C# ScrollableControl does not receive all scroll events

Question

I am experiencing a problem with the ScrollableControl (a Panel to be more precise). When scrolling with the mouse pointer directly on the scroll bar, the Scroll event is fired properly.

But when scrolling with the mouse wheel, the Panel scrolls properly but the Scroll event is not fired.

Also when an out of bounds control inside the Panel receives the focus, the Panel properly scrolls to bring the control in view, but once again, in that case, the Scroll event is not fired.

Did any of you experienced the same thing ? Did you find a solution ?

Thanks !

Answer 1

Update: I have now tested - this does NOT work!

I haven't tested it yet, but according to this: http://www.codeproject.com/Articles/7452/ScrollableControl-with-Scroll-Events one option is to extend the functionality of the ScrollableControl

The code is as follows:

using System;
using System.ComponentModel;
using System.Windows.Forms;
using System.Diagnostics;

namespace Foretel.SelectAGrid
{
    /// <summary>
    /// Adds the missing scroll events to the scrollable control!
    /// Written by Martin Randall - Thursday 17th June, 2004
    /// </summary>
    public class ScrollableControlWithScrollEvents : ScrollableControl
    {
        private const int WM_HSCROLL = 0x114;
        private const int WM_VSCROLL = 0x115;

        /// <summary>
        /// Horizontal scroll position has changed event
        /// </summary>
        public event ScrollEventHandler HorzScrollValueChanged;

        /// <summary>
        /// Vertical scroll position has changed event
        /// </summary>
        public event ScrollEventHandler VertScrollValueChanged;

        /// <summary>
        /// Intercept scroll messages to send notifications
        /// </summary>
        /// <param name="m">Message parameters</param>
        protected override void WndProc(ref Message m)
        {
            // Let the control process the message
            base.WndProc (ref m);

            // Was this a horizontal scroll message?
            if ( m.Msg == WM_HSCROLL ) 
            {
                if ( HorzScrollValueChanged != null ) 
                {
                    uint wParam = (uint)m.WParam.ToInt32();
                    HorzScrollValueChanged( this, 
                        new ScrollEventArgs( 
                            GetEventType( wParam & 0xffff), (int)(wParam >> 16) ) );
                }
            } 
            // or a vertical scroll message?
            else if ( m.Msg == WM_VSCROLL )
            {
                if ( VertScrollValueChanged != null )
                {
                    uint wParam = (uint)m.WParam.ToInt32();
                    VertScrollValueChanged( this, 
                        new ScrollEventArgs( 
                        GetEventType( wParam & 0xffff), (int)(wParam >> 16) ) );
                }
            }
        }

        // Based on SB_* constants
        private static ScrollEventType [] _events =
            new ScrollEventType[] {
                                      ScrollEventType.SmallDecrement,
                                      ScrollEventType.SmallIncrement,
                                      ScrollEventType.LargeDecrement,
                                      ScrollEventType.LargeIncrement,
                                      ScrollEventType.ThumbPosition,
                                      ScrollEventType.ThumbTrack,
                                      ScrollEventType.First,
                                      ScrollEventType.Last,
                                      ScrollEventType.EndScroll
                                  };
        /// <summary>
        /// Decode the type of scroll message
        /// </summary>
        /// <param name="wParam">Lower word of scroll notification</param>
        /// <returns></returns>
        private ScrollEventType GetEventType( uint wParam )
        {
            if ( wParam < _events.Length )
                return _events[wParam];
            else
                return ScrollEventType.EndScroll;
        }
    }
}