Question

In the above image, child is a ContentPresenter. Its Content is a ViewModel. However, its ContentTemplate is null.

In my XAML, I have a TabControl with the following structure:

<local:SuperTabControlEx DataContext="{Binding WorkSpaceListViewModel}"
 x:Name="superTabControl1" CloseButtonVisibility="Visible" TabStyle="OneNote2007" ClipToBounds="False" ContentInnerBorderBrush="Red" FontSize="24" >
            <local:SuperTabControlEx.ItemsSource>
                <Binding Path="WorkSpaceViewModels" />
            </local:SuperTabControlEx.ItemsSource>

                <TabControl.Template>
                <ControlTemplate
                    TargetType="TabControl">
                        <DockPanel>
                            <TabPanel
                            DockPanel.Dock="Top"
                            IsItemsHost="True" />
                            <Grid
                            DockPanel.Dock="Bottom"
                            x:Name="PART_ItemsHolder" />
                        </DockPanel>
                        <!-- no content presenter -->
                    </ControlTemplate>
                    </TabControl.Template>

            <TabControl.Resources>
            <DataTemplate DataType="{x:Type vm:WorkSpaceViewModel}">

            ....

WorkSpaceViewModels is an ObservableCollection of WorkSpaceViewModel. This code uses the code and technique from Keeping the WPF Tab Control from destroying its children.

The correct DataTemplate – shown above in the TabControl.Resource – appears to be rendering my ViewModel for two Tabs.

However, my basic question is, how is my view getting hooked up to my WorkSpaceViewModel, yet, the ContentTemplate on the ContentPresenter is null? My requirement is to access a visual component from the ViewModel because a setting for the view is becoming unbound from its property in the ViewModel upon certain user actions, and I need to rebind it.

Answer 1

The DataTemplate is “implicitly” defined. The ContentPresenter will first use it’s ContentTemplate/Selector, if any is defined. If not, then it will search for a DataTemplate resource without an explicit x:Key and whose DataType matches the type of it’s Content.

This is discussed here and here.

The View Model shouldn’t really know about it’s associated View. It sounds like there is something wrong with your Bindings, as in general you should not have to “rebind” them. Either way, an attached behavior would be a good way to accomplish that.