Mouse Wheel Event (C#)

Question

I can't get the Mouse Wheel event in the main form.

As a demo I came up with a simple example:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        this.panel1.MouseWheel += new MouseEventHandler(panel1_MouseWheel);
        this.panel1.MouseMove += new MouseEventHandler(panel1_MouseWheel);

        Form2 f2 = new Form2();
        f2.Show(this);
    }

    private void panel1_MouseWheel(object sender, MouseEventArgs e)
    {
        if(e.Delta != 0)
        Console.Out.WriteLine(e.Delta);
    }
}

public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();

        this.MouseMove += new MouseEventHandler(Form2_MouseMove);
        this.MouseWheel += new MouseEventHandler(Form2_MouseMove);
    }

    private void Form2_MouseMove(object sender, MouseEventArgs e)
    {
        if(e.Delta != 0)
            Console.Out.WriteLine(e.Delta);
    }
}

I get the mouse wheel event in Form2 but not Form1 any ideas?

Cheers,

James

Solution 1

I suspect the OP wants to get scroll events when just the mouse is hovering over the panel even though the panel does not have the focus.

A way to accomplish this behaviour is explained here:

http://social.msdn.microsoft.com/forums/en-US/winforms/thread/eb922ed2-1036-41ca-bd15-49daed7b637c/

and here:

http://social.msdn.microsoft.com/forums/en-US/winforms/thread/6bfb9287-986d-4c60-bbcc-23486e239384/

One of the code snippets taken from the linked forum:

using System;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowsApplication1 {
  public partial class Form1 : Form, IMessageFilter {
    public Form1() {
      InitializeComponent();
      Application.AddMessageFilter(this);
    }

    public bool PreFilterMessage(ref Message m) {
      if (m.Msg == 0x20a) {
        // WM_MOUSEWHEEL, find the control at screen position m.LParam
        Point pos = new Point(m.LParam.ToInt32() & 0xffff, m.LParam.ToInt32() >> 16);
        IntPtr hWnd = WindowFromPoint(pos);
        if (hWnd != IntPtr.Zero && hWnd != m.HWnd && Control.FromHandle(hWnd) != null) {
          SendMessage(hWnd, m.Msg, m.WParam, m.LParam);
          return true;
        }
      }
      return false;
    }

    // P/Invoke declarations
    [DllImport("user32.dll")]
    private static extern IntPtr WindowFromPoint(Point pt);
    [DllImport("user32.dll")]
    private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);
  }
}

This code will basically intercept all wm_mousewheel events and redirect them to the control the mouse is currently hovering over. The panel doesn't need to have the focus anymore to receive the wheel events.

Solution 2

Your problem arises from the fact that form1 has focus, not panel1. ...which ofcourse means that it is form1's events that will be fired, not panel1's events.

I recreated your scenario with the following changes to the constructor in Form1 and verified that it fires the scroll wheel event.

public Form1()
{
        InitializeComponent(); 

        /*  --- Old code that don't work ---
            this.panel1.MouseWheel += new MouseEventHandler(panel1_MouseWheel);
            this.panel1.MouseMove += new MouseEventHandler(panel1_MouseWheel);
        */

        this.MouseWheel += new MouseEventHandler(panel1_MouseWheel);
        this.MouseMove += new MouseEventHandler(panel1_MouseWheel);

        Form2 f2 = new Form2();
        f2.Show(this);
    }
}

Solution 3

Thanks to @nitrogenycs 's answer, I've wrote a simple generic class to easily address the issue:

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Drawing;

namespace MyNamespace
{
  public class MouseWheelManagedForm : Form, IMessageFilter
  {
    private bool managed;

    public MouseWheelManagedForm () : this (true) {
   }

    public MouseWheelManagedForm (bool start) {
      managed = false;
      if (start)
        ManagedMouseWheelStart();
    }

    protected override void Dispose (bool disposing) {
      if (disposing)
        ManagedMouseWheelStop();
      base.Dispose(disposing);
    }

    /************************************
     * IMessageFilter implementation
     * *********************************/
    private const int WM_MOUSEWHEEL = 0x20a;
    // P/Invoke declarations
    [DllImport("user32.dll")]
    private static extern IntPtr WindowFromPoint (Point pt);
    [DllImport("user32.dll")]
    private static extern IntPtr SendMessage (IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);

    private bool IsChild (Control ctrl) {
      Control loopCtrl = ctrl;

      while (loopCtrl != null && loopCtrl != this)
        loopCtrl = loopCtrl.Parent;

      return (loopCtrl == this);
    }

    public bool PreFilterMessage (ref Message m) {
      if (m.Msg == WM_MOUSEWHEEL) {
        //Ensure the message was sent to a child of the current form
        if (IsChild(Control.FromHandle(m.HWnd))) {
          // Find the control at screen position m.LParam
          Point pos = new Point(m.LParam.ToInt32() & 0xffff, m.LParam.ToInt32() >> 16);

          //Ensure control under the mouse is valid and is not the target control
          //otherwise we'd be trap in a loop.
          IntPtr hWnd = WindowFromPoint(pos);
          if (hWnd != IntPtr.Zero && hWnd != m.HWnd && Control.FromHandle(hWnd) != null) {
            SendMessage(hWnd, m.Msg, m.WParam, m.LParam);
            return true;
          }
        }
      }
      return false;
    }

    /****************************************
     * MouseWheelManagedForm specific methods
     * **************************************/
    public void ManagedMouseWheelStart () {
      if (!managed) {
        managed = true;
        Application.AddMessageFilter(this);
      }
    }

    public void ManagedMouseWheelStop () {
      if (managed) {
        managed = false;
        Application.RemoveMessageFilter(this);
      }
    }

  }
}

From there, you only need to inherit your Form from this class instead of Form for every form you need the MouseWheel to be "managed":

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Windows.Forms;

namespace MyApp
{
  public partial class MyForm : MyNamespace.MouseWheelManagedForm
  {
    public MyForm ()
    {
      InitializeComponent();
    }

  }
}

Hope this will help someone else (than me).