Question

Possible Duplicate:
“ResizeEnd” equivalent for usercontrols

I feel stupid, but I can’t find a solution to a problem that I think it’s easy.
I have a user control that (basically) shows an image drawing it during onPaint stage:

protected override void OnPaint(PaintEventArgs e)
{
    if (img != null)
        e.Graphics.DrawImage(img, ...);
}

When user control is resized, it must perform many actions and one is (given a particular condition) resize image to fit width or height, etc…
Image showed can be “heavy”, so when user start resizing and moves mouse, the result is a sort of slow movement that’s not good for end user.
So I’m wondering if there are windows messages reporting me that the resize operation is starting or completed: if so I can stop redrawing when resize starts and repaint image when resize ends.
Thanks to everybody

EDITED:
I tried this:

protected override void WndProc(ref Message m)
{
    const int WM_ENTERSIZEMOVE = 0x0231;
    const int WM_EXITSIZEMOVE = 0x0232;
    switch (m.Msg)
    {
        case WM_ENTERSIZEMOVE: resizing = true; break;
        case WM_EXITSIZEMOVE: resizing = false; break;
    }
}

but those messages are never called 🙁

Answer 1

I post an answer after a long investigation.
First of all I want to thank everybody for your contribution, because your suggestions led me to the right way. Thanks to @Hans Passant too, because his solution on this post is an important piece.

THE PROBLEM:

• assume we have a usercontrol named innCnt (inner control) contained in another usercontrol named outCnt (outer control), which in turn should be placed in a form we don’t develop (so we can’t edit its source)
• assume we have to catch the EndResize event in innCnt

CONTRIBUTES:

• Using PreProcessMessage or overriding WndProc (thanks to @Cipi):
  I tried these solutions, but I don’t receive WM_ENTERSIZEMOVE and WM_EXITSIZEMOVE messages from Windows
• Trap MouseDown and OnResize events (thanks to @Cipi):
  It could be ok, but that logic should be moved on outCnt because innCnt could not receive MouseDown if user is resizing out control or form.
  Anyway I don’t like too much this solution
• In the Load event of innCnt, hook event handlers to the control’s form’s events (thanks to @hometoast and @pikzen):
  I tried this solution (and the one provided by @Hans here) but this doesn’t work because when innCnt is loaded, even in if not in DesignMode, his parent is a part of outCnt, whose parent is null because not ready set!!

SOLUTION:
Basicly I had to move @Hans logic inside outCnt but not in Load event, because even here parent is still null!

public class OuterControl
{
    protected override void OnParentChanged(EventArgs e)
    {
        if (!this.DesignMode)
        {
            Form form = this.FindForm();
            if (form != null)
            {
                form.ResizeBegin += (s, ea) =>innerCnt.Resizing = true;
                form.ResizeEnd += (s, ea) => innerCnt.Resizing = false;
            }
        }
        base.OnParentChanged(e);
    }
}

public class InnerControl
{
    private bool resizing = false;

    public bool Resizing { 
        get { return resizing; }; 
        set {
            resizing = value;
            if (!resizing) {
                // Resizing is just finished:
                // let's do what we need
            }
        }
    }

    protected override void OnResize(EventArgs e)
    {
        if (Resizing)
        {
            base.OnResize(e);
            return;
        }
        else
        {
            // Perform resizing actions
        }
    }
}

KNOWN PROBLEMS:
I’m quite sure that if outCnt is placed inside another usercontrol, solution provided won’t work…