Cleaning DrawRectangle on Windows Forms

Question

I draw a rectangle that sleeps for a few milliseconds - then I want to clear the rectangle, but I cannot figure out how to do this. (The rectangle sits above the graphics, so I can’t just cover it with another rectangle)

                graphics.DrawRectangle(p, innerRectangle)
                System.Threading.Thread.Sleep(75)
                Next I want to clear the rectange...

Answer 1

You need to redraw the graphics (or at least part of it below the rectangle). If this is a picture window or something similar, use Invaldiate () to force the redraw.

Answer 2

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public void ShowRectangleBriefly(Control ctl, Rectangle rect)
{
    Image toRestore = DrawRectangle(ctl, rect);
    ThreadPool.QueueUserWorkItem((WaitCallback)delegate
    {
        Thread.Sleep(500);
        this.Invoke(new Action<Control, Rectangle, Image>(RestoreBackground), ctl, rect, toRestore);
    });
}

private void RestoreBackground(Control ctl, Rectangle rect, Image image)
{
    using (Graphics g = ctl.CreateGraphics())
    {
        g.DrawImage(image, rect.Top, rect.Left, image.Width, image.Height);
    }
    image.Dispose();
}

private Image DrawRectangle(Control ctl, Rectangle rect)
{
    Bitmap tempBmp = new Bitmap(rect.Width + 1, rect.Height + 1);
    using (Graphics g = Graphics.FromImage(tempBmp))
    {
        g.CopyFromScreen(ctl.PointToScreen(new Point(rect.Top, rect.Left)), new Point(0, 0), tempBmp.Size);
    }

    using (Graphics g = this.CreateGraphics())
    {
        g.DrawRectangle(Pens.Red, rect);
    }
    return tempBmp;
}

Answer 3

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Answer 4

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SelectionBox box = new SelectionBox();
box.Location = location;
box.Size = size;
box.Visible = true;

, , , :

box.Visible = false;

The panel class is made with transparency to ensure that overlay graphics do not hide other window contents.

  [System.ComponentModel.DesignerCategory("Code")]
  public class SelectionBox : Panel
  {
    protected override void OnPaint(PaintEventArgs e)
    {
      const int penWidth = 2;
      int offset = penWidth - 1;
      using (Pen pen = new Pen(Color.Red, 2))
        e.Graphics.DrawRectangle(pen, offset, offset, 
          ClientSize.Width - offset - 1, ClientSize.Height - offset - 1);
    }

    protected override CreateParams CreateParams
    {
      get
      {
        CreateParams cp = base.CreateParams;
        cp.ExStyle |= 0x00000020; // WS_EX_TRANSPARENT
        return cp;
      }
    }
  }