How to manage multiple windows in MVVM

Question

I know that there are several questions like this, but I could not find a definitive answer. I'm trying to dive into MVVM and keep everything as clean as possible, but not sure how to start / close windows, sticking to the template.

My initial thinking was with the commands tied to the ViewModel launch code to launch a new view, with the DataContext, and then set the ViewModel for it via XAML. But this violates pure MVVM, I think ...

After some answers to the search in googling / reading, I came across a concept WindowManager(for example, in CaliburnMicro), now, if I were to implement one of them in the MVVM project with vanilla, is this in my ViewModels? or just at the heart of my application? I am currently separating a project from an assembly / project project Model, assembly / project, ViewModeland assembly / project View. Should this go to another, "sound" assembly?

Which leads a bit to my next question (to some extent related to the above), how do I run the application in terms of MVVM? Initially, I ran my MainView.xaml from App.xaml, and the DataContext in XAML attached the assigned ViewModel. If I add WindowManager, is this the first thing my application launches? Am I doing this from the code behind App.xaml.cs?

Answer 1

Well, basically it depends on how your application looks (that is, how many windows are open at the same time, modal windows or not ... etc.).

The general recommendation that I would give is not to try to make a “clean” MVVM; I often read things like "there must be a ZERO code" ... etc., I do not agree.

Currently, I am separating my project from the assembly / project of the model, ViewModel assembly / project and view assembly / project. If this happens in another, "Core" assembly?

ViewModels - , , -, Model. .

ViewModel , , . , WCF- .

"Core" (IMHO), , , (, ... ..).

( ... ..), , . ViewModels . ViewModels, , , .

, MainWindow, , :

// Main viewModel
public MainViewModel : ViewModelBase
{
    ...
    // EventArgs<T> inherits from EventArgs and contains a EventArgsData property containing the T instance
    public event EventHandler<EventArgs<MyPopupViewModel>> ConfirmationRequested;
    ...
    // Called when ICommand is executed thanks to RelayCommands
    public void DoSomething()
    {
        if (this.ConfirmationRequested != null)
        {
            var vm = new MyPopupViewModel
            {
                // Initializes property of "child" viewmodel depending
                // on the current viewModel state
            };
            this.ConfirmationRequested(this, new EventArgs<MyPopupViewModel>(vm));
        }
    }
}
...
// Main View
public partial class MainWindow : Window
{
    public public MainWindow()
    {
        this.InitializeComponent();

        // Instantiates the viewModel here
        this.ViewModel = new MainViewModel();

        // Attaches event handlers
        this.ViewModel.ConfirmationRequested += (sender, e) =>
        {
            // Shows the child Window here
            // Pass the viewModel in the constructor of the Window
            var myPopup = new PopupWindow(e.EventArgsData);
            myPopup.Show();         
        };
    }

    public MainViewModel ViewModel { get; private set; }
}

// App.xaml, starts MainWindow by setting the StartupUri
<Application x:Class="XXX.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             ...
             StartupUri="Views/MainWindow.xaml">