Question

I am doing a WPF application with a TabControl. At the beginning I had a TabControl bound to ObservableCollection of TabBase items, where TabBase is a base class for tab viewmodel:

<TabControl
    IsSynchronizedWithCurrentItem="True"
    ItemsSource="{Binding Tabs}"
    ItemTemplate="{StaticResource ClosableTabTemplate}"
...
public ObservableCollection<TabBase> Tabs { get; private set; }
...
public abstract class TabBase : ViewModelBase
...
public abstract class ViewModelBase : INotifyPropertyChanged
{
    public virtual string DisplayName { get; protected set; }
...
<DataTemplate x:Key="ClosableTabTemplate">
    <DockPanel Width="120">
        <Button
            Command="{Binding Path=CmdClose}"
            Content="X"
            />
        <ContentPresenter 
            Content="{Binding Path=DisplayName}">
        </ContentPresenter>
    </DockPanel>
</DataTemplate>

But I’ve faced with an issue when I switch tabs it looks like current tab is being created each time, even if it was already opened before. Searching thru StackOverflow I’ve found the solution here with reference to here. I’ve replaced using of declarative ItemsSource with dynamic creation of tabs from code. Tabs switching performance issue was resolved, but tab headers have lost link to template, so instead of tab header with caption and close button I see just a little tab header without anything. Playing a bit with tab creation code, I was able to restore tab size and close button, but without binding – there is no caption and close button doesn’t work (5 lines with item.Header restored original tab size):

    private void AddTabItem(TabBase view)
    {
        TabItem item = new TabItem();
        item.DataContext = view;
        item.Content = new ContentControl();
        (item.Content as ContentControl).Focusable = false;
        (item.Content as ContentControl).SetBinding(ContentControl.ContentProperty, new Binding());

        item.Header = new ContentControl();
        (item.Header as ContentControl).DataContext = view;
        (item.Header as ContentControl).Focusable = false;
        (item.Header as ContentControl).SetBinding(ContentControl.ContentProperty, new Binding());
        item.HeaderTemplate = (DataTemplate)FindResource("ClosableTabTemplate");

        tabControl.Items.Add(item);
    }

The question is, how can I make ItemTemplate working for TabControl without ItemsSource binding?

Answer 1

When you explicitly set your item.Header to a ContentControl, the HeaderTemplate is now using that object as its DataContext. Normally, the Header property would get your ViewModel and a ContentPresenter would take that (non-Visual) object and apply the HeaderTemplate to it. You’ve now pushed your ViewModel down a level in the hierarchy so the template is not being applied at the same place as the data. Moving either one should fix the Binding issues but one or the other may work better for your situation:

item.Header = view;

or

(item.Header as ContentControl).ContentTemplate = (DataTemplate)FindResource("ClosableTabTemplate");