Question

I think I’m missing something trivial here. I derived simple control directly from Control. I’m overriding OnPaint and painting the rectangle (e.Graphics.DrawRectangle)and a text inside it (e.Graphics.DrawString). I did not override any other members.

It paints itself well when the control is resized to the smaller size, but when it gets resized to the larger size, new area is not repainted properly. As soon as I resize it to the smaller size again, even if by one pixel, everything repaints correctly.

OnPaint gets called properly (with appropriate PaintEventArgs.ClipRectangle set correctly to new area), but the new area is not painted (artifacts appear) anyway.

What am I missing?

EDIT:

Code:

protected override void OnPaint(PaintEventArgs e)
{
    // Adjust control's height based on current width, to fit current text:

    base.Height = _GetFittingHeight(e.Graphics, base.Width);

    // Draw frame (if available):

    if (FrameThickness != 0)
    {
        e.Graphics.DrawRectangle(new Pen(FrameColor, FrameThickness),
            FrameThickness / 2, FrameThickness / 2, base.Width - FrameThickness, base.Height - FrameThickness);
    }

    // Draw string:

    e.Graphics.DrawString(base.Text, base.Font, new SolidBrush(base.ForeColor), new RectangleF(0, 0, base.Width, base.Height));
}

private int _GetFittingHeight(Graphics graphics, int width)
{
    return (int)Math.Ceiling(graphics.MeasureString(base.Text, base.Font, width).Height);
}

Answer 1

Try adding this in your constructor:

public MyControl() {
  this.ResizeRedraw = true;
  this.DoubleBuffered = true;
}

and in your paint event, clear the previous drawing:

protected override void OnPaint(PaintEventArgs e) {
  e.Graphics.Clear(SystemColors.Control);
  // yada-yada-yada
}