在TextBox中键入内容时启用Button的最简单方法是什么

问如何在用户向文本框中键入内容时启用按钮
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