KeyPress Event gives wrong value

Question

I made a KeyPress Event and want to allow only Double values (or just digits and comma) so I tried this:

 e.Handled = !(char.IsNumber(e.KeyChar) || e.KeyChar == (char)Keys.Back || e.KeyChar == (char)Keys.Decimal);

But somehow he's got problems with the "Decimal". I'm using a german keyboard and when I try to enter the comma, he does nothing. When I press the "n" key he writes the letter. What is wrong here and how to solve that?

Answer 1

you can restrict the input using keyPress event like so:

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
   char c= e.KeyChar;
   if (!char.IsDigit(c) && !char.IsControl(c))
   {
      e.Handled = true;
    }
}

if we want to extend our restriction condition to accept a certain character (for example ,)

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
  char c= e.KeyChar;
  if (!char.IsDigit(c) && !char.IsControl(c) && c!=',')
  {
    e.Handled = true;
  }
}

To avoid having multiple comma like 222,34545,454 we can do this work around:

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
  char c= e.KeyChar;
  bool comma= textBox1.Text.Contains(','); //true in case comma already inserted

  // accepts only digits, controls and comma
  if (!char.IsDigit(c) && !char.IsControl(c) && c!=',')
  {
    e.Handled = true;
    return;
  }


  // whenever a comma is inserted we check if we already have one
  if (c == ',' && comma)
  {
    e.Handled = true;
  }
}