UserControl: How to add MouseWheel Listener?

Question

I'm creating an UserControl that should react if the mouse is over the control and MouseWheel gets rotated.

Currently i'm doing this as shown here:

    public MyUserControl()
    {
        this.MouseWheel += new MouseEventHandler(MouseWheelHandler);
    }

    private void MouseWheelHandler(object sender, System.Windows.Forms.MouseEventArgs e)
    {
        if (e.Delta > 0)
            incIndex();

        if (e.Delta < 0)
            decIndex();
    }

    protected override void OnMouseEnter(EventArgs e)
    {
        this.Focus();

        base.OnMouseEnter(e);
    }

In fact this works fine, but the problem is the part with the "this.Focus();" as it destroys my forms / applications behaviour.

Is there a better way to achive this?

Answer 1

having the same problem, I finally implemented a mix of both solution by @Paul_Westcott and @nr1. This is a local solution like solution of @Paul_Westcott (only applies to the winforms control that subscribes to). It is multiple monitor safe and MDI safe (overlapping by other windows within the application)

public static class MouseWheelHandlerForWinformsControl
{
    private class MouseWheelMessageFilter : IMessageFilter
    {
        [DllImport("user32.dll")]
        private static extern IntPtr WindowFromPoint(Point pt);

        private readonly Control mCtrl;
        private readonly Action<MouseEventArgs> mOnMouseWheel;

        public MouseWheelMessageFilter(Control ctrl, Action<MouseEventArgs> onMouseWheel)
        {
            mCtrl = ctrl;
            mOnMouseWheel = onMouseWheel;
        }

        public bool PreFilterMessage(ref Message m)
        {
            // handle only mouse wheel messages
            if (m.Msg != 0x20a)
                return false;

            Point mouseAbsolutePosition = new Point(m.LParam.ToInt32());
            Point mouseRelativePosition = mCtrl.PointToClient(mouseAbsolutePosition);

            IntPtr hControlUnderMouse = WindowFromPoint(mouseAbsolutePosition);
            Control controlUnderMouse = Control.FromHandle(hControlUnderMouse);

            if (controlUnderMouse != mCtrl)
                return false;

            MouseButtons buttons = GetMouseButtons(m.WParam.ToInt32());
            int delta = m.WParam.ToInt32() >> 16;

            var e = new MouseEventArgs(buttons, 0, mouseRelativePosition.X, mouseRelativePosition.Y, delta);

            mOnMouseWheel(e);

            return true;
        }

        private static MouseButtons GetMouseButtons(int wParam)
        {
            MouseButtons buttons = MouseButtons.None;

            if(HasFlag(wParam, 0x0001)) buttons |= MouseButtons.Left;
            if(HasFlag(wParam, 0x0010)) buttons |= MouseButtons.Middle;
            if(HasFlag(wParam, 0x0002)) buttons |= MouseButtons.Right;
            if(HasFlag(wParam, 0x0020)) buttons |= MouseButtons.XButton1;
            if(HasFlag(wParam, 0x0040)) buttons |= MouseButtons.XButton2;

            return buttons;
        }

        private static bool HasFlag(int input, int flag)
        {
            return (input & flag) == flag;
        }
    }

    public static void MemorySafeAdd(Control ctrl, Action<MouseEventArgs> onMouseWheel)
    {
        if (ctrl == null || onMouseWheel == null)
            throw new ArgumentNullException();

        var filter = new MouseWheelMessageFilter(ctrl, onMouseWheel);
        Application.AddMessageFilter(filter);
        ctrl.Disposed += (s, e) => Application.RemoveMessageFilter(filter);
    }
}

