[c#] How to make a TextBox accept only alphabetic characters?

How can I make a TextBox only accept alphabetic characters with spaces?

You can try by handling the KeyPress event for the textbox

void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back);
}

Additionally say allow backspace in case you want to remove some text, this should work perfectly fine for you

EDIT

The above code won't work for paste in the field for which i believe you will have to use TextChanged event but then it would be a bit more complicated with you having to remove the incorrect char or highlight it and place the cursor for the user to make the correction Or maybe you could validate once the user has entered the complete text and tabs off the control.

private void textbox1_KeyDown_1(object sender, KeyEventArgs e)
{
    if (e.Key >= Key.A && e.Key <= Key.Z)
    {
    }
    else
    {
       e.Handled = true;
    }
}

you can try following code that alert at the time of key press event

private void tbOwnerName_KeyPress(object sender, KeyPressEventArgs e)
    {

        //===================to accept only charactrs & 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");
        }

Write Code in Text_KeyPress Event as

 private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
    {

        if (!char.IsLetter(e.KeyChar))
        {
            e.Handled = true;
        }
    }

private void textBox2_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar >= '0' && e.KeyChar <= '9')
                e.Handled = true;
            else
                e.Handled = false;
        }

works for me, even though not the simplest one.

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 = "The input text must contain only alphabetic characters";
            }
            else
            {
                errorBox.Text = "";
            }
        }

This solution uses regular expressions, does not allow invalid characters to be pasted into the text box and maintains the cursor position.

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;
        }
    }

Note: textBox1_TextChanged recursive call.

Here is my solution and it works as planned:

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;
}

This works fine as far as characters restriction, Any suggestions on error msg prompt with my code if it's not C OR L

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

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

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;
    }

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.

        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");


        }

Please Try this

Try This

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

It Allows White Spaces Too

This one is working absolutely fine...

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

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");
        }
    }

Try following code in KeyPress event of textbox

if (char.IsLetter(e.KeyChar) == false  & 
        Convert.ToString(e.KeyChar) != Microsoft.VisualBasic.Constants.vbBack)
            e.Handled = true