C# Graphics.Clear(Color.Transparent) 不能正常工作？

Question

I'm drawing some graphics on a control area repeatedly, and each time I want to start fresh with a transparent background. So I use:

Graphics graph = control.CreateGraphics();
graph.Clear(Color.Transparent);

However, the graphics area seems to turn black instead of transparent. Any ideas?

Answer 1

I found an alternate way to achieve what I need. I create a new transparent bitmap with the control's dimensions, draw my stuff on it and then use it as a background image for the control:

    Bitmap bitmap = new Bitmap(control.Width, control.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
    bitmap.MakeTransparent();
    Graphics graph = Graphics.FromImage(bitmap);

    //  draw stuff here ...

    control.BackgroundImage = bitmap;
    graph.Dispose();

This works perfectly.

Answer 2

because picturebox has not transparency layer. you could be use transfer bitmap. try this.

        tmp_bmp = new Bitmap(picturebox1.Width, picturebox1.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
         Graphics Canvas = Graphics.FromImage(tmp_bmp);
         picturebox1.Image = tmp_Type;

        Type_Canvas.Clear(Color.Transparent);

Answer 3

This approach worked fine for me:

private void MyCustomControl_Paint(object sender, PaintEventArgs e)
    {
        // Clear background - also works when backcolor is transparent
        InvokePaintBackground(this, e);