Once you have added this helper class into your solution, you subscribe a control myControl to the mouse-wheel, in one line, as following:

public void Init() {
    MouseWheelHandlerForWinformsControl.MemorySafeAdd(myControl, OnMouseWheelEvent);
}

void OnMouseWheelEvent(MouseEventArgs args) {
    // do what you need here
}

Answer 2

Paul Westcott's answer works great when using a FlowLayoutPanel. My implementation of MyOnMouseWheel event is:

void MyOnMouseWheel(MouseEventArgs e)
{
    int ChangeIncrement = (this.panel1.VerticalScroll.SmallChange * 4); //Change the 4 to any positive number to scroll more or less one each scroll event.
    if (e.Delta < 0)
    {
        int NewValue = this.panel1.VerticalScroll.Value + ChangeIncrement;
        if (NewValue > this.panel1.VerticalScroll.Maximum)
        {
            this.panel1.VerticalScroll.Value = this.panel1.VerticalScroll.Maximum;
        }
        else
        {
            this.panel1.VerticalScroll.Value = NewValue;
        }
    }
    else if (e.Delta > 0)
    {
        int NewValue = this.panel1.VerticalScroll.Value - ChangeIncrement;
        if (NewValue < this.panel1.VerticalScroll.Minimum)
        {
            this.panel1.VerticalScroll.Value = this.panel1.VerticalScroll.Minimum;
        }
        else
        {
            this.panel1.VerticalScroll.Value = NewValue;
        }
    }
    this.panel1.PerformLayout();
}

Answer 3

Just a slight variation on the solution that has already been published, in order to not have to use P/Invoke.

public static class MouseWheelHandler
{
    public static void Add(Control ctrl, Action<MouseEventArgs> onMouseWheel)
    {
        if (ctrl == null || onMouseWheel == null)
            throw new ArgumentNullException();

        var filter = new MouseWheelMessageFilter(ctrl, onMouseWheel);
        Application.AddMessageFilter(filter);
        ctrl.Disposed += (s, e) => Application.RemoveMessageFilter(filter);
    }

    class MouseWheelMessageFilter
        : IMessageFilter
    {
        private readonly Control _ctrl;
        private readonly Action<MouseEventArgs> _onMouseWheel;

        public MouseWheelMessageFilter(Control ctrl, Action<MouseEventArgs> onMouseWheel)
        {
            _ctrl = ctrl;
            _onMouseWheel = onMouseWheel;
        }

        public bool PreFilterMessage(ref Message m)
        {
            var parent = _ctrl.Parent;
            if (parent != null && m.Msg == 0x20a) // WM_MOUSEWHEEL, find the control at screen position m.LParam
            {
                var pos = new Point(m.LParam.ToInt32() & 0xffff, m.LParam.ToInt32() >> 16);

                var clientPos = _ctrl.PointToClient(pos);

                if (_ctrl.ClientRectangle.Contains(clientPos)
                 && ReferenceEquals(_ctrl, parent.GetChildAtPoint(parent.PointToClient(pos))))
                {
                    var wParam = m.WParam.ToInt32();
                    Func<int, MouseButtons, MouseButtons> getButton =
                        (flag, button) => ((wParam & flag) == flag) ? button : MouseButtons.None;

                    var buttons = getButton(wParam & 0x0001, MouseButtons.Left)
                                | getButton(wParam & 0x0010, MouseButtons.Middle)
                                | getButton(wParam & 0x0002, MouseButtons.Right)
                                | getButton(wParam & 0x0020, MouseButtons.XButton1)
                                | getButton(wParam & 0x0040, MouseButtons.XButton2)
                                ; // Not matching for these /*MK_SHIFT=0x0004;MK_CONTROL=0x0008*/

                    var delta = wParam >> 16;
                    var e = new MouseEventArgs(buttons, 0, clientPos.X, clientPos.Y, delta);
                    _onMouseWheel(e);

                    return true;
                }
            }
            return false;
        }
    }
}

And then this can used from individual controls like

class MyControl
    : Control
{
    public MyControl()
    {
        ...
        MouseWheelHandler.Add(this, MyOnMouseWheel);
    }

    void MyOnMouseWheel(MouseEventArgs e)
    {
        ...
    }
}

Answer 4

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

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 works great, thx Hans Passant