Cancel combobox selection in WPF with MVVM

Question

I\'ve got a combobox in my WPF application:

Answer 1

I think the problem is that the ComboBox sets the selected item as a result of the user action after setting the bound property value. Thus the Combobox item changes no matter what you do in the ViewModel. I found a different approach where you don't have to bend the MVVM pattern. Here's my example (sorry that it is copied from my project and does not exactly match the examples above):

public ObservableCollection Styles { get; }

public StyleModelBase SelectedStyle {
  get { return selectedStyle; }
  set {
    if (value is CustomStyleModel) {
      var buffer = SelectedStyle;
      var items = Styles.ToList();
      if (openFileDialog.ShowDialog() == true) {
        value.FileName = openFileDialog.FileName;
      }
      else {
        Styles.Clear();
        items.ForEach(x => Styles.Add(x));
        SelectedStyle = buffer;
        return;
      }
    }
    selectedStyle = value;
    OnPropertyChanged(() => SelectedStyle);
  }
}

The difference is that I completely clear the items collection and then fill it with the items stored before. This forces the Combobox to update as I'm using the ObservableCollection generic class. Then I set the selected item back to the selected item that was set previously. This is not recommended for a lot of items because clearing and filling the combobox is kind of expensive.