Need help with overriding OnKeypress in windows phone 7

[Yayati]

I am using a windows phone 7(mango) and I have made a code in order to restrict textbox input to only digits but it is not working with the wp7 I don’t know where I am going wrong and I think that there is something missing in it but I am not getting it as I am new to C#. So is there anyone who has an idea about it and can help me out with as well. Any suggestion regarding this will be highly appreciated.
protected override void OnKeypress(KeyEventArgs a)

{
base.OnKeyDown(a);

if (char.IsDigit(Convert.ToChar(a.Key)))
{

}
else
{
a.Handled = true;
}
}

[Faizah]

I think that you can try this out:
private void textBox1_Keypress(object sender, KeyEventArgs a) {

if (e.PlatformKeyCode >= 48 && e.PlatformKeyCode <= 57) {
System.Diagnostics.Debug.WriteLine("digit: " + a.Key);
} else {
System.Diagnostics.Debug.WriteLine("letters: " +a.Key);
a.Handled = true;
}


}
Just check it out and then let me know if it works for you.

[AabheerM]

You can try this one as well:
protected override void OnKeypress(KeyEventArgs a)
{
base.OnKeypress(a);

if (a.Key == Key.D0 || a.Key == Key.D1 || a.Key == Key.D2 || a.Key == Key.D3 || a.Key == Key.D4 || a.Key == Key.D5 || a.Key == Key.D6 || a.Key == Key.D7 || a.Key == Key.D8 || a.Key == Key.D9 || a.Key == Key.Decimal)
{
}
else
{
a.Handled = true;
}
}

[Haimi-32]

I have tried this code out but then I will like to inform you that the above codes are not able to stop the keys like !#&$.I think that they have same PlatformKeyCode and the key values as numbers.I just wanted to know that have you found any error in the emulator or something or it is just a problem of the platform. Any help regarding this will be appreciated.