Synchronizing Multiline Textbox Positions in C#

Question

I have a C# application wherein there are two multiline textboxes side-by-side, each in one side of a split-container. I would like to synchronize their vertical scroll, so that when the user scrolls up or down one of the textboxes, the other textbox scrolls respectively in the same direction. Is there a way to do this? Thanks.

ADDITIONAL INFORMATION - 7/26/10

I found some interesting APIs on the MSDN website:

TextBox.GetFirstVisibleLineIndex Method
TextBox.GetLastVisibleLineIndex Method
TextBox.ScrollToLine Method

The documentation there looks promising, but my compiler (Microsoft Visual C# 2008 Express Edition) complains when I try to use it, even after adding the PresenationFramework as a Reference and inserting using System.Windows.Controls; at the top of the file:

Error 1 'System.Windows.Forms.TextBox' does not contain a definition for 'GetFirstVisibleLineIndex' and no extension method 'GetFirstVisibleLineIndex' accepting a first argument of type 'System.Windows.Forms.TextBox' could be found (are you missing a using directive or an assembly reference?)

ADDITIONAL INFORMATION - 7/27/10

I'm working on implementing Jay's suggestion of implementing a new control, but I'm having trouble tying the eventhandler into the control. Here's is what I have so far:

public partial class MyFormApplication : Form
{
  public MyFormApplication() // MyFormApplication constructor
  {
     this.InitializeComponent();

     this.textBox1.Dispose(); // Replacing with textBoxSync1
     this.textBox2.Dispose(); // Replacing with textBoxSync2

     // Draw textBoxSync1
     this.textBoxSync1.AcceptsReturn = true;
     this.textBoxSync1.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom)
        | System.Windows.Forms.AnchorStyles.Left)
        | System.Windows.Forms.AnchorStyles.Right)));
     this.textBoxSync1.BackColor = System.Drawing.SystemColors.Control;
     this.textBoxSync1.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle;
     this.textBoxSync1.Font = new System.Drawing.Font("Courier New", 8.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
     this.textBoxSync1.Location = new System.Drawing.Point(0, 19);
     this.textBoxSync1.Multiline = true;
     this.textBoxSync1.Name = "textBoxSync1";
     this.textBoxSync1.ReadOnly = true;
     this.textBoxSync1.ScrollBars = System.Windows.Forms.ScrollBars.Both;
     this.textBoxSync1.Size = new System.Drawing.Size(338, 231);
     this.textBoxSync1.TabIndex = 0;
     this.textBoxSync1.TabStop = false;
     this.textBoxSync1.WordWrap = false;
     this.splitContainer1.Panel1.Controls.Remove(this.textBox1);
     this.splitContainer1.Panel1.Controls.Add(this.textBoxSync1);

     // Draw textBoxSync2
     this.textBoxSync2.AcceptsReturn = true;
     this.textBoxSync2.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom)
        | System.Windows.Forms.AnchorStyles.Left)
        | System.Windows.Forms.AnchorStyles.Right)));
     this.textBoxSync2.BackColor = System.Drawing.SystemColors.Control;
     this.textBoxSync2.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle;
     this.textBoxSync2.Font = new System.Drawing.Font("Courier New", 8.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
     this.textBoxSync2.Location = new System.Drawing.Point(0, 19);
     this.textBoxSync2.Multiline = true;
     this.textBoxSync2.Name = "textBoxSync2";
     this.textBoxSync2.ReadOnly = true;
     this.textBoxSync2.ScrollBars = System.Windows.Forms.ScrollBars.Both;
     this.textBoxSync2.Size = new System.Drawing.Size(113, 231);
     this.textBoxSync2.TabIndex = 30;
     this.textBoxSync2.TabStop = false;
     this.textBoxSync2.WordWrap = false;
     this.splitContainer1.Panel2.Controls.Remove(this.textBox2);
     this.splitContainer1.Panel2.Controls.Add(this.textBoxSync2);

