ListView onScroll event

Question

Hi, I’m programming one easy C# application, and i need onScroll event on Listview. So i created class ListviewEx witch inherits original ListView. I found how to detect scroll message from WinAPI and i modified WndProc method. Now i have this WndProc:

protected override void WndProc(ref Message m) 
{ 
    base.WndProc(ref m); 

    if (m.Msg == WM_VSCROLL) 
    { 
        onScroll(this, new EventArgs()); 
    } 
}

But problem is, that I dont know how to detect information about scrolling. This data should be in WParam, but in C# is no LOWORD macro like in C++ and i need switch to detect parameters like SB_ BOTTOM, SB_ ENDSCROLL, SB_PAGEUP etc.

Is there any way how to replace LOWORD macro in C# ?

Or other way how to detect necessary parameters about scrolling?

Answer 1

You can define WParam constants as followed:

private const int WM_HSCROLL = 0x114;
private const int WM_VSCROLL = 0x115;

private const int SB_HORZ = 0;
private const int SB_VERT = 1;

private const int SB_LINELEFT = 0;
private const int SB_LINERIGHT = 1;
private const int SB_PAGELEFT = 2;
private const int SB_PAGERIGHT = 3;
private const int SB_THUMBPOSITION = 4;
private const int SB_THUMBTRACK = 5;
private const int SB_LEFT = 6;
private const int SB_RIGHT = 7;
private const int SB_ENDSCROLL = 8;

private const int SIF_TRACKPOS = 0x10;
private const int SIF_RANGE = 0x1;
private const int SIF_POS = 0x4;
private const int SIF_PAGE = 0x2;
private const int SIF_ALL = SIF_RANGE | SIF_PAGE | SIF_POS | SIF_TRACKPOS;

The actual code to inspect the WParam would be something like this:

if (m.Msg == WM_VSCROLL)
{

        ScrollInfoStruct si = new ScrollInfoStruct();
        si.fMask = SIF_ALL;
        si.cbSize = (uint)Marshal.SizeOf(si);
        GetScrollInfo(msg.HWnd, SB_VERT, ref si);
        if (msg.WParam.ToInt32() == SB_ENDSCROLL)
        {
            ScrollEventArgs sargs = new ScrollEventArgs(ScrollEventType.EndScroll, si.nPos);
            onScroll(this, sargs);
        }
}

pinvoke.net is a great site to get the constant values used in windows32 API without having to inspect header files yourself.

See this example

Answer 2

Martijn answer will work but will not catch all scrolling. The *WM_VSCROLL* message is only sent when the user manipulates the scroll bar directly. If the user scrolls using a mouse wheel, or uses the UpArrow/DownArrow/PageUp/PageDown keys, then the *WM_VSCROLL* will not be sent.

You can catch scrolling that is caused by the scroll bar and by the mouse wheel by listening for the *LVN_BEGINSCROLL* notification message.

Catching scrolling that occurs when using keys is harder. No message that is sent to the control when it scrolls in response to a PageUp key, for example. The best that can be done in that case is to listen for KeyPress events, and then check for changes to the scroll bar positions before and after the event.

This could, of course, be complete overkill for your purposes. The *WM_VSCROLL* message may be completely sufficient for what you want. But if you want to catch all possible scrolling, have a look at the code in ObjectListView which already has a Scroll event that catches all these possibilities.

Answer 3

Thanks for your answers. It really helped me :) Now I have what I wanted...

Here is code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using Microsoft.Win32;
using System.Reflection;

namespace ControlsEx
{
    public class ListViewEx : ListView
    {
        // Windows messages
        private const int WM_PAINT      = 0x000F;
        private const int WM_HSCROLL    = 0x0114;
        private const int WM_VSCROLL    = 0x0115;
        private const int WM_MOUSEWHEEL = 0x020A;
        private const int WM_KEYDOWN    = 0x0100;
        private const int WM_LBUTTONUP  = 0x0202;                 

        // ScrollBar types
        private const int SB_HORZ = 0;
        private const int SB_VERT = 1;

        // ScrollBar interfaces
        private const int SIF_TRACKPOS  = 0x10;
        private const int SIF_RANGE     = 0x01;
        private const int SIF_POS       = 0x04;
        private const int SIF_PAGE      = 0x02;
        private const int SIF_ALL       = SIF_RANGE | SIF_PAGE | SIF_POS | SIF_TRACKPOS;

