Shortly after publishing the article, two people asked how to have a lazy-loaded tree with search capabilities. That demo does not provide the ability to search. The article also has a demo program that lazy-loads each item’s children. (Click on the image to view the source code at full-size) The search logic uses the yield keyword, as seen below: In my ‘ Simplifying the WPF TreeView by Using the ViewModel Pattern‘ article I have a demo program that lets the user search through the items in a TreeView. Beyond that vague understanding, I was not too familiar with it. A compiler-generated implementation of IEnumerator exists behind the scenes, which implements the logic to produce the enumerator you declared in C#. I also knew that the C# compiler interprets the code in a method that uses the yield keyword. I knew that it was introduced in C# 2.0 as a means of simplifying the creation of an enumerator. The easiest way to create a command is probably to use a DelegateCommand (google it to get an implementation as it is not part of WPF).Ī perhaps better alternative that allows two-way binding without the clunky command is to use BindableSelectedItemBehavior provided by Steve Greatrex here on Stack Overflow.I must admit, I had never really become too comfortable with the C# ‘yield’ keyword until recently. When the selected item of the tree view changes the Execute method on the command is called with the selected item as the parameter. You will have to add a property SetSelectedItemCommand on the DataContext of the TreeView returning an ICommand. Here I have added an EventTrigger that will invoke a command each time the selected item changes in the tree: However, to be able to do it "MVVM style" you need to use a Blend behavior (available as various NuGet packages - search for "blend interactivity"). If you don't want to track selection on each individual item on the tree you can still use the SelectedItem property on the TreeView. To expose an SelectedItem property on your parent view-model (the one you bind to the TreeView and that has a collection of child view-models) you can implement it like this: public ChildViewModel SelectedItem Not having a view-model means that you are using your model objects as view-models, but for this to work these objects require an IsSelected property. If you don't have a view-model for each item in the tree, well, then you should get one. On the other hand if you set IsSelected to true on a view-model the node in the tree for that view-model will be selected. Note that these properties work both ways so if the user selects a node in the tree the IsSelected property of the view-model will be set to true. Your view-model then has to expose a boolean IsExpanded property. If you want to be able to control if a particular TreeViewItem is expanded you can use a setter for that property too: Your view-model (the view-model for each item in the tree) then has to expose a boolean IsSelected property. To do what you want you can modify the ItemContainerStyle of the TreeView: So, my overall question is: "Is there a simple way to get the selected item to my view model?" There was also a seemingly elegant suggestion to do something like this: Īnd I asked this question: "How can your a view model get this information? I get that ContentPresenter holds the selected item, but how do we get that over to the view model?" But there is no answer yet. But I can't use it because the compiler complains that it's read-only. What's frustrating to me is that read-only is just fine I don't want to change it via code. Note: There is a SelectedItem property on the TreeView`, but it's read-only. Is there a simple way to get the selected item to my view model? However, I've found various ways on SO to get the selected item, and many are convoluted and difficult. This correctly shows servers by environment (dev, QA, prod). This is all within the UserControl.Resources tag: So far, I have this XAML, which isn't very intuitive on its own. I do not need to set the selected item from code I just need my view model to know which item the user selected. Through a bunch of research, I was able to get the TreeView` control working, but I simply cannot find the "proper" way to get the selected item to the view model. So someone suggested using a WPF TreeView, and I thought: "Yeah, that seems like the right approach." Now, hours and hours later, I simply can't believe how difficult it has been to use this control.
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