blocks|key|717488|text|您可以使用以下代码片段：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|717489|private+void+textBox1_TextChanged(object+sender,+EventArgs+e)
{
++++if+(!System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text,+"%5E[a-zA-Z+]"))
++++{
++++++++MessageBox.Show("This+textbox+accepts+only+alphabetical+characters");
++++++++textBox1.Text.Remove(textBox1.Text.Length+-+1);
++++}
}|code-block|syntax|javascript|717490|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 could use the following snippet:

<pre><code>private void textBox1_TextChanged(object sender, EventArgs e)
{
 if (!System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, "^[a-zA-Z ]"))
 {
 MessageBox.Show("This textbox accepts only alphabetical characters");
 textBox1.Text.Remove(textBox1.Text.Length - 1);
 }
}
</code></pre>

blocks|key|501564|text|最简单的方法是处理TextChangedEvent并检查输入的内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|501565|string+oldText+=+string.Empty;
++++private+void+textBox2_TextChanged(object+sender,+EventArgs+e)
++++{
++++++++if+(textBox2.Text.All(chr+=>+char.IsLetter(chr)))
++++++++{
++++++++++++oldText+=+textBox2.Text;
++++++++++++textBox2.Text+=+oldText;

++++++++++++textBox2.BackColor+=+System.Drawing.Color.White;
++++++++++++textBox2.ForeColor+=+System.Drawing.Color.Black;
++++++++}
++++++++else
++++++++{
++++++++++++textBox2.Text+=+oldText;
++++++++++++textBox2.BackColor+=+System.Drawing.Color.Red;
++++++++++++textBox2.ForeColor+=+System.Drawing.Color.White;
++++++++}
++++++++textBox2.SelectionStart+=+textBox2.Text.Length;
++++}|code-block|syntax|javascript|501566|如果你愿意，这是一个无正则表达式的版本。它会使文本框在输入错误时闪烁。请注意，它似乎也支持粘贴操作。|501567|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|$]]

The simplest way is to handle the TextChangedEvent and check what's been typed:

<pre><code>string oldText = string.Empty;
 private void textBox2_TextChanged(object sender, EventArgs e)
 {
 if (textBox2.Text.All(chr =&gt; char.IsLetter(chr)))
 {
 oldText = textBox2.Text;
 textBox2.Text = oldText;

 textBox2.BackColor = System.Drawing.Color.White;
 textBox2.ForeColor = System.Drawing.Color.Black;
 }
 else
 {
 textBox2.Text = oldText;
 textBox2.BackColor = System.Drawing.Color.Red;
 textBox2.ForeColor = System.Drawing.Color.White;
 }
 textBox2.SelectionStart = textBox2.Text.Length;
 }
</code></pre>

This is a regex-free version if you prefer. It will make the text box blink on bad input.
Please note that it also seems to support paste operations as well.

blocks|key|717561|text|++++++++if+(System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text,+"%5E[a-zA-Z]%2B$"))
++++++++{+
++++++++}
++++++++else
++++++++{
++++++++++++textBox1.Text+=+textBox1.Text.Remove(textBox1.Text.Length+-+1);
++++++++++++MessageBox.Show("Enter+only+Alphabets");


++++++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|717562|请试试这个|unstyled|717563|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code> if (System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, "^[a-zA-Z]+$"))
 { 
 }
 else
 {
 textBox1.Text = textBox1.Text.Remove(textBox1.Text.Length - 1);
 MessageBox.Show("Enter only Alphabets");


 }
</code></pre>

Please Try this

blocks|key|501638|text|将Text_KeyPress事件中的代码编写为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|501639|+private+void+textBox1_KeyPress(object+sender,+KeyPressEventArgs+e)
++++{

++++++++if+(!char.IsLetter(e.KeyChar))
++++++++{
++++++++++++e.Handled+=+true;
++++++++}
++++}|code-block|syntax|javascript|501640|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|$]]

