Be careful of TreeView.Nodes.Clear

As you may have surmised from my last post, we were dealing with some performance issues in a treeview when it was repopulating nodes. This is an older tip but it's certainly something to consider if you are using TreeViews. I got the tip here and it's a good one.

When the Nodes.Clear method is called, it refreshes the treeview for each node it removes.

If your treeview is small, you won't really notice it but if you have a lot of entries on it, it's really noticeable.

Here's a quick test to try
1. Build a form with a treeview on it.
2. Add 200 nodes to it:
WITH THISFORM.TreeView
FOR lni = 1 TO 200
.Nodes.Add(,"_"+LTRIM(STR(lni)),"Item "+LTRIM(STR(lni)))
ENDFOR
ENDWITH

3. Just issue a _SCREEN.Activeform.treeview.nodes.clear() in the Command window and see how long it takes for control to come back. It can be a while. (my test showed 14 seconds - YIKES!!!)

Instead, remove each node individually:

FOR lni = 1 TO THISFORM.Treeview.nodes.Count to 1 STEP -1
THISFORM.TreeView.Nodes.Remove(lni)
ENDFOR

The result? The list goes away in under a second.

Sounds like if you have a tree view in your application, you should subclass it and create a clearNodes method to get rid of it.

The other approach?

THISFORM.treeview.visible = false
THISFORM.treeview.nodes.clear
THISFORM.treeview.visible = true

Another instant result.

Comments

Sergey Berezniker said…
Another way to speed it up

DECLARE INTEGER LockWindowUpdate IN WIN32API INTEGER hWnd
=LockWindowUpdate(Thisform.TreeView.hWnd)
Thisform.TreeView.OBJECT.Nodes.Clear
=LockWindowUpdate(0)

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