Using DataWindow information to populate a TreeView – PB Docs 70

Using DataWindow information to populate a TreeView

A useful
implementation of the TreeView control is to populate it with information
that you retrieve from a DataWindow. To do this your application will:

  • Declare and instantiate
    a DataStore and assign a DataWindow object
  • Retrieve information as needed
  • Use the retrieved information to populate the TreeView
  • Destroy the DataStore instance when you are finished

Because a TreeView can display different types of information
at different levels, you will probably define additional DataWindows,
one for each level. Those DataWindows usually refer to different
but related tables. When an item is expanded, the item becomes a
retrieval argument for getting child items.

Populating the first level

This example populates a TreeView with a list of composers.
The second level of the TreeView displays music by each composer. In the database
there are two tables: composer names and music titles (with composer
name as a foreign key).

This example declares two DataStore instance variables for
the window containing the TreeView control:

This example uses the TreeView control’s Constructor
event to:

  • Instantiate the DataStore
  • Associate it with a DataWindow and retrieve information
  • Use the retrieved data to populate the root level
    of the TreeView

Populating the second level

When the user expands a root level item, the ItemPopulate
event occurs. This script for the event:

  • Instantiates a second
    DataStore. Its DataWindow uses the composer name as a retrieval
    argument for the music titles table.
  • Inserts music titles as child items for the selected
    composer. The handle argument of ItemPopulate will be the parent
    of the new items.

Destroying DataStore instances

When the window containing the TreeView control closes, this
example destroys the DataStore instances:

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