How to expand RadTreeView using MVVM approach?

[Dmitry]

Hello. I write WPF MVVM Prism 6 multimodule application. In some View (let us call it PeppyView) I have RadTreeView which bound to ObservableCollection located in PeppyViewModel. This radTreeView is populated with data from this ObservableCollection. In turn, the ObservableCollection is populated with data from binary *.DAT file when user is clicking on the 'Deserialize' RadButton. After populating with the data my RadTreeView is shown as collapsed RadTreeView. But I need that my RadTreeView is shown as expanded after its populating with data. Because ViewModel has to have no knowlage about the View in MVVM I can't call RadTreeView.ExpandAll method from ViewModel code. So how can I expand RadTreeView in my case? Is there a way to map UI control's method to ViewModule and call it there?

[Martin Ivanov]

Hello Yaroslav,

In order to achieve your requirement you can use an implicit style targeting RadTreeViewItem and use it to set the IsExpanded property of all items to True. 

<Window.Resources>
    <Style TargetType="telerik:RadTreeViewItem">
        <Setter Property="IsExpanded" Value="True" />
    </Style>
</Window.Resources>

Or bind the IsExpanded property to a property from the items view models and set it while creating them.

<Window.Resources>
    <Style TargetType="telerik:RadTreeViewItem">
        <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
    </Style>
</Window.Resources>

You can find those approaches described in the Expanding and Collapsing Items help article.

I hope this helps.

Regards,
Martin
Telerik by Progress