Maintain scroll position of treeview

Question

How can I maintain the scroll position of a treeview control in .NET application? For example, I have a treeview control and go through a process of adding various nodes to it tacking them on to the bottom. During this process, I can scroll through the treeview and view different nodes. The problem is when the process completes, the treeview scrolls to the very bottom.

It appears that calling treenode.Expand() is what is throwing me off track here. When a parent node is expanded, it gets the focus.

Is there a way around this? If I'm looking at a specific node while the process is running, I don't want it to jump around on me when the process is done.

Answer 1

I think I figured it out:

1. Get the node at the top of the treeview.
2. Expand the parent node.
3. Make the node that was previously at the top visible.

If treeNodeParent.IsExpanded = False Then
    Dim currentNode As TreeNode = TreeViewHosts.GetNodeAt(0, 0)
    treeNodeParent.Expand()
    currentNode.EnsureVisible()
End If

Is the a better way to do this?

Answer 2

I'm not a VB guy but in C# I do it this way:

Some Win32 native functions:

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

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

private const int SB_HORZ = 0x0;
private const int SB_VERT = 0x1;

A method which returns a point for the current scroll position:

private Point GetTreeViewScrollPos(TreeView treeView)
{
    return new Point(
        GetScrollPos((int)treeView.Handle, SB_HORZ), 
        GetScrollPos((int)treeView.Handle, SB_VERT));
}

A method to set the scroll position:

private void SetTreeViewScrollPos(TreeView treeView, Point scrollPosition)
{
    SetScrollPos((IntPtr)treeView.Handle, SB_HORZ, scrollPosition.X, true);
    SetScrollPos((IntPtr)treeView.Handle, SB_VERT, scrollPosition.Y, true); 
}

Then when you update your tree, do the following:

Point ScrollPos = GetTreeViewScrollPos(treeMain);
// write your update code here
SetTreeViewScrollPos(treeMain, ScrollPos);

Answer 3

I found it's best to wrap the "SetTreeViewScrollPosition(point)" with a Begin and End Update...

    private void treeViewXml1_Scroll(object sender, ScrollEventArgs e)
    {
        Point point = treeViewXml1.GetTreeViewScrollPosition();

        treeViewXml2.BeginUpdate();
        treeViewXml2.SetTreeViewScrollPosition(point);
        treeViewXml2.EndUpdate();
    }

    private void treeViewXml2_Scroll(object sender, ScrollEventArgs e)
    {
        Point point = treeViewXml2.GetTreeViewScrollPosition();

        treeViewXml1.BeginUpdate();
        treeViewXml1.SetTreeViewScrollPosition(point);
        treeViewXml1.EndUpdate();
    }