Implementing "close window" command with MVVM

Question

So my first attempt did everything out of the code behind, and now I'm trying to refactor my code to use the MVVM pattern, following the guidance of the MVVM in the box information.

I've created a viewmodel class to match my view class, and I'm moving the code out of the code behind into the viewmodel starting with the commands.

My first snag is trying to implement a 'Close' button that closes the window if the data has not been modified. I've rigged up a CloseCommand to replace the 'onClick' method and all is good except for where the code tries to run this.Close(). Obviously, since the code has been moved from a window to a normal class, 'this' isn't a window and therefore isn't closeable. However, according to MVVM, the viewmodel doesn't know about the view, so i can't call view.Close().

Can someone suggest how I can close the window from the viewmodel command?

Answer 1

I personally use a very simple approach: for every ViewModel that is related to a closeable View, I created a base ViewModel like this following example:

public abstract class CloseableViewModel
{
    public event EventHandler ClosingRequest;

    protected void OnClosingRequest()
    {
        if (this.ClosingRequest != null)
        {
            this.ClosingRequest(this, EventArgs.Empty);
        }
    }
}

Then in your ViewModel that inherits from CloseableViewModel, simply call this.OnClosingRequest(); for the Close command.

In the view:

public class YourView
{
    ...
    var vm = new ClosableViewModel();
    this.Datacontext = vm;
    vm.ClosingRequest += (sender, e) => this.Close();
}