     /* Goes on to perform other initializations... */

  }

  private void textBoxSync1_VerticalScroll(Message msg)
  {
     msg.HWnd = this.textBoxSync2.Handle;
     this.textBoxSync2.PubWndProc(ref msg);
  }

  private void textBoxSync2_VerticalScroll(Message msg)
  {
     msg.HWnd = this.textBoxSync1.Handle;
     this.textBoxSync1.PubWndProc(ref msg);
  }
}

public class TextBoxSynchronizedScroll : System.Windows.Forms.TextBox
{
  public event vScrollEventHandler VerticalScroll;
  public delegate void vScrollEventHandler(System.Windows.Forms.Message message);

  public const int WM_VSCROLL = 0x115;

  protected override void WndProc(ref System.Windows.Forms.Message msg)
  {
     if (msg.Msg == WM_VSCROLL)
     {
        if (VerticalScroll != null)
        {
           VerticalScroll(msg);
        }
     }

     base.WndProc(ref msg);
  }

  public void PubWndProc(ref System.Windows.Forms.Message msg)
  {
     base.WndProc(ref msg);
  }
}

I should think that something like...

this.textBoxSync1.VerticalScroll += new System.EventHandler(this.textBoxSync1_VerticalScroll);

...would be needed to hook the vertical scroll event into the control, but as you can probably see, this does not work. Any suggestions would be appreciated. Thanks.

Answer 1

Have you tried intercepting all the scroll-related Windows messages coming to one textbox and just re-sending them to the other textbox?

Answer 2

I subclassed a RichTextBox and listened for the WM_VSCROLL message to do what you're trying to do. Perhaps you can do that instead of using a TextBox.

RESPONSE TO YOUR EDIT:

Note: I'm assuming you made a minor error in the copy and paste in your Application form and that textBoxSyncBusTraffic == textBoxSync1

The problem is in your declaration of your control's VerticalScroll event, in this line:

this.textBoxSyncBusTraffic.VerticalScroll += new System.EventHandler(this.textBoxSyncBusTraffic_VerticalScroll); 

1. Your custom controls need to subscribe to your controls' TextBoxSynchronizedScroll.vScrollEventHandler events (not to System.EventHandler).
2. The method referenced in your event handler doesn't exist (at least not in the code you posted).

So change this:

this.textBoxSyncBusTraffic.VerticalScroll += new System.EventHandler(this.textBoxSyncBusTraffic_VerticalScroll); 

To this:

this.textBoxSync1.VerticalScroll += new TextBoxSynchronizedScroll.vScrollEventHandler(textBoxSync1_VerticalScroll);

This uses the correct event handler and references the method you need and already have.

Also, make sure that the declaration for textBoxSync2's VerticalScroll event looks like this:

this.textBoxSync2.VerticalScroll += new TextBoxSynchronizedScroll.vScrollEventHandler(textBoxSync2_VerticalScroll);

Incidentally, there are a couple techniques you can use to make it easier to declare events:

The first is to use the form designer. If you open the Events window in the Properties window of an instance of your extended control in the forms designer, you'll see an event called VerticalScroll. Double click this item to have Visual Studio declare the event and create a method to call when the event fires.

There's also a shortcut you can use when you set up your event in code. You'll find that after you type the following code:

youtextBoxSync1.VerticalScroll +=

You'll be prompted to press Tab to finish the declaration. If you do this Visual Studio will create a method with the correct signature.

Answer 3

Based of the existing code I came up with the following. Seems to work for me.

class TextBoxSynchronizedScroll : TextBox
{
    public const int WM_VSCROLL = 0x115;

    List<TextBoxSynchronizedScroll> peers = new List<TextBoxSynchronizedScroll>();

    public void AddPeer(TextBoxSynchronizedScroll peer)
    {
        this.peers.Add(peer);
    }

    private void DirectWndProc(ref Message m)
    {
        base.WndProc(ref m);
    }

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == WM_VSCROLL)
        {
            foreach (var peer in this.peers)
            {
                var peerMessage = Message.Create(peer.Handle, m.Msg, m.WParam, m.LParam);
                peer.DirectWndProc(ref peerMessage);
            }
        }

        base.WndProc(ref m);
    }
}

http://gist.github.com/593809