Why can't I access instance properties in the Execute delegate of a DelegateCommand?

Question

I'm used to using lambdas in ways apparently other than this. When I try and define a DelegateCommand , I have to access to non-static members of the enclosing type for the command. Eg:

public ICommand ShowViewCommand { get; set; } = new DelegateCommand<string>(v =>
    {
        var viewModel = new EditFormViewModel;
        var ucType = Assembly.GetExecutingAssembly().GetType(v);
        App.SetWindowView(viewModel, ucType);
    },
v => true);

In the above code, in the App.SetWindowView call, App has a red squiggly underline, and on hovering over it, I am told:

Cannot access non-static property App in static context.

This is not the behaviour I'm used to when using lambdas for closures. What is different here?

Answer 1

You're trying to access an instance member within an auto-implemented property initializer. That's like trying to do so in a field initializer. Basically, you can't reference this even implicitly in initializers, not even within lambda expressions. Instead, you'll need to do that in a constructor:

public ICommand ShowViewCommand { get; set; }

public Foo() // Replace with your class name
{
    ShowViewCommand = v => new DelegateCommand<string>(v =>
    {
        var viewModel = new EditFormViewModel;
        var ucType = Assembly.GetExecutingAssembly().GetType(v);
        App.SetWindowView(viewModel, ucType);
    });
}