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Navigation

Given a tree or an item in a tree, there are a limited number of possible ways to go from there. You can get the topmost item, the next sibling, the previous sibling, the first child or the parent.

Delayed Population

Let’s take the situation where we want to wait until the user clicks on an item’s ‘+’ sign to populate the children of the selected item. The parent to the control is set up to receive TVN_ITEMEXPANDING notification messages. Let’s further stipulate that the population exercise only happens once. Once populated, don’t do it again.

 OK, first thing – what triggers the tree to put a ‘+’ on an item? It will only happen if the item has a child. Since we don’t actually go out and look for an item’s children until it is expanded, we have ourselves a problem. If the item has no children then it doesn’t have a ‘+’. The work around is to append a blank item to each item when it is added. Then, at expansion time, we look at the first child of the item. If the child is blank then this item has never been expanded before and needs to be populated. Delete the blank child item and populate the item’s children.

Image List

One of the really nice things about the tree control is the ability to associate a small bitmap with each item in the tree. The tree control has a single bitmap which is subdivided into a series of bitmaps. Each item in the control gets the zero relative index of two separate sub bitmaps, one for when the item is selected and one for, oddly enough, when the item isn’t selected. Fancy that.

The image list itself is encapsulated within a CImageList.

Getting Check State

If the tree control has the checkbox attribute then you can ask the tree control for the check state.