WPF events, commands or using both

Question

Hello, I am constructing my app infra structure, and finding it hard to achieve a very basic behavior - I want to raise events from different user controls in the system and being able to catch those events on some other user controls that listens to them. For example i have a user control that implements a TreeView. I have another user control that implmements a ListView. Now, i want my ListView to listen to the TreeView, and when the selection is changed on the TreeView, i want to repopulate my ListView accordingly. I also want this to happen even if the ListView is not located within the TreeView on the WPF logical tree.

PLEASE HELP!!

Thanks, Oran

Answer 1

This is the point where the added complexity of MVVM (Model-View-ViewModel pattern) can start to pay off. What you need is a publish/subscribe infrastructure, and MVVM Light has that, along with good MVVM structure that doesn't get overly complex. Prism is another good WPF/Silverlight infrastructure foundation with publish and subscribe support.

Answer 2

Use data binding.

If the content of the list view is stored inside the object shown in the tree view you can just bind into the tree SelectedItem property.

Otherwise bind the tree SelectedItem to a property in your view models (or your window!) and in the setter of this property change the list that is bound to the list view ItemSource property.

You can see the technique in this series on my blog the post I linked to is the last post with the code download link, you'll need to read from the beginning of the series if you want the full explanation.

EDIT: Here's how I did it in one project: (the GridView definition removed since it's not relevant here)

    <TreeView 
        Name="FolderTree" 
        Width="300" 
        ItemsSource="{Binding Root.SubFolders}"
        ItemTemplate="{StaticResource FolderTemplate}"/>
    <ListView 
        Name="FileView"
        ItemsSource="{Binding ElementName=FolderTree, Path=SelectedItem.Files}">
    </ListView>

The list bound into the tree view's ItemsSource is of objects that have 3 properties: Name (that is bound to a TextBlock in the FolderTemplate), SubFolders (that is likewise bound to the HierarchicalDataTemplate.ItemsSource property) and Files that is bound to the ListView using {Binding ElementName=FolderTree, Path=SelectedItem.Files}

Note that non of the lists are observable collections (because in this project they never change) but are loaded lazily (on-demand) by the properties getters (because in this project they are expensive to load).