Get hold of the view in the view model

The Problem

Triggered by a tweet from Vaughn Vernon about the question on how to get a reference to the view in a view model I decided to post the solution I used for this.

In general it is not a good practice though, but I needed it sometime as well (mostly because of some part of the system that was not designed with MVVM in mind).

The Solution

I defined an interface for the view and let the view implement it. The interface contains a a reference to the view model through an interface. The view model resides in the views DataContext so we route the property to this:

public interface IView
{ 
  IViewModel ViewModel { get; set; }
}

public partial class View : UserControl, IView
{ 
  public IViewModel ViewModel 
  { 
    get { return DataContext as IViewModel; }
    set { this.DataContext = value; } 
  }
}

The interface for the view model contains a reference to the view through its interface.

public interface IViewModel
{ 
    IView View { get; set; }
}

public class ViewModel : VMBase, IViewModel
{ 
    public IView View { get; set; }
}

Now in the XAML of the view I wire up the view model

<UserControl>
    <UserControl.DataContext>
        <local:ViewModel />
    </UserControl.DataContext>
</UserControl>

In the loaded-event of the view I set the reference back to the view model:

public void Control_Loaded(Object sender, EventArgs e)
{
  if (ViewModel != null)
    ViewModel.View = this;
}

And thats it.

What I like about this solution is that your view / view model know each other only by means of an interface, which gives you a certain amount of decoupling. But it is quite a bit of additional code...

The Drawbacks

As I mentioned earlier it is generally not a good practice to try to do this. Mostly it points to the fact that the system is not MVVMable - but sometimes reality knocks at the door...
A problem with this apporach is timing. If you need the view reference say in the constructor of your view model you wont be successful with the above technique. But you can use it in commands or any time after the view was loaded which was always sufficient for me.
Finally I don't claim that this is a general purpose solution to all cases one might want to use this - it is just what did the job for me.

Maybe it might be helpful to someone else...