Write Code in Text_KeyPress Event as

<pre><code> private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
 {

 if (!char.IsLetter(e.KeyChar))
 {
 e.Handled = true;
 }
 }
</code></pre>

blocks|key|501644|text|private+void+textbox1_KeyDown_1(object+sender,+KeyEventArgs+e)
{
++++if+(e.Key+>=+Key.A+&&+e.Key+<=+Key.Z)
++++{
++++}
++++else
++++{
+++++++e.Handled+=+true;
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|501645|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>private void textbox1_KeyDown_1(object sender, KeyEventArgs e)
{
 if (e.Key &gt;= Key.A &amp;&amp; e.Key &lt;= Key.Z)
 {
 }
 else
 {
 e.Handled = true;
 }
}
</code></pre>

blocks|key|501663|text|private+void+textBox2_KeyPress(object+sender,+KeyPressEventArgs+e)
++++++++{
++++++++++++if+(e.KeyChar+>=+'0'+&&+e.KeyChar+<=+'9')
++++++++++++++++e.Handled+=+true;
++++++++++++else
++++++++++++++++e.Handled+=+false;
++++++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|501664|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>private void textBox2_KeyPress(object sender, KeyPressEventArgs e)
 {
 if (e.KeyChar &gt;= '0' &amp;&amp; e.KeyChar &lt;= '9')
 e.Handled = true;
 else
 e.Handled = false;
 }
</code></pre>

blocks|key|501674|text|这个运行得非常好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|501675|+private+void+manufacturerOrSupplierTextBox_KeyPress(object+sender,+KeyPressEventArgs+e)
++++{
++++++++if+(char.IsControl(e.KeyChar)+%7C%7C+char.IsLetter(e.KeyChar))
++++++++{
++++++++++++return;
++++++++}
++++++++e.Handled+=+true;
++++}|code-block|syntax|javascript|501676|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 one is working absolutely fine...

<pre><code> private void manufacturerOrSupplierTextBox_KeyPress(object sender, KeyPressEventArgs e)
 {
 if (char.IsControl(e.KeyChar) || char.IsLetter(e.KeyChar))
 {
 return;
 }
 e.Handled = true;
 }
</code></pre>

blocks|key|501687|text|private+void+textBox1_KeyPress(object+sender,+KeyPressEventArgs+e)
++++{
++++++if+(!char.IsControl(e.KeyChar)+&&+!char.IsLetter(e.KeyChar)+&&
+++++++++(e.KeyChar+!='.'))
++++++++{+
++++++++++e.Handled+=+true;
++++++++++MessageBox.Show("Only+Alphabets");
++++++++}
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|501688|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>private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
 {
 if (!char.IsControl(e.KeyChar) &amp;&amp; !char.IsLetter(e.KeyChar) &amp;&amp;
 (e.KeyChar !='.'))
 { 
 e.Handled = true;
 MessageBox.Show("Only Alphabets");
 }
 }
</code></pre>

blocks|key|501731|text|尝尝这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|501732|++++++++++++private+void+tbCustomerName_KeyPress(object+sender,+KeyPressEventArgs+e)
++++{
++++++++e.Handled+=+!(char.IsLetter(e.KeyChar)+%7C%7C+e.KeyChar+==+(char)Keys.Back%7C%7Ce.KeyChar==(char)Keys.Space);
++++}|code-block|syntax|javascript|501733|它也允许空格|501734|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|$]]

Try This

<pre><code> private void tbCustomerName_KeyPress(object sender, KeyPressEventArgs e)
 {
 e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back||e.KeyChar==(char)Keys.Space);
 }
</code></pre>

It Allows White Spaces Too

blocks|key|717733|text|您可以尝试跟踪在按键事件发生时发出警报的代码|type|unstyled|depth|inlineStyleRanges|entityRanges|data|717734|private+void+tbOwnerName_KeyPress(object+sender,+KeyPressEventArgs+e)
++++{

++++++++//===================to+accept+only+charactrs+&+space/backspace=============================================

