Pass-through mouse events to parent control

Question

Environment: .NET Framework 2.0, VS 2008.

I am trying to create a subclass of certain .NET controls (label, panel) that will pass through certain mouse events (MouseDown, MouseMove, MouseUp) to its parent control (or alternatively to the top-level form). I can do this by creating handlers for these events in instances of the standard controls, e.g.:

public class TheForm : Form
{
    private Label theLabel;

    private void InitializeComponent()
    {
        theLabel = new Label();
        theLabel.MouseDown += new MouseEventHandler(theLabel_MouseDown);
    }

    private void theLabel_MouseDown(object sender, MouseEventArgs e)
    {
        int xTrans = e.X + this.Location.X;
        int yTrans = e.Y + this.Location.Y;
        MouseEventArgs eTrans = new MouseEventArgs(e.Button, e.Clicks, xTrans, yTrans, e.Delta);
        this.OnMouseDown(eTrans);
    }
}

I cannot move the event handler into a subclass of the control, because the methods that raise the events in the parent control are protected and I don't have a qualifier for the parent control:

Cannot access protected member System.Windows.Forms.Control.OnMouseDown(System.Windows.Forms.MouseEventArgs) via a qualifier of type System.Windows.Forms.Control; the qualifier must be of type TheProject.NoCaptureLabel (or derived from it).

I am looking into overriding the WndProc method of the control in my sub-class, but hopefully someone can give me a cleaner solution.

Answer 1

Yes. After a lot of searching, I found the article "Floating Controls, tooltip-style", which uses WndProc to change the message from WM_NCHITTEST to HTTRANSPARENT, making the Control transparent to mouse events.

To achieve that, create a control inherited from Label and simply add the following code.

protected override void WndProc(ref Message m)
{
    const int WM_NCHITTEST = 0x0084;
    const int HTTRANSPARENT = (-1);

    if (m.Msg == WM_NCHITTEST)
    {
        m.Result = (IntPtr)HTTRANSPARENT;
    }
    else
    {
        base.WndProc(ref m);
    }
}

I have tested this in Visual Studio 2010 with .NET Framework 4 Client Profile.