public void Reset(bool visible)
{
num_digits = 0;
pin = 0;
digit1.Text = ""; digit2.Text = ""; digit3.Text = ""; digit4.Text = "";
pin_string = "";
if (numpad == null || numpad_frame == null)
CreateNumpadKeyboard();
else
this.UpdateLayout();
if (visible)
numpad_frame.Visibility = System.Windows.Visibility.Visible;
else
numpad_frame.Visibility = System.Windows.Visibility.Collapsed;
numpad.MoveAlongWith(parent, center);
}