How can I accept the backspace key in the keypress event?

Question

This is my code:

private void txtAdd_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!(char.IsLetter(e.KeyChar)) && !(char.IsNumber(e.KeyChar)) && !(char.IsWhiteSpace(e.KeyChar)))
    {
        e.Handled = true;
    }
}

It allows me to enter letters, numbers and spaces but it doesn't allow me to do backspace. Please help me.

score 39 · Answer 1 · answered Jul 28 '09 at 02:59

39

I like to use !Char.IsControl(e.KeyChar) so that all the "control" characters like the backspace key and clipboard keyboard shortcuts are exempted.

If you just want to check for backspace, you can probably get away with:

if (e.KeyChar == (char)8 && ...)

answered Jul 28 '09 at 02:59

Matt Hamilton

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Just tested it - the comparison against (char)8 does indeed work. – Matt Hamilton Jul 28 '09 at 03:01
12

Might be better to use `'\b'` over `(char)8`. – Alex Humphrey Jul 11 '12 at 10:02
12

@AlexHumphrey I think even better is `(char)Keys.Back` – Antonio Sep 23 '15 at 07:40

score 20 · Answer 2 · edited Sep 01 '14 at 10:41

I use the two following segments alot:

This one for restricting a textbox to integer only, but allowing control keys:

if (Char.IsDigit(e.KeyChar)) return;
if (Char.IsControl(e.KeyChar)) return;
e.Handled = true;

This one for restricing a textbox to doubles, allowing one '.' only, and allowing control keys:

if (Char.IsDigit(e.KeyChar)) return;
if (Char.IsControl(e.KeyChar)) return;
if ((e.KeyChar == '.') && ((sender as TextBox).Text.Contains('.') == false)) return;
if ((e.KeyChar == '.') && ((sender as TextBox).SelectionLength == (sender as TextBox).TextLength)) return;
e.Handled = true;

score 7 · Answer 3 · answered Nov 21 '16 at 23:17

You have to add !(char.IsControl(e.KeyChar)) in you sentence and that's it.

private void txtNombre_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!(char.IsLetter(e.KeyChar)) && !(char.IsNumber(e.KeyChar)) && !(char.IsControl(e.KeyChar)) && !(char.IsWhiteSpace(e.KeyChar)))
            {
                e.Handled = true;
            }
        }

score 4 · Answer 4 · answered Aug 05 '13 at 16:07

4

The backspace key does not raised by KeyPress event. So you need to catch it in KeyDown or KeyUp events and set SuppressKeyPress property is true to prevent backspace key change your text in textbox:

private void txtAdd_KeyDown(object sender, KeyEventArgs e)
{
    if (e.KeyCode == Keys.Back)
    {
        e.SuppressKeyPress = true;
    }
}

answered Aug 05 '13 at 16:07

Huy Nguyen

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4

The backspace does rise a keypress event – Antonio Sep 23 '15 at 07:40

score 3 · Answer 5 · answered Feb 21 '20 at 17:23

3

for your problem try this its work for when backspace key pressed

e.KeyChar == ((char)Keys.Back)

answered Feb 21 '20 at 17:23

Sepehr Ariamehr

31
2

score 1 · Answer 6 · answered Jul 28 '09 at 03:17

1

From the documentation:

The KeyPress event is not raised by noncharacter keys; however, the noncharacter keys do raise the KeyDown and KeyUp events.

answered Jul 28 '09 at 03:17

Ed S.

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5

In which case the documentation is wrong. I've tested (char)8 from the KeyPress event and it's definitely raised. – Matt Hamilton Jul 28 '09 at 05:38
+1 I am fully satisfied with Ed S. why using `type casting` when we have `key up` and `key down` events. In normal cases we should avoid `type casting`. we should use `type casting` when we dont have any other alternatives. – Mr_Green Oct 12 '12 at 06:58
Agreed with Antonio on the prior post and Matt Hamilton above, that despite the doc, the KeyPress event is raised on backspace. – David Carr Nov 08 '18 at 23:32

score 0 · Answer 7 · answered Aug 11 '15 at 05:33

private void KeyPressNameSurname(object sender, KeyPressEventArgs e)
 {
     if (char.IsPunctuation(e.KeyChar) || char.IsSymbol(e.KeyChar) || char.IsDigit(e.KeyChar) )
     {
        e.Handled = true;
        myTextBox.Text = "Not Valid";
        myTextBox.Visible = true;
     }
     else
     {
        myTextBox.Visible = false;
     }
  }

score 0 · Answer 8 · answered Mar 25 '21 at 10:00

0

This Might Help You

if(Keys.KeyCode==Keys.Back){
   e.Handled =true;
 }

answered Mar 25 '21 at 10:00

score 0 · Answer 9 · answered Apr 05 '22 at 18:40

0

To Allow only numbers and backspace

private void txt_KeyPress(object sender, KeyPressEventArgs e)
{
   e.Handled = !(char.IsDigit(e.KeyChar) || e.KeyChar == (char)8);
}

answered Apr 05 '22 at 18:40

MaxDNet

108
4

score 0 · Answer 10 · answered Feb 07 '23 at 00:11

While this is a very OLD question some folks may find that the code does not work.
I tried to use this code to capture a BACKSPACE key press inside a RichTextBox
That is using public void rtbInfo_TextChanged(Object sender, EventArgs e)
And Yes without adding this line code the BACKSPACE keypress was never detected

public frmRTB()
    {
        InitializeComponent();
        rtbInfo.KeyPress += rtbInfo_KeyPress;
    }

It seems you need to register the component or shall we say tool.

score -1 · Answer 11 · edited Feb 08 '15 at 21:48

-1

private void Keypressusername(object sender, KeyPressEventArgs e)
{
    e.Handled = !(char.IsLetter(e.KeyChar));
    if (char.IsControl(e.KeyChar))
    {
        e.Handled = !(char.IsControl(e.KeyChar));
    }
    if (char.IsWhiteSpace(e.KeyChar))
    {
        e.Handled = !(char.IsWhiteSpace(e.KeyChar));
    }
}

edited Feb 08 '15 at 21:48

oɔɯǝɹ

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answered Feb 08 '15 at 21:21

naveen kumar

1

While this code sample may possibly answer the question, it would be preferable to include some essential explanation to your answer. As it stands now this answer adds little to no value for future readers. – oɔɯǝɹ Feb 08 '15 at 21:47

How can I accept the backspace key in the keypress event?

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