The value converter contains the names of the icon resources, and it actually loads a BitmapSource using those hard-coded resource identifiers. For example, if the value converter receives “C:\” as the header text, it returns the “drive” icon. That binding has a converter which looks for a backslash character in the header text, and if it finds one that means the item is at the root level (i.e. A TreeViewItem’s Image element, which displays an icon, has its Source property bound to the Header of the TreeViewItem. The way he implemented the logic which determines which icon to use involves a value converter. In his demo, the root level items in the tree have a “drive” icon, and all other items have a “folder” icon. It is a nice gentle intro to lazy-loading the WPF TreeView, and I highly recommend checking it out.Īfter reading Sacha’s great article I felt that something was amiss. Sacha Barber recently posted an article to CodeProject titled “ A Simple WPF Explorer Tree.” The article shows how to lazy-load the TreeView control with the directory structure on your machine. This is where the idea of a ViewModel comes into play.Ħ Comments | Reading Material, Theoria | Tagged: treeview, viewmodel, wpf | Once you stop treating the TreeView as a place to put data, and start treating it as a place to show data, everything starts working smoothly. All of the problems listed in the previous section derive from trying to go against the grain and treat the UI as a backing store. WPF is great because it practically requires you to separate an application’s data from the UI. If you have ever thought that the WPF TreeView is too complicated and doing anything non-trivial with it is difficult, think again! Over the past few days I have been solidifying my TreeView programming techniques, thanks to an invigorating e-mail thread with Sacha Barber, and it all culminated in this article: In a surge of Mahler-inspired geekery, I wrote and published what I consider to be one of my best WPF articles. In WPF, the TreeView control provides a view of a tree. It might seem like a minor difference, but, in my opinion, it represents a significant change of mindset. We can remain focused on the tree data structure, it’s behavior, it’s state, and just tell the TreeView how we want to view the tree. We declare all of this in XAML, and let TreeView handle all the details of applying our styles and templates. We can provide in-depth customizations for how the TreeView renders the items, by setting properties such as ItemContainerStyle to affect properties of every TreeViewItem, and ItemTemplate to specify what each item should look like and where its child items come from. We are not required to focus much on the TreeView, but more on the data we actually care about. At that point, the TreeView will do all the grunt work of creating TreeViewItems and hooking them together for us. The fact that the WPF TreeView supports data binding allows us to create a tree data structure, perhaps of custom ViewModel objects, and provide it to the TreeView control’s ItemsSource property. We can use the TreeView in our WPF programs to literally provide a view of a tree. Granted, at the end of the day, it still has a tree data structure consisting of TreeViewItem objects, but the similarities end there. The WPF TreeView control is very different. WinForms should have a Tree control instead of a TreeView control. By the same reasoning, we should call the Menu a MenuView and the ComboBox a ComboBoxView, but that is not the case. One could argue that the WinForms TreeView control’s name is a misnomer, because it can only show its own TreeNodes. You create a tree data structure in the control, where each node in the tree is of type TreeNode, and the control renders those nodes. The WinForms TreeView control is not really providing a “view” of a tree: it is the tree. After a while, I got used to the name and never gave it much thought, until now. NET 1.0 era, I don’t think any other control had the word “View” tacked onto the end of its name, except for ListView. Why not call it the Tree control? Why did they add the word “View” to the end? At the time, the. When I first started learning about Windows Forms, I thought the TreeView control had a strange name. My recent article about it, which, by the way, is my wedding gift to Sacha Barber, discusses how the ideal way of working with a TreeView is to bind it to a ViewModel, and then program against the ViewModel. I have been thinking a lot about the WPF TreeView control lately.
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