ComboBox ItemsSource changed => SelectedItem is ruined

Question

Ok, this has been bugging me for a while now. And I wonder how others handle the following case:

Answer 1

    public MyItem SelectedItem { get; set; }
    private MyItem selectedItem ;
    // 

    ///////
    // 
    public MyItem SelectedItem 
    {
        get { return selectedItem ; }
        set
        {
            if (value != null && selectedItem != value)
            {
                selectedItem = value;
                if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs("SelectedItem ")); }
            }
        }
    }