文本框的边框未显示在GroupBox上

Question

I use this code to change the color of the border of a textbox to red.

private void Form1_Paint(object sender, PaintEventArgs e) {
      e.Graphics.DrawRectangle(new Pen(Brushes.Red, 3), 
        tb.Location.X-1, tb.Location.Y-1, tb.ClientRectangle.Width+ 5, 
        tb.ClientRectangle.Height + 5);
}

This works on a textbox that is directly on the Form but not when the textbox is in a groupbox. How should i do that ?

Answer 1

The form's Paint event cannot scribble on the group box, it has its own window. Windows are prevented from painting on each other.

You'll need to use the group box' Paint event.