Question

I have a TreeView databound to a CollectionViewSource Groups collection. This is so that I can display the data using the power of the CollectionViewSource, and the data itself also has a hierarchical structure, which is why I need the TreeView. I have a second control which is bound to the SelectedItem of the TreeView.

The problem is that when the group header is selected, the program crashes with the following exception.

{"A TwoWay or OneWayToSource binding cannot work on the read-only property 'Name' of type 'MS.Internal.Data.CollectionViewGroupInternal'."}

The objects in my TreeView contain a Name property that is two way bound in another control. The binding engine seems to find the Name property for the Group and attempt to bind to that. How can I prevent this exception from occuring? I would like for the rest of my program to treat it as if nothing is selected when the group header is selected, or disallow selecting the group header all together. Below is a simplified version of the code.

        <TreeView
            x:Name="CustomersTree"
            ItemsSource="{Binding CustomersViewSource.Groups}"
            ItemTemplate="{StaticResource CustomerGroupsTemplate}">

        <MyUserControl DataContext="{Binding ElementName=CustomersTree, Path=SelectedItem, Mode=OneWay}" />

<HierarchicalDataTemplate x:Key="CustomerGroupsTemplate" ItemsSource="{Binding Path=Items}" ItemTemplate="{StaticResource CustomerTreeItemTemplate}">
    <TextBlock Text="{Binding Path=Name}"/>
</HierarchicalDataTemplate>

<HierarchicalDataTemplate x:Key="CustomerTreeItemTemplate" ItemsSource="{Binding Customers}">
    <StackPanel>
        <Image Source="{Binding ImageSource}" />
        <TextBlock Text="{Binding Path=Name}" />
    </StackPanel>
</HierarchicalDataTemplate>

To be clear, the error is a result of the binding in the CustomerGroupsTemplate as far as I can tell, and changing this binding to OneWay results in the same error. The information in the tree shows up the way it is expected to, it is only when a group header is selected that the exception occurs.

Answer 1

The problem was the result of a two way binding within the user control. I ended up using a converter to check for the type of the object being bound, ignoring it if it wasn’t the object I wanted.