How to make a wide virtual Tree-View Control with only two levels fast?

Question

I basically want to have the same virtual performance I can get with a List-View control. With a List-View control you can set an ItemCount and in the LVN_GETDISPINFO notification you then fill in the information for the items once they are scrolled visible.

Now, the virtual functionality the Tree-View provides is good for very deep trees, so you would only add items once a node expands (via TVN_ITEMEXPANDING), and TVN_GETDISPINFO can be used for filling in item information once the item is scrolled visible. But what to do if you have an "always expanded" two-level tree (just for design matters) where TVN_ITEMEXPANDING wouldn't be of any use and only want to add the items once they would be visible. The problem is, there's no such thing as SetItemCount() or similar to already resize the tree.

In my case, the filling of item information (text, image, selected image) isn't the expensive part, but the inserting of items (all at one level) is.

One option would be to only insert the items which would be visible plus one invisible one, once the invisible one gets visible (detected in TVN_GETDISPINFO), I'd insert a few more and so on. But then the scrollbar would always get smaller the more I scroll down, I think that's weird.

Are there any other ideas to achieve what I want except from drawing my own control?

The whole tree would just look like this, pretty much a list, it's just that I like the tree-look.

RootNode
|
|--Item 1
|--Item 2
|--Item 3
|--Item 4
|--Item 5
|--Item 6
|--Item 7
...
|__Item 1000

Answer 1

As stated in many other posts, the really expensive part about the Tree-View control is using InsertItem and DeleteItem. A quick way to improve performance for those operations is making use of SetRedraw. Not only does it hide the flickering but does really speed things up, since the drawing seems to be expensive - even though TVN_GETDISPINFO is used.

Also, it's faster to rename existing items and change their data instead of deleting and adding new ones. So when I have a big list and know that the next update will contain about the same amount +/- a couple ones, I go iterate through the items, rename them, change their lparams and sync (i.e. remove/add) the remaining ones in accordance to the new data. Depending on the size of the list, making those extra calculations can have a huge performance improvement.

Answer 2

The Win32 TreeView control does not support the kind of virtual mode you are looking for. So you will need a custom control.