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
  PowerBuilder

  //Constructor event for tv_1

  1	//Constructor event for tv_1

  
  
  PowerBuilder

  treeviewitem tvi1, tvi2

  1	treeviewitem tvi1, tvi2

  
  
  PowerBuilder

  long ll_lev1, ll_lev2, ll_rowcount, ll_row

  1	long ll_lev1, ll_lev2, ll_rowcount, ll_row

  
  
  1

  
  
  PowerBuilder

  //Create instance variable datastore

  1	//Create instance variable datastore

  
  
  PowerBuilder

  ids_data = CREATE datastore

  1	ids_data = CREATE datastore

  
  
  PowerBuilder

  ids_data.DataObject = "d_composers"

  1	ids_data.DataObject = "d_composers"

  
  
  PowerBuilder

  ids_data.SetTransObject(SQLCA)

  1	ids_data.SetTransObject(SQLCA)

  
  
  PowerBuilder

  ll_rowcount = ids_data.Retrieve()

  1	ll_rowcount = ids_data.Retrieve()

  
  
  1

  
  
  PowerBuilder

  //Create the first level of the TreeView

  1	//Create the first level of the TreeView

  
  
  PowerBuilder

  tvi1.PictureIndex = 1

  1	tvi1.PictureIndex = 1

  
  
  PowerBuilder

  tvi1.Children = TRUE

  1	tvi1.Children = TRUE

  
  
  PowerBuilder

  //Populate the TreeView with

  1	//Populate the TreeView with

  
  
  PowerBuilder

  //data retrieved from the datastore

  1	//data retrieved from the datastore

  
  
  PowerBuilder

  FOR ll_row = 1 to ll_rowcount

  1	FOR ll_row = 1 to ll_rowcount

  
  
  PowerBuilder

  tvi1.Label = ids_data.GetItemString(ll_row, &

  1	tvi1.Label = ids_data.GetItemString(ll_row, &

  
  
  PowerBuilder

  'name')

  1

  'name')

  
  
  PowerBuilder

  This.InsertItemLast(0, tvi1)

  1	This.InsertItemLast(0, tvi1)

  
  
  PowerBuilder

  NEXT

  1

  NEXT

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.
  PowerBuilder

  //ItemPopulate event for tv_1

  1	//ItemPopulate event for tv_1

  
  
  PowerBuilder

  TreeViewItem tvi1, tvi2

  1	TreeViewItem tvi1, tvi2

  
  
  PowerBuilder

  long ll_row, ll_rowcount

  1	long ll_row, ll_rowcount

  
  
  1

  
  
  PowerBuilder

  //Create instance variable datastore

  1	//Create instance variable datastore

  
  
  PowerBuilder

  ids_info = CREATE datastore

  1	ids_info = CREATE datastore

  
  
  PowerBuilder

  ids_info.DataObject = "d_music"

  1	ids_info.DataObject = "d_music"

  
  
  PowerBuilder

  ids_info.SetTransObject(SQLCA)

  1	ids_info.SetTransObject(SQLCA)

  
  
  1

  
  
  PowerBuilder

  //Use the label of the item being populated

  1	//Use the label of the item being populated

  
  
  PowerBuilder

  // as the retrieval argument

  1	// as the retrieval argument

  
  
  PowerBuilder

  This.GetItem(handle, tvi1)

  1	This.GetItem(handle, tvi1)

  
  
  PowerBuilder

  ll_rowcount = ids_info.Retrieve(tvi1.Label)

  1	ll_rowcount = ids_info.Retrieve(tvi1.Label)

  
  
  1

  
  
  PowerBuilder

  //Use information retrieved from the database

  1	//Use information retrieved from the database

  
  
  PowerBuilder

  //to populate the expanded item

  1	//to populate the expanded item

  
  
  PowerBuilder

  FOR ll_row = 1 to ll_rowcount

  1	FOR ll_row = 1 to ll_rowcount

  
  
  PowerBuilder

  This.InsertItemLast(handle, &

  1	This.InsertItemLast(handle, &

  
  
  PowerBuilder

  ids_info.GetItemString(ll_row, &

  1	ids_info.GetItemString(ll_row, &

  
  
  PowerBuilder

  music_title'), 2)

  1	music_title'), 2)

  
  
  PowerBuilder

  LOOP

  1

  LOOP

Destroying DataStore instances

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

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