TabControl with Add New Tab Button (+)

Question

What is the proper way of adding a '+' button tab at the end of all the tab items in the tab strip of a tab control in WPF?

1. It should work correctly with multiple tab header rows.
2. It should be at the end of all tab items
3. Tab cycling should work correctly (Alt + Tab), that is, the + tab should be skipped.
4. I shouldn't have to modify the source collection I am binding to. That is, the control should be reusable.
5. The solution should work with MVVM

To be more precise, the button should appear exactly as an additional last tab and not as a separate button somewhere on the right of all tab strip rows.

I am just looking for the general approach to doing this.

Google throws many examples, but if you dig a little deep none of them satisfy all the above five points.

Answer 1

An almost complete solution using IEditableCollectionView:

ObservableCollection<ItemVM> _items;
public ObservableCollection<ItemVM> Items
{
    get
    {
        if (_items == null)
        {
            _items = new ObservableCollection<ItemVM>();
            var itemsView = (IEditableCollectionView)CollectionViewSource.GetDefaultView(_items);
            itemsView.NewItemPlaceholderPosition = NewItemPlaceholderPosition.AtEnd;
        }

        return _items;
    }
}

private DelegateCommand<object> _newCommand;
public DelegateCommand<object> NewCommand
{
    get
    {
        if (_newCommand == null)
        {
            _newCommand = new DelegateCommand<object>(New_Execute);
        }

        return _newCommand;
    }
}

private void New_Execute(object parameter)
{
    Items.Add(new ItemVM());
}

<DataTemplate x:Key="newTabButtonContentTemplate">
    <Grid/>
</DataTemplate>

<DataTemplate x:Key="newTabButtonHeaderTemplate">
    <Button Content="+"
        Command="{Binding ElementName=parentUserControl, Path=DataContext.NewCommand}"/>
</DataTemplate>

<DataTemplate x:Key="itemContentTemplate">
    <Grid/>
</DataTemplate>

<DataTemplate x:Key="itemHeaderTemplate">
    <TextBlock Text="TabItem_test"/>
</DataTemplate>

<vw:TemplateSelector x:Key="headerTemplateSelector"
                           NewButtonTemplate="{StaticResource newTabButtonHeaderTemplate}"
                           ItemTemplate="{StaticResource itemHeaderTemplate}"/>

<vw:TemplateSelector x:Key="contentTemplateSelector"
                            NewButtonTemplate="{StaticResource newTabButtonContentTemplate}"
                            ItemTemplate="{StaticResource itemContentTemplate}"/>

<TabControl ItemsSource="{Binding Items}"
        ItemTemplateSelector="{StaticResource headerTemplateSelector}"
        ContentTemplateSelector="{StaticResource contentTemplateSelector}"/>

public class TemplateSelector : DataTemplateSelector
{
    public DataTemplate ItemTemplate { get; set; }
    public DataTemplate NewButtonTemplate { get; set; }

    public override DataTemplate SelectTemplate(object item, DependencyObject container)
    {
        if (item == CollectionView.NewItemPlaceholder)
        {
            return NewButtonTemplate;
        }
        else
        {
            return ItemTemplate;
        }
    }
}

Enter code here

It's almost complete, because the tab cycle doesn't skip the '+' tab, and will show empty content (which is not exactly great, but I can live with it until a better solution come around...).