Question

Ok, so what I am looking to do is to display some sort of login control (maybe a UserControl with a TextBox and PasswordBox) when the app is started.

In a non-mvvm situation, a way of doing this would be to use the PopUp primitive control, add the usercontrol as a child element and off you go.

In an MVVM situation, i’m a bit confused about how you would achieve a simmilar result.

I have looked into messaging with the DialogMessage and this is fine for displaying a typical MessageBox, but what about a custom usercontrol?

any help would be fantastic! I can’t seem to find any demo code of this anywhere.

Answer 1

In a MVVM situation you can use a delegate to let your View open the dialog when the ViewModel requests it.

You define a delegate at the VM:

public Func<LoginResult> ShowLoginDialogDelegate;

In your View you define the function that will be called:

private LoginResult ShowLoginDialog()
{
    LoginResult result;
    // show a dialog and get the login data
    return result;
}

Then you “connect” the delegate and method in the View:

_viewModel = new MyViewModel();
DataContext = _viewModel;
_viewModel.ShowLoginDialogDelegate += ShowLoginDialog;

And now you can use it in your ViewModel e.g. when a command is executed like that:

LoginResult result = ShowLoginDialogDelegate();