Tree Control Item Selection
When the selection changes from one item to another, a tree control () sends and notification messages. Both notifications include a value that specifies whether the change is the result of a mouse click or a keystroke. The notifications also include information about the item that is gaining the selection and the item that is losing the selection. You can use this information to set item attributes that depend on the selection state of the item. Returning TRUE in response to TVN_SELCHANGING prevents the selection from changing; returning FALSE allows the change.
An application can change the selection by calling the member function.