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.

Engvall

Answer 1

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 && ...)

Uriel

Just tested it - the comparison against (char)8 does indeed work. – Uriel

Might be better to use '\b' over (char)8. – Campbellbannerman

@AlexHumphrey I think even better is (char)Keys.Back – Shelley

Answer 2

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;

Microeconomics

Answer 3

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;
            }
        }

Taeniacide

Answer 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;
    }
}

Lx

The backspace does rise a keypress event – Shelley

Answer 5

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

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

Correna

Answer 6

From the documentation:

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

Zingaro

In which case the documentation is wrong. I've tested (char)8 from the KeyPress event and it's definitely raised. – Uriel

+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. – Civics

Agreed with Antonio on the prior post and Matt Hamilton above, that despite the doc, the KeyPress event is raised on backspace. – Teflon

Answer 7

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;
     }
  }

Ferrochromium

Answer 8

This Might Help You

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

Pentecost

Answer 9

To Allow only numbers and backspace

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

Ryannryazan

Answer 10

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.

Hearing

Answer 11

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));
    }
}

Borreri

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. – Quinte