++++++++if+(e.Handled+=+!(char.IsLetter(e.KeyChar)+%7C%7C+e.KeyChar+==+(char)Keys.Back+%7C%7C+e.KeyChar+==+(char)Keys.Space))
++++++++{
++++++++++++e.Handled+=+true;
++++++++++++base.OnKeyPress(e);
++++++++++++MessageBox.Show("enter+characters+only");
++++++++}|code-block|syntax|javascript|717735|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 try following code that alert at the time of key press event

<pre><code>private void tbOwnerName_KeyPress(object sender, KeyPressEventArgs e)
 {

 //===================to accept only charactrs &amp; space/backspace=============================================

 if (e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back || e.KeyChar == (char)Keys.Space))
 {
 e.Handled = true;
 base.OnKeyPress(e);
 MessageBox.Show("enter characters only");
 }
</code></pre>

blocks|key|501813|text|这是我的解决方案，它按计划工作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|501814|string+errmsg+=+"ERROR+:+Wrong+input";
ErrorLbl.Text+=+errmsg;

if+(e.Handled+=+!(char.IsLetter(e.KeyChar)+%7C%7C+e.KeyChar+==+(char)Keys.Back+%7C%7C+e.KeyChar+==+(char)Keys.Space))
{
++ErrorLbl.Text+=+"ERROR+:+Wrong+input";
}
else+ErrorLbl.Text+=+string.Empty;
if+(ErrorLbl.Text+==+errmsg)
{
++Nametxt.Text+=+string.Empty;
}|code-block|syntax|javascript|501815|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|$]]

Here is my solution and it works as planned:

<pre><code>string errmsg = "ERROR : Wrong input";
ErrorLbl.Text = errmsg;

if (e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back || e.KeyChar == (char)Keys.Space))
{
 ErrorLbl.Text = "ERROR : Wrong input";
}
else ErrorLbl.Text = string.Empty;
if (ErrorLbl.Text == errmsg)
{
 Nametxt.Text = string.Empty;
}
</code></pre>

blocks|key|501822|text|尝试在textbox的KeyPress事件中执行以下代码|type|unstyled|depth|inlineStyleRanges|entityRanges|data|501823|if+(char.IsLetter(e.KeyChar)+==+false++&+
++++++++Convert.ToString(e.KeyChar)+!=+Microsoft.VisualBasic.Constants.vbBack)
++++++++++++e.Handled+=+true|code-block|syntax|javascript|501824|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 following code in KeyPress event of textbox

<pre><code>if (char.IsLetter(e.KeyChar) == false &amp; 
 Convert.ToString(e.KeyChar) != Microsoft.VisualBasic.Constants.vbBack)
 e.Handled = true
</code></pre>

blocks|key|717829|text|此解决方案使用正则表达式，不允许将无效字符粘贴到文本框中，并保持光标位置。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|717830|using+System.Text.RegularExpressions;

int+CursorWas;
string+WhatItWas;

private+void+textBox1_Enter(object+sender,+EventArgs+e)
++++{
++++++++WhatItWas+=+textBox1.Text;
++++}

private+void+textBox1_TextChanged(object+sender,+EventArgs+e)
++++{
++++++++if+(Regex.IsMatch(textBox1.Text,+"%5E[a-zA-Z+]*$"))
++++++++{
++++++++++++WhatItWas+=+textBox1.Text;
++++++++}
++++++++else
++++++++{
++++++++++++CursorWas+=+textBox1.SelectionStart+==+0+?+0+:+textBox1.SelectionStart+-+1;
++++++++++++textBox1.Text+=+WhatItWas;
++++++++++++textBox1.SelectionStart+=+CursorWas;
++++++++}
++++}|code-block|syntax|javascript|717831|注意:+textBox1_TextChanged递归调用。|717832|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 solution uses regular expressions, does not allow invalid characters to be pasted into the text box and maintains the cursor position.

