Otherwise, the node must be a photograph node. in Visual C#.NET

Generation ECC200 in Visual C#.NET Otherwise, the node must be a photograph node.

As you can see, we take advantage of the LoadAlbumData and LoadPhotoData methods implemented in chapter 14. By encapsulating our load functionality in a method, we are able to reuse the methods here with no changes. Both of these methods are based on a file path from which to load the data, and we make use of this fact here to specify the appropriate data associated with the selected tree node. For a toplevel node this is an album directory. For an album node this is an album file which is loaded as a new PhotoAlbum object. For a photograph node, this is the image file, although we do not make use of this fact here. Astute readers will realize that there is some inefficiency here since we have separated the logic for updating our two views. For instance, when an album node is expanded and selected, we open the album to load the collection of photographs in the treeViewMain_BeforeExpand method, and then open the album again to update the contents of the ListView control from the treeViewMain_AfterSelect method. This is the result, in part, of how we have separated our discussion of the two controls. In a production program, you would likely want to merge these efforts to ensure that an album is only opened one time for each update. One situation we will fix is the behavior of the OnLoad method. The method performs the following tasks:

The InitTreeData method is called, which does the following: a Creates and selects the top level node, b Creates tree nodes for each album in the default album directory. As a result of selecting the top-level node, the treeViewMain_After-Select event handler is called, which does the following: a Calls LoadAlbumData to populate the ListView control. Back in the OnLoad method, the LoadAlbumData method is called to initialize the ListView control.

Clearly the second call to LoadAlbumData is no longer required, so we can remove it from our program.

UPDATE THE ONLOAD METHOD Action 7 Modify the OnLoad method to only initialize the TreeView control. Result

protected override void OnLoad(EventArgs e) { . . . // Initialize the contents of the form InitTreeData(); }

This completes the update of the list view as the contents of the tree view are modified. You can compile and run the application to verify that the ListView contents changes as different nodes are selected. Our next topic is to update the contents of the TreeView control based on user interactions with the list view items. 15.4.2 REVISITING THE LIST VIEW The contents of our ListView control can be modified directly by the user through the control itself and through the menu bar items. There are three actions a user can perform to alter the list contents:

Select the Albums menu item under the View menu. This invokes a Click event for the menu, and our menuAlbums_Click event handler. Select the Photos menu item under the View menu, which can only be done when an item representing an album is selected in the list view. This invokes a Click event for the menu, and our menuPhotos_Click event handler. Double-click on an item in order to activate it. This invokes the ItemActivate event, and our listViewMain_ItemActivate event handler.

We will handle each of these actions by selecting the appropriate node in our TreeView control. This permits the tree view to be in charge of ensuring that all controls on the form display the proper information based on the currently selected node. This is a good general mechanism that can be employed in any application. Let s take a moment to consider what the behavior should be for each of these actions. These are summarized in the following table.

Result of user actions modifying the ListView control Action Select the Albums menu item. Select the Photos menu item. Result in TreeView The top-level Default Albums node should be selected. The tree node corresponding to the current album should be selected. Result in ListView The collection of albums from the default album directory should be displayed. The collection of photographs for the current album should be displayed. The contents of the item should be displayed.

Double-click on an item The tree node corresponding to the in the list view. activated item should be visible and selected.

As you can see, all three actions should result in the selection of a node in the tree. This will cause the AfterSelect event to occur, which will invoke our treeViewMain_AfterSelect event handler. This handler will, in turn, cause the proper set of items to appear in the ListView control, as described in the previous table. As a result, we simply need to modify the behavior for these three actions to select the proper tree node, and our existing code will do the rest. We will begin with our Albums menu item. NODE SELECTION 509

UPDATE THE MENUALBUMS_CLICK EVENT HANDLER Action 1 Locate the menuAlbums_Click event handler in the MainForm.cs code window. Modify this handler to select the Default Albums tree node.