Question

I have this very simple Combobox in my XAML:

<ComboBox Name="cmb1" Width="200" Height="23" ItemsSource="{Binding}" />

and this is my code behind:

public class Test //: System.Windows.DependencyObject
{
    public string Name { get; set; }

    public override string ToString() { return Name; }
}

public MainWindow()
{
    InitializeComponent();

    var col = new ObservableCollection<Test>();
    cmb1.DataContext = col;
    col.Add(new Test { Name = "A" });
    col.Add(new Test { Name = "B" });
    col.Add(new Test { Name = "C" });
    col.Add(new Test { Name = "D" });
}

As long as Test class is NOT inherited from DependencyObject everything is fine. But when it is inherited, ComboBox does not show current item when it is not expanded.
Current Item is selected when I click on ComboBox and see its drop-box.

Answer 1

This was the answer by karmicpuppet in a now deleted question:

This is interesting. Well, I’ve looked
at the ComboBox class using Reflector
and I see that in the
ComboBox.UpdateSelectionBoxItems()
method, part of it does something
like:

If ItemTemplate, ItemTemplateSelector,
and ItemStringFormat were not set, and
selected item is a DependencyObject
that is not derived from UIElement,
call the ExtractString(selectedItem)
method.

The ComboBox.ExtractString(dObj)
method, on the other hand, apparently
checks to see if the selectedItem
(which is a DependencyObject) is
either a TextBlock, a Visual, or a
TextElement to display the appropriate
string. Otherwise, it will return
string.Empty.

So the easiest solution would be to set this on the Combobox:

ItemStringFormat="{}{0}"