![]() all other nodes are generated by the TreeViewItems themselves (Remember that the TreeViewItems are ItemsControl as well :)). Because the Treeview only generate root nodes. You would be wondering, But wouldn’t this make all TreeViewItems root nodes?!!? And the answer is, NO. So the most important part is where we set the Attached property IsRootNode to true (Please also note that by default the Attached property is set to false). You could grab the exception and use it to reflect this in the interface in one way or another.Public class MyTreeView : TreeView Notice that the loop where we add each child folder is in a try.catch block - this is important, because some paths might not be accessible, usually for Represents, and then we get a list of child directories, which we add to the clicked item, once again using the CreateTreeItem() method. We now use the items Tag property to get a reference to the DriveInfo or DirectoryInfo instance that the current item To check whether this item has already been loaded, by checking if the child items currently consists of only one item, which is a string - if so, we haveįound the "Loading." child item, which means that we should now load the actual contents and replace the placeholder item with it. As already mentioned, this event is raised each time a TreeView item is expanded, so the first thing we do is Next up is the TreeViewItem_Expanded event. How we add a child item to the Items collection, in the form of a string with the text "Loading.". ![]() Notice that we use a custom method to create the TreeViewItem, called CreateTreeItem(), since we can use the exact same method when we want to dynamically add a child folder later on. Instance to the Tag property, so that we can later retrieve it. In Code-behind, we start by adding each drive found on the computer to the TreeView control. To be aware of to load its child items on demand. This event gets called each time an item is expanded, which we need That this is indeed the TreeViewItem and not the TreeView itself, but because the event bubbles up, we are able to just capture it in one place for theĮntire TreeView, instead of having to subscribe to it for each item we add to the tree. The XAML is very simple and only one interesting detail is present: The way we subscribe to the Expanded event of TreeViewItem's. Private TreeViewItem CreateTreeItem(object o) If(( = 1) & (item.Items is string))ĮxpandedDir = (item.Tag as DriveInfo).RootDirectory ĮxpandedDir = (item.Tag as DirectoryInfo) įoreach(DirectoryInfo subDir in expandedDir.GetDirectories()) TreeViewItem item = e.Source as TreeViewItem Public void TreeViewItem_Expanded(object sender, RoutedEventArgs e) Public partial class LazyLoadingSample : WindowĭriveInfo drives = DriveInfo.GetDrives() Namespace WpfTutorialSamples.TreeView_control So how is it accomplished? Let's have a look at the code: You try to expand it, as it can be seen on the next screenshot: If a folder is empty, it will be shown as empty once You can now start expanding the nodes, and the application will automatically load the sub folders. This is how our application looks when it starts - by that time, we have only obtained a list of available drives on the computer: To achieve this, we simply add a dummy folder to each drive or child folder, and then when the user expands it, we remove the dummy folder and replace it This is the perfect task for a lazy-loaded TreeView, where child folders are only loaded on demand. Through each drive and each drives child folders could become extremely time consuming and your TreeView would soon consist of a lot of nodes, with a high Levels and child nodes and a great example of this, is the folder structure of your Windows computer.Įach drive on your Windows computer has a range of child folders, and each of those child folders have child folders beneath them and so on. This is especially useful if you have a very deep tree, with lots of You want to delay the loading of a nodes child items until they are actually needed. The usual process when using the TreeView is to bind to a collection of items or to manually add each level at the same time. The TreeView control: Lazy loading TreeView items
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