How to set an (unbound) SelectedIndex for a WPF Windows.Controls.ComboBox?

Question

Hi,

This should be easy but it's not working. I have a WPF combobox bound to a List.

• The items populate just fine
• I want the first item to show on startup.
• However! If the SelectedIndex is set to 0 or anything else it stays blank.

Wozzup?

Code Result: No item selected when the form loads. :-(

Answer 1

I think the problem will be that the ComboBox's items are being populated in a background thread (by the binding) and thus at the time you're setting SelectedIndex to 0 there aren't any items in the list.

If that's the case, the trick is to handle the StatusChanged event on the ComboBox's ItemContainerGenerator and set your selected index there:

comboBox1.ItemContainerGenerator.StatusChanged += ItemContainerGenerator_StatusChanged;

void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
{
    if (comboBox1.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)
    {
        return;
    }

    // unhook the event - we don't need it now
    comboBox1.ItemContainerGenerator.StatusChanged -=
        ItemContainerGenerator_StatusChanged;

    comboBox1.SelectedIndex = 0;
}

Answer 2

I tend to use ObservableCollection based data types for the DataContext.