ComboBox empty. WPF Application

Hi everybody,

I'm doing a WPF Application. In my XAML page i created a very simply  ComboBox. The problem is the my ComboBox is always empty (white). I can't see any selection.

I made the program

Me.ComboBox1.Items.Add("sfgs")

Me.ComboBox1.Items.Add("sfgs")

Me.ComboBox1.Items.Add("sfgs")

.... and it doesn't work.  Why?