How to open a modal window the MVVM way

Let's say I have a MainView and a corresponding MainViewModel. The MainView has a button that is supposed to close the window and do some serious stuff before closing (for instance saving data and configurations). This button is bound to a CloseCommand in the MainViewModel, but how do I know in the MainViewModel which view to close. My easy (and wrong) ways would be either to give the MainViewModel an instance of the MainView on initialisation or to give the view-to-close as a command parameter. But both solutions violate the MVVM rule.

Let's say my MainView contains a TextBox bound to a string property of my MainViewModel. If the text, the user types in the TextBox, isn't unique enough, I'd like to open a new modal window in which the user can select his input out of various choices. To open a modal window in WPF you have to put the MainView in the Owner property of the new window. Therefore you need a reference to the MainView in the MainViewModel. Same problem exists, if you try to show a modal message box (a message box that is tied to the parent window and can't be put behind the parent window through mouse clicks or other user actions).

It seems that you wish to close the main window, and that is perfectly fine. As many things, this can be solved with a new level of abstraction. Lets say you have an interface called IApplication with a method Close() . And then lets say you have an implementation of the interface that might look something like:

class ApplicationWrapper : IApplication
{
    public void Close()
    {
        Application.Current.MainWindow.Close();
    }
}

Couldn't you inject the IApplication interface in the view model and call its Close method from the command?

I would propose MVVM Dialogs, but I am biased since I also am the author.