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.

Answer 2

You need to write a public/protected method in your base class which will raise the event for you. Then call this method from the derived class.

OR

Is this what you want?

public class MyLabel : Label {     protected override void OnMouseDown(MouseEventArgs e)     {         base.OnMouseDown(e);         //Do derived class stuff here     } }