Converting tabs into spaces in a RichTextBox

Question

I have a WinForms application with a RichTextBox control on the form. Right now, I have the AcceptsTabs property set to true so that when Tab<

Answer 1

Add a new class to override your RichTextBox:

class MyRichTextBox : RichTextBox
{
    protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
    {
        if(keyData == Keys.Tab)
        {
            SelectionLength = 0;
            SelectedText = new string(' ', 4);
            return true;
        }

        return base.ProcessCmdKey(ref msg, keyData);
    }
}

You can then drag your new control on to the Design view of your form:

Note: unlike with @LarsTec's answer, setting AcceptsTab is not required here.

Answer 2

With the AcceptsTab property set to true, just try using the KeyPress event:

void richTextBox1_KeyPress(object sender, KeyPressEventArgs e) {
  if (e.KeyChar == (char)Keys.Tab) {
    e.Handled = true;
    richTextBox1.SelectedText = new string(' ', 4);
  }
}

Based on your comments regarding adding spaces up to every fourth character, you can try something like this:

void richTextBox1_KeyPress(object sender, KeyPressEventArgs e) {
  if (e.KeyChar == (char)Keys.Tab) {
    e.Handled = true;
    int numSpaces = 4 - ((richTextBox1.SelectionStart - richTextBox1.GetFirstCharIndexOfCurrentLine()) % 4);
    richTextBox1.SelectedText = new string(' ', numSpaces);

  }
}