Monday, May 16, 2011

Synchronized ListBox objects (or how to scroll 2 ListBox objects together)

Before couple of days I had a task where I must synchronize two ListBox objects. I have fount out, that ListBox object doesn't have any property which allow to accomplish this. After a few hours of googling I found code of class that inherited from ListBox class. Here is the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.ComponentModel;
using System.Runtime.InteropServices;
namespace SyncLists
{
    class SyncListBox : System.Windows.Forms.ListBox
    {
        [Category("Action")]

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

        public event ScrollEventHandler OnHorizontalScroll;
        public event ScrollEventHandler OnVerticalScroll;


        private const int SB_LINEUP = 0;
        private const int SB_LINELEFT = 0;
        private const int SB_LINEDOWN = 1;
        private const int SB_LINERIGHT = 1;
        private const int SB_PAGEUP = 2;
        private const int SB_PAGELEFT = 2;
        private const int SB_PAGEDOWN = 3;
        private const int SB_PAGERIGHT = 3;
        private const int SB_THUMBPOSITION = 4;
        private const int SB_THUMBTRACK = 5;
        private const int SB_PAGETOP = 6;
        private const int SB_LEFT = 6;
        private const int SB_PAGEBOTTOM = 7;
        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;

        [DllImport("user32.dll", SetLastError = true)]
        private static extern int GetScrollInfo(
        IntPtr hWnd, int n, ref ScrollInfoStruct lpScrollInfo);


        private struct ScrollInfoStruct
        {
            public int cbSize;
            public int fMask;
            public int nMin;
            public int nMax;
            public int nPage;
            public int nPos;
            public int nTrackPos;
        }

        protected override void WndProc(ref System.Windows.Forms.Message msg)
        {
            if (msg.Msg == WM_HSCROLL)
            {
                if (OnHorizontalScroll != null)
                {
                    ScrollInfoStruct si = new ScrollInfoStruct();
                    si.fMask = SIF_ALL;
                    si.cbSize = Marshal.SizeOf(si);
                    GetScrollInfo(msg.HWnd, 0, ref si);

                    if (msg.WParam.ToInt32() == SB_ENDSCROLL)
                    {
                        ScrollEventArgs sargs = new ScrollEventArgs(
                        ScrollEventType.EndScroll,
                        si.nPos);
                        OnHorizontalScroll(this, sargs);
                    }
                }
            }
            if (msg.Msg == WM_VSCROLL)
            {
                if (OnVerticalScroll != null)
                {
                    ScrollInfoStruct si = new ScrollInfoStruct();
                    si.fMask = SIF_ALL;
                    si.cbSize = Marshal.SizeOf(si);
                    GetScrollInfo(msg.HWnd, 0, ref si);

                    if (msg.WParam.ToInt32() == SB_ENDSCROLL)
                    {
                        ScrollEventArgs sargs = new ScrollEventArgs(
                        ScrollEventType.EndScroll,
                        si.nPos);
                        OnVerticalScroll(this, sargs);
                    }
                }
            }
            base.WndProc(ref msg);
        }


        private void InitializeComponent()
        {
            this.SuspendLayout();
            // 
            // scrolled
            // 
            this.Size = new System.Drawing.Size(120, 95);
            this.ResumeLayout(false);
        }
    }
}

add two SyncListBox objects on the form and add following code:

private void syncListView2_OnVerticalScroll(object sender, ScrollEventArgs e)
{
    syncListView1.TopIndex = syncListView2.TopIndex;
}

private void syncListView1_OnVerticalScroll(object sender, ScrollEventArgs e)
{
    syncListView2.TopIndex = syncListView1.TopIndex;
}

3 comments:

  1. This is a nice article..
    Its very easy to understand ..
    And this article is using to learn something about it..
    asp.net, c#, javascript
    Thanks a lot..!

    ReplyDelete
  2. Robert,
    your code is too simple, since I am a new bee, I couldn't able to make it work with my project :(.
    Can you please make a downloadable project?

    ReplyDelete