6

Suppose I have a ViewModel TabViewModel that Extends ObservableObject the class for ViewModels in the MVVM Foundation Framework. Then I also have a EditorTabViewModel that extends TabViewModel, Now I need to extend DependencyObject to implement DependencyProperties. I cannot extend more than 1 class. How might I implement this? I could have an "intermediate" class like ...

TabViewModel : ObservableObject

EditorTabViewModel : TabViewModel

DependentEditorTabViewModel : DependencyObject

but thats 1 extra unnecessary class. Any better way to do this?

UPDATE

Ops actually I cant do the above. DependentEditorTabViewModel still need to extend EditorTabViewModel ... apart from DependencyObject

Jiew Meng
  • 84,767
  • 185
  • 495
  • 805

2 Answers2

2

C# does not support Multiple Inheritance. Your best bet is to use Interfaces, rather than parent classes.

Even if you don't have the option of using interfaces (maybe you don't have access to the code), it's generally better to prefer composition over inheritance. Do you really need to inherit both of these classes, or can you compose with them instead?

Community
  • 1
  • 1
Matthew
  • 28,056
  • 26
  • 104
  • 170
  • In my above scenario, how could I implement composition over inheritance? I read about that b4 but in this case, maybe my mind is not working well :) – Jiew Meng Oct 17 '10 at 03:47
  • @jiewmeng: I'm afraid I don't know anything about the MVVM Foundation Framework, so I can't help with the details. Sorry. – Matthew Oct 17 '10 at 04:35
1

Its not an extra class if you're accomplishing what you need. Here is how you would go about that:

DependentEditorTabViewModel : DependencyObject

TabViewModel : DependentEditorTabViewModel
Gabriel McAdams
  • 56,921
  • 12
  • 61
  • 77
  • I think I made a similar mistake ... apart from `DependencyObject`, I still need to extend `ObservableObject`. In other words, I need the resultant class to extend mainly `DependencyObject`, `ObservableObject`. – Jiew Meng Oct 17 '10 at 03:34
  • Ok. Unfortunately, c# doesn't support multiple inheritance. Look into implementing an interface instead. – Gabriel McAdams Oct 17 '10 at 03:38