Textbox BackColor不会改变

Question

Can anyone explain why this code is not working?

 protected override void OnMouseDoubleClick(MouseEventArgs e)
        {
            if (this.BackColor == Color.White)
            {
                this.BackColor = Color.Yellow;

            }
            else
            {
                this.BackColor = Color.White;
            }
                base.OnMouseDoubleClick(e);
        }

It worked few times, but mostly does not work. When i remove the "if" part it works every time, and when i replace "this.BackColor = Color.Yellow" with some other code it also works. Would be very grateful if some could tell what am i doing wrong.

Answer 1

It doesn't work only on first double click (it works but sets the color to White not Yellow as you presumably expect) because == operator compares Name and ARGB properties of the color, not only the ARGB property. Although on first doubleclick ARGB values are the same (ARGB=(255, 255, 255, 255)) , names are not because the initial BackColor property has the name "Window" and the Color.White has the value of the Name property "White" and therefore they are not the same. You could check that yourself in debugger.

To avoid the problem you could rewrite your code as follows:

protected override void OnMouseDoubleClick(MouseEventArgs e)
{
      //compare ARGB values
      if (this.BackColor.ToArgb() == Color.White.ToArgb())
      {
           this.BackColor = Color.Yellow;

      }
      else
      {
           this.BackColor = Color.White;
      }
      base.OnMouseDoubleClick(e);
}