#Wpf mvvm treeview example how to#
#Wpf mvvm treeview example code#

Each time the recursive method is called, a new frame is pushed onto the callstack, and it keeps track of the local variable values for you. Most recursive algorithms store their state on the callstack. I have plenty of experience building recursive algorithms that walk over trees, but I had never built one like this. After finding the first match, the next time I perform the search, it should only load as many items as necessary to find the next matching item. So I thought that I had to create a custom search algorithm that would perform the search and only load as many items into memory as necessary to find the first matching item. Since I (incorrectly) thought that it walked down the entire data tree upon creation, performing a search with it would have forced the entire tree to be loaded into memory at once. The UI looks like this:īased on my misunderstanding of how a yield-based enumerator works, I thought it would have been bad to use it in this situation. I took the load-on-demand sample and added in the ability to search the items. As we will see later, this is entirely untrue, but I, too, can be an idiot sometimes. I was under the false assumption that it was executing the search logic to completion when the FindMatches method is called, and storing the results in a collection of some type. I decided to implement a solution.Īt the time, I misunderstood exactly how my search method used the ‘yield’ keyword. Aside from the fact that performing a search that produces no matching items will force all of the items to be loaded it is a reasonable question.

#Wpf mvvm treeview example how to#

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.

#Wpf mvvm treeview example code#

(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. 1: using System ġ7: /// 18: /// Interaction logic for Window1.xaml 19: /// 20: public partial class Window1 : WindowĢ2: static public List stateList = new List() Ģ9: citylist1.Add( new City(' Baltimore', true)) ģ0: citylist1.Add( new City(' Frederick', true)) ģ1: citylist1.Add( new City(' Rockville', true)) Ĥ0: citylist2.Add( new City(' Los Angeles', true)) Ĥ1: citylist2.Add( new City(' Sacramento', false)) Ĥ2: citylist2.Add( new City(' San Francisco', true)) Ĥ3: citylist2.Add( new City(' San Diego', false)) ĥ2: citylist3.Add( new City(' Houston', true)) ĥ3: citylist3.Add( new City(' Dallas', false)) ĥ4: citylist3.Add( new City(' Austin', false)) ĥ5: citylist3.I must admit, I had never really become too comfortable with the C# ‘yield’ keyword until recently.

Here is complete C# code of this program. Here is simple XAML code to insert check box in tree control. Using check box is very similar to using any other control inside the data template and hierarchical data template.