Make two ListBoxes scroll together - listbox

Question

I wish to make two ListBoxes scroll together.
I have two ListBoxes of the same height with the same number of items, etc. I want to set it up such that if the user scrolls up/down in one list box the scrollbar for the other ListBox scrolls up/down as well.
But I can not seem to find a way to either detect the scroll bar position value or to detect when it has changed value.

Answer 1

Here is another way to sync the two ListBoxes:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace SyncTwoListBox
{
public partial class Form1 : Form
{
private SyncListBoxes _SyncListBoxes = null;
public Form1()
{
InitializeComponent();
this.Load += Form1_Load;
//add options
for (int i = 0; i < 40; i++)
{
listBox1.Items.Add("Item " + i);
listBox2.Items.Add("Item " + i);
}
}
private void Form1_Load(object sender, EventArgs e)
{
this._SyncListBoxes = new SyncListBoxes(this.listBox1, this.listBox2);
}
}
public class SyncListBoxes
{
private ListBox _LB1 = null;
private ListBox _LB2 = null;
private ListBoxScroll _ListBoxScroll1 = null;
private ListBoxScroll _ListBoxScroll2 = null;
public SyncListBoxes(ListBox LB1, ListBox LB2)
{
if (LB1 != null && LB1.IsHandleCreated && LB2 != null && LB2.IsHandleCreated &&
LB1.Items.Count == LB2.Items.Count && LB1.Height == LB2.Height)
{
this._LB1 = LB1;
this._ListBoxScroll1 = new ListBoxScroll(LB1);
this._ListBoxScroll1.Scroll += _ListBoxScroll1_VerticalScroll;
this._LB2 = LB2;
this._ListBoxScroll2 = new ListBoxScroll(LB2);
this._ListBoxScroll2.Scroll += _ListBoxScroll2_VerticalScroll;
this._LB1.SelectedIndexChanged += _LB1_SelectedIndexChanged;
this._LB2.SelectedIndexChanged += _LB2_SelectedIndexChanged;
}
}
private void _LB1_SelectedIndexChanged(object sender, EventArgs e)
{
if (this._LB2.TopIndex != this._LB1.TopIndex)
{
this._LB2.TopIndex = this._LB1.TopIndex;
}
if (this._LB2.SelectedIndex != this._LB1.SelectedIndex)
{
this._LB2.SelectedIndex = this._LB1.SelectedIndex;
}
}
private void _LB2_SelectedIndexChanged(object sender, EventArgs e)
{
if (this._LB1.TopIndex != this._LB2.TopIndex)
{
this._LB1.TopIndex = this._LB2.TopIndex;
}
if (this._LB1.SelectedIndex != this._LB2.SelectedIndex)
{
this._LB1.SelectedIndex = this._LB2.SelectedIndex;
}
}
private void _ListBoxScroll1_VerticalScroll(ListBox LB)
{
if (this._LB2.TopIndex != this._LB1.TopIndex)
{
this._LB2.TopIndex = this._LB1.TopIndex;
}
}
private void _ListBoxScroll2_VerticalScroll(ListBox LB)
{
if (this._LB1.TopIndex != this._LB2.TopIndex)
{
this._LB1.TopIndex = this._LB2.TopIndex;
}
}
private class ListBoxScroll : NativeWindow
{
private ListBox _LB = null;
private const int WM_VSCROLL = 0x115;
private const int WM_MOUSEWHEEL = 0x20a;
public event dlgListBoxScroll Scroll;
public delegate void dlgListBoxScroll(ListBox LB);
public ListBoxScroll(ListBox LB)
{
this._LB = LB;
this.AssignHandle(LB.Handle);
}
protected override void WndProc(ref Message m)
{
base.WndProc(ref m);
switch (m.Msg)
{
case WM_VSCROLL:
case WM_MOUSEWHEEL:
if (this.Scroll != null)
{
this.Scroll(_LB);
}
break;
}
}
}
}
}
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