Trap Error on SelectedItem change

[Joel Palmer]

I have the SelectedItem of my TreeListView bound to a property.  However, if conditions aren't met that Property will throw an exception.  How do I capture that exception?  Is it a Binding error?  Is it a Data error?  How do I trap and expose it?  DataError and GiveFeedback events don't seem to give me anything to trap.

 

<telerik:RadTreeListView
    x:Name="treeListView"
    AutoGenerateColumns="False"
    HorizontalAlignment="Stretch"
    VerticalAlignment="Stretch"
    CanUserFreezeColumns="False"
    CanUserReorderColumns="False"
    SelectionMode="Single"
    Grid.Row="1"
    Margin="5"
    IsReadOnly="{Binding IsReadOnly}"
    ItemsSource="{Binding Hierarchy, Mode=TwoWay}"
    SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
    AutoExpandItems="True"
    ShowGroupPanel="False"
    IsFilteringAllowed="False"
    ShowColumnHeaders="False"
    IsExpandedBinding="{Binding IsExpanded, Mode=TwoWay}" DataError="treeListView_DataError" GiveFeedback="treeListView_GiveFeedback">

    <telerik:RadTreeListView.ChildTableDefinitions>
        <telerik:TreeListViewTableDefinition
            ItemsSource="{Binding Children}"/>
    </telerik:RadTreeListView.ChildTableDefinitions>
    <telerik:RadTreeListView.Columns>

        <telerik:GridViewDataColumn
            DataMemberBinding="{Binding Name, Mode=TwoWay}"
            CellTemplate="{StaticResource TreeNodeTemplate}"
            IsReadOnly="False"
            Width="*"/>

        <telerik:GridViewComboBoxColumn
            x:Name="itemTypeColumn"
            Header="Item Type"
            DataMemberBinding="{Binding ItemTypeID, Mode=TwoWay}"
            DisplayMemberPath="Name"
            SelectedValueMemberPath="ID"
            SortMemberPath="Order"
            SortingState="Ascending"
            ItemsSource="{Binding TypeModel.Items, Mode=TwoWay}"
            IsReadOnly="True"
            Width="150"/>

        <telerik:GridViewDataColumn
            DataMemberBinding="{Binding IsActive, Mode=TwoWay}"
            Header="Include"/>

    </telerik:RadTreeListView.Columns>
</telerik:RadTreeListView>

[Joel Palmer]

To provide more context, I have a MainWindow --> UserControl --> TreeListView.  The MainWindow has a ModelView DataContext that has several sub-ModelViews.  So, the DataContext glues multiple UserControls together. 
When I select an item on the TreeListView control, the Property fires a "PropertyValueChanging" event where I perform a Save on another control in the UI.  Then, the property value is updated and I fire a "PropertyValueChanged" event where I then perform a Load on another control in the UI.

Problem is, if an exception is thrown in the PropertyValueChanging event handler, I want to expose the exception to the user and I want the TreeListView to stay on the "old" item; not the just-clicked item.  I have figured out how to expose the error to the user but I don't know how to prevent the TreeListView from moving to the newly selected node.

[Ivan Ivanov]

Hello,

As far as I can understand, you perform the validation logic in the ViewModel. So that, RadTreeListView's SelectedItem property is updated first and then the bound property may throw an exception. Thus you need to process the exception and set the valid value to the SelectedItem property manually. Is it possible for you to carry out this validation in RadTreeListView's SelectionChaning event, so that you can prevent the SelectedItem property from changing its value if it is an invalid one?

Regards,
Ivan Ivanov
Telerik