使 Winform 中的所有控件无效会导致无限调用 OnPaint 方法

Question

I have two Extented controls. First one is called LiveControl which is inherited from PictureBox which have Resizing,Rotation, Move,... Methods. Second one is called DrawPanel which is inherited from Panel which is meant to be the parent for several LiveControl s.

I did several things to reduce filckering and also leaving trails when one LiveControl moved over another. and finally I achieved it even better than I expected with the following codes in LiveControl :

MouseUp += (s, e) =>
{
    foreach (Control c in Parent.Controls.OfType<LiveControl>())
        c.Refresh();
};
MouseMove += (s, e) =>
{
    if (e.Button == MouseButtons.Left)
    {
        Control x = (Control)s;
        x.SuspendLayout();
        x.Location = new Point(x.Left + e.X - cur.X, x.Top + e.Y - cur.Y);
        x.ResumeLayout();
        foreach (Control c in Parent.Controls.OfType<LiveControl>())
            c.Update();
    }
};

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    foreach (Control c in Parent.Controls.OfType<LiveControl>())                
        c.Invalidate();                    
}

But the problem is that as in the above code, each LiveControl 's OnPaint invalidates all of the LiveControl s, it causes infinite calls of OnPaint which causes problems for other controls on the form (they work very slow with delays).

To solve this I edited the code for OnPaint like this:

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    if (!((DrawPanel)Parent).Invalidating)
    {
        ((DrawPanel)Parent).Invalidating = true;
        ((DrawPanel)Parent).InvalidatedCount = 0;
        foreach (Control c in Parent.Controls.OfType<LiveControl>())                
            c.Invalidate();            
    }
    else
    {
        ((DrawPanel)Parent).InvalidatedCount++;
        if (((DrawPanel)Parent).InvalidatedCount == ((DrawPanel)Parent).Controls.OfType<LiveControl>().Count())
        { 
            ((DrawPanel)Parent).InvalidatedCount = 0; ((DrawPanel)Parent).Invalidating = false;  
        }
    }
}

But the OnPaint method is still being called nonstop. Does anybody has any idea how to solve this?

Answer 1

Invalidate triggers Paint . Calling Invalidate in Paint is an endless-loop. Don't do that!

Flicker will go away if all controls that show it have DoubleBuffering on. Note that to turn on DoublBuffering you may need to subclass some of them, like Panels , FlowLayoutPanels or DGVs .. In fact only Form exposes it and only PictureBox has it on by default.

You also need to make sure all unnecessary Invalidates are eliminated. - Usually you need Invalidate only when data you need in drawing have changed . I don't see any drawing in your code at all. Otherwise you sometimes may need to call Refresh to eliminate tearing , ie 'tails' or 'traces'.

Answer 2

I would not deal with OnPaint at all. I you want to make custom paint do it in the Paint event.

You should never call Invalidate() in a paint update situation. If you have problems with flicker have you tried to set DoubleBuffered to true on your custom controls and container?

If you invalidate DrawPanel by calling DrawPanel.Invalidate() one override has a flag called bool invalidateChildren . Have you tried to set that to true?

Hope this will help.