The first time a user tries to expand an item to see its children, PowerBuilder triggers the ItemPopulate event if and only if the value of the item’s Children property is TRUE. In the ItemPopulate event, you can add child items for the item being expanded.
Parent item’s Children property
If the ItemPopulate event does not occur when you expect,
make sure the Children property for the expanding item is TRUE.
It should be set to TRUE for any item that will
have children.
Inserting items not restricted to the ItemPopulate event The ItemPopulate event helps you design an efficient program. It will not populate an item that the user never looks at. However, you do not have to wait until the user wants to view an item’s children. You can add children in any script, just as you added items at the root level.
For example, you might fully populate a small TreeView when its window opens and use the ExpandAll function to display its items fully expanded.
Has an item been populated? You can check an item’s ExpandedOnce property to find out if the user has looked at the item’s children. If the user is currently looking at an item’s children, the Expanded property is also TRUE.
Example This TreeView lists composers and their music organized into categories. The script for its ItemPopulate event checks whether the item being expanded is at level 1 (a composer) or level 2 (a category). Level 3 items are not expandable.
For a level 1 item, the script adds three standard categories. For a level 2 item, it adds pieces of music to the category being expanded, in this pattern:
Mozart Orchestral Symphony No. 33 Overture to the Magic Flute Chamber Quintet in Eb for Horn and Strings Eine Kleine Nachtmusik Vocal Don Giovanni Idomeneo
This is the script for ItemPopulate:
TreeViewItem tvi_current, tvi_child, tvi_root long hdl_root Integer ct string categ[] // The current item is the parent for the new itemsThis.GetItem(handle, tvi_current) IF tvi_current.Level = 1 THEN // Populate level 2 with some standard categories categ[1] = "Orchestral" categ[2] = "Chamber" categ[3] = "Vocal" tvi_child.StatePictureIndex = 0 tvi_child.PictureIndex = 3 tvi_child.SelectedPictureIndex = 4 tvi_child.OverlayPictureIndex = 0 tvi_child.Children = TRUE FOR ct = 1 to UpperBound(categ) tvi_child.Label = categ[ct] This.InsertItemLast(handle, tvi_child) NEXT END IF // Populate level 3 with music titles IF tvi_current.Level = 2 THEN // Get parent of current item - it's the root of // this branch and is part of the key for choosing // the children hdl_root = This.FindItem(ParentTreeItem!, handle) This.GetItem(hdl_root, tvi_root) FOR ct = 1 to 4 // This statement constructs a label - // it is more realistic to look up data in a // table or database or accept user input This.InsertItemLast(handle, & tvi_root.Label + " Music " & + tvi_current.Label + String(ct), 3) NEXT END IF
