WPF ComboBox SelectedItem - change to previous value

Question

I have a ComboBox that has the SelectedItem bound to the ViewModel.

Answer 1

My way of doing it is to let the change go through and perform validation in a lambda that is BeginInvoked in the Dispatcher.

    public ObservableCollection Items { get; set; }
    private string _selectedItem;
    private string _oldSelectedItem;
    public string SelectedItem
    {
        get { return _selectedItem; }
        set {
            _oldSelectedItem = _selectedItem;
            _selectedItem = value;
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs("SelectedItem"));
            }
            Dispatcher.BeginInvoke(new Action(Validate));                
        }
    }

    private void Validate()
    {            
        if (SelectedItem == "Item 5")
        {
            if (MessageBox.Show("Keep 5?", "Title", MessageBoxButton.YesNo) == MessageBoxResult.No)
            {
                SelectedItem = _oldSelectedItem;
            }
        }
    }

or in your ViewModel:

   Synchronization.Current.Post(new SendOrPostCallback(Validate), null);