        // ListView messages
        private const uint LVM_SCROLL       = 0x1014;
        private const int  LVM_FIRST        = 0x1000;                   
        private const int  LVM_SETGROUPINFO = (LVM_FIRST + 147);  

        public enum ScrollBarCommands : int
        {
            SB_LINEUP = 0,
            SB_LINELEFT = 0,
            SB_LINEDOWN = 1,
            SB_LINERIGHT = 1,
            SB_PAGEUP = 2,
            SB_PAGELEFT = 2,
            SB_PAGEDOWN = 3,
            SB_PAGERIGHT = 3,
            SB_THUMBPOSITION = 4,
            SB_THUMBTRACK = 5,
            SB_TOP = 6,
            SB_LEFT = 6,
            SB_BOTTOM = 7,
            SB_RIGHT = 7,
            SB_ENDSCROLL = 8
        }

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);

            switch(m.Msg)
            {
                case WM_VSCROLL:
                    ScrollEventArgs sargs = new ScrollEventArgs(ScrollEventType.EndScroll, GetScrollPos(this.Handle, SB_VERT));
                    onScroll(this, sargs);
                    break;

                case WM_MOUSEWHEEL:
                    ScrollEventArgs sarg = new ScrollEventArgs(ScrollEventType.EndScroll, GetScrollPos(this.Handle, SB_VERT));
                    onScroll(this, sarg);
                    break;

                case WM_KEYDOWN:
                    switch (m.WParam.ToInt32())
                    {
                        case (int)Keys.Down:
                            onScroll(this, new ScrollEventArgs(ScrollEventType.SmallDecrement, GetScrollPos(this.Handle, SB_VERT)));
                            break;
                        case (int)Keys.Up:
                            onScroll(this, new ScrollEventArgs(ScrollEventType.SmallIncrement, GetScrollPos(this.Handle, SB_VERT)));
                            break;
                        case (int)Keys.PageDown:
                            onScroll(this, new ScrollEventArgs(ScrollEventType.SmallDecrement, GetScrollPos(this.Handle, SB_VERT)));
                            break;
                        case (int)Keys.PageUp:
                            onScroll(this, new ScrollEventArgs(ScrollEventType.SmallIncrement, GetScrollPos(this.Handle, SB_VERT)));
                            break;
                        case (int)Keys.Home:
                            onScroll(this, new ScrollEventArgs(ScrollEventType.First, GetScrollPos(this.Handle, SB_VERT)));
                            break;
                        case (int)Keys.End:
                            onScroll(this, new ScrollEventArgs(ScrollEventType.Last, GetScrollPos(this.Handle, SB_VERT)));
                            break;
                    }   
                    break;
            }

        }

        public int ScrollPosition 
        {
            get
            {
                return GetScrollPos(this.Handle, SB_VERT);
            }
            set
            {
                int prevPos;
                int scrollVal;

                if (ShowGroups == true)
                {
                    prevPos = GetScrollPos(this.Handle, SB_VERT);
                    scrollVal = -(prevPos - value);
                }
                else
                {
                  // TODO: Add setScrollPosition if ShowGroups == false
                }

                SendMessage(this.Handle, LVM_SCROLL, (IntPtr)0, (IntPtr)scrollVal);
            }
        }

        public event ScrollEventHandler onScroll;

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool GetScrollInfo(IntPtr hwnd, int fnBar, ref SCROLLINFO lpsi);

        [DllImport("user32.dll")]
        public static extern int SendMessage(
              int hWnd,      // handle to destination window
              uint Msg,       // message
              long wParam,  // first message parameter
              long lParam   // second message parameter
              );

        [DllImport("user32.dll")]
        static extern int SendMessage(IntPtr hWnd, int wMsg,
                                       int wParam, int lParam);

        [DllImport("user32.dll")]
        static extern int SendMessage(IntPtr hWnd, uint wMsg,
                                       IntPtr wParam, IntPtr lParam);

        [DllImport("user32.dll")]
        static extern int SetScrollPos(IntPtr hWnd, int nBar, int nPos, bool bRedraw);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static extern int GetScrollPos(IntPtr hWnd, int nBar);


        [StructLayout(LayoutKind.Sequential)]
        struct SCROLLINFO
        {
            public uint cbSize;
            public uint fMask;
            public int nMin;
            public int nMax;
            public uint nPage;
            public int nPos;
            public int nTrackPos;
        }
    }
}