<pre><code>using System.Text.RegularExpressions;

int CursorWas;
string WhatItWas;

private void textBox1_Enter(object sender, EventArgs e)
 {
 WhatItWas = textBox1.Text;
 }

private void textBox1_TextChanged(object sender, EventArgs e)
 {
 if (Regex.IsMatch(textBox1.Text, "^[a-zA-Z ]*$"))
 {
 WhatItWas = textBox1.Text;
 }
 else
 {
 CursorWas = textBox1.SelectionStart == 0 ? 0 : textBox1.SelectionStart - 1;
 textBox1.Text = WhatItWas;
 textBox1.SelectionStart = CursorWas;
 }
 }
</code></pre>

Note: textBox1_TextChanged recursive call.

blocks|key|501892|text|只要有字符限制，如果不是C或L，对错误消息提示的任何建议都可以很好地工作|type|unstyled|depth|inlineStyleRanges|entityRanges|data|501893|Private+Sub+TXTBOX_TextChanged(sender+As+System.Object,+e+As+System.EventArgs)+Handles+TXTBOX.TextChanged

++++++++Dim+allowed+As+String+=+"C,L"
++++++++For+Each+C+As+Char+In+TXTBOX.Text
++++++++++++If+allowed.Contains(C)+=+False+Then

++++++++++++++++TXTBOX.Text+=+TXTBOX.Text.Remove(TXTBOX.SelectionStart+-+1,+1)
++++++++++++++++TXTBOX.Select(TXTBOX.Text.Count,+0)

++++++++++++End+If

++++++++Next
++++++
++++End+Sub|code-block|syntax|javascript|501894|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 works fine as far as characters restriction, Any suggestions on error msg prompt with my code if it's not C OR L
<pre><code>Private Sub TXTBOX_TextChanged(sender As System.Object, e As System.EventArgs) Handles TXTBOX.TextChanged

 Dim allowed As String = &quot;C,L&quot;
 For Each C As Char In TXTBOX.Text
 If allowed.Contains(C) = False Then

 TXTBOX.Text = TXTBOX.Text.Remove(TXTBOX.SelectionStart - 1, 1)
 TXTBOX.Select(TXTBOX.Text.Count, 0)

 End If

 Next
 
 End Sub
</code></pre>

blocks|key|717913|text|对我来说很有效，尽管不是最简单的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|717914|private+void+Alpha_Click(object+sender,+EventArgs+e)
++++++++{
++++++++++++int+count+=+0;
++++++++++++foreach+(char+letter+in+inputTXT.Text)
++++++++++++{
++++++++++++++++if+(Char.IsLetter(letter))
++++++++++++++++{
++++++++++++++++++++count%2B%2B;
++++++++++++++++}
++++++++++++++++else
++++++++++++++++{
++++++++++++++++++++count+=+0;
++++++++++++++++}
++++++++++++}
++++++++++++if+(count+!=+inputTXT.Text.Length)
++++++++++++{
++++++++++++++++errorBox.Text+=+"The+input+text+must+contain+only+alphabetic+characters";
++++++++++++}
++++++++++++else
++++++++++++{
++++++++++++++++errorBox.Text+=+"";
++++++++++++}
++++++++}|code-block|syntax|javascript|717915|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 for me, even though not the simplest one.
<pre><code>private void Alpha_Click(object sender, EventArgs e)
 {
 int count = 0;
 foreach (char letter in inputTXT.Text)
 {
 if (Char.IsLetter(letter))
 {
 count++;
 }
 else
 {
 count = 0;
 }
 }
 if (count != inputTXT.Text.Length)
 {
 errorBox.Text = &quot;The input text must contain only alphabetic characters&quot;;
 }
 else
 {
 errorBox.Text = &quot;&quot;;
 }
 }
</code></pre>

How can I make a <code>TextBox</code> only accept alphabetic characters with spaces?

How to make a TextBox accept only alphabetic characters?

如何使TextBox只接受带空格的字母字符？

问如何让TextBox只接受字母字符？
EN

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问如何让TextBox只接受字母字符？
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