Question

I have a datagrid nested inside the ItemTemplate of a ListBox. I’m trying to display a tree like data structure using this. My classes are as follows.

The object in my data context contains a List<Section> named Sections, my ListBox is bound to this. Each Section contains a List<Item> named Items, the DataGrid in eac ItemTemplate is bound to this.

When I run the app, I get a null reference exception from the XAML at the line with the binding. Is there a better/alternative way of doing this, or am I missing a trick with the binding?

<Window.Resources>
    <CollectionViewSource x:Key="SectionSource" /><!-- this is initialized and filled with an ObservableCollection<Section> Sections when the window loads-->
</Window.Resources>

<ListBox x:Name="lstIngredients" ItemsSource="{Binding Source={StaticResource SectionSource}}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <DataTemplate.Resources>
                <CollectionViewSource x:Key="itemsSource" Source="{Binding Items}"/>
            </DataTemplate.Resources>

<DataGrid x:Name="dgItems" IsReadOnly="false" AutoGenerateColumns="False" SelectionMode="Single" SelectionUnit="FullRow" IsSynchronizedWithCurrentItem="True" 
    DataContext="{Binding}"
    ItemsSource="{Binding Source={StaticResource Items}}"
    EnableRowVirtualization="false" 
    VirtualizingStackPanel.VirtualizationMode="Standard"
        <DataGrid.Columns>
<DataGridTemplateColumn Width="2*" Header="{lex:LocText ChickenPing.Shared:Strings:Measurement}">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <TextBlock x:Name="quantity" Text="{Binding Measurement}" TextTrimming="CharacterEllipsis" TextAlignment="Left"/>
                    <!-- Null reference on this line caused by the binding. If I set this to any DependencyProperty on an Item object, I get a null reference-->
                </DataTemplate>

Answer 1

I eventually tracked this down to an event which was set in one of the TemplateColumns. Switching the event from

<TextBlock x:Name="quantity" Text="{Binding Measurement}" GotFocus="txt_GotFocus" />

to

<Style x:Key="FocusableTextbox" TargetType="{x:Type TextBox}"> 
    <EventSetter Event="GotFocus" Handler="txt_GotFocus" /> 
</Style>
...
<TextBlock x:Name="quantity" Text="{Binding Measurement}" Style={StaticResource FocusableTextbox} />