C# - Disabling Keyboard Input into a Textbox

Question

I am trying to disable all keystrokes entered into a text box except the following:

0 1 2 3 4 5 6 7 8 9 . (so all keys except the numbers and the '.' should be disabled)

Right now I have the following code but it only checks to see if a letter was entered as the first value (not to mention its really sloppy):

    private void yDisplacementTextBox_TextChanged(object sender, EventArgs e)
    {
         if (yDisplacementTextBox.Text.ToUpper() == "A" || yDisplacementTextBox.Text.ToUpper() == "B" || yDisplacementTextBox.Text.ToUpper() == "C" ||
             yDisplacementTextBox.Text.ToUpper() == "D" || yDisplacementTextBox.Text.ToUpper() == "E" || yDisplacementTextBox.Text.ToUpper() == "F" || 
             yDisplacementTextBox.Text.ToUpper() == "G" || yDisplacementTextBox.Text.ToUpper() == "H" || yDisplacementTextBox.Text.ToUpper() == "I" ||
             yDisplacementTextBox.Text.ToUpper() == "J" || yDisplacementTextBox.Text.ToUpper() == "K" || yDisplacementTextBox.Text.ToUpper() == "L" ||
             yDisplacementTextBox.Text.ToUpper() == "M" || yDisplacementTextBox.Text.ToUpper() == "N" || yDisplacementTextBox.Text.ToUpper() == "O" ||
             yDisplacementTextBox.Text.ToUpper() == "P" || yDisplacementTextBox.Text.ToUpper() == "Q" || yDisplacementTextBox.Text.ToUpper() == "R" ||
             yDisplacementTextBox.Text.ToUpper() == "S" || yDisplacementTextBox.Text.ToUpper() == "T" || yDisplacementTextBox.Text.ToUpper() == "U" ||
             yDisplacementTextBox.Text.ToUpper() == "V" || yDisplacementTextBox.Text.ToUpper() == "W" || yDisplacementTextBox.Text.ToUpper() == "X" ||
             yDisplacementTextBox.Text.ToUpper() == "Y" || yDisplacementTextBox.Text.ToUpper() == "Z")
        {
            MessageBox.Show("Please enter a numeric value for the Y Displacement.", "Y Displacement: Numbers Only Error",
                       MessageBoxButtons.OK, MessageBoxIcon.Warning);
        }
    }

---

Is there anyway to have it so when pressed, all of the keys on the keyboard (except the numbers and the period button) do not register (or disables) the actual value of the key and inputs nothing?

Answer 1

Use textBox1.KeyPress += textBox1_KeyPress

This code only allowing numbers and . and the backspace.

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if ((e.KeyChar > (char)Keys.D9 || e.KeyChar < (char)Keys.D0) && e.KeyChar != (char)Keys.Back && e.KeyChar != '.')
    { 
        e.Handled = true; 
    }
    //Edit: Alternative
    if (!char.IsDigit(e.KeyChar) && e.KeyChar != (char)Keys.Back && e.KeyChar != '.')
    {
        e.Handled = true;
    }
}