Access View from current/corresponding ViewModel

Question

Sometimes when developing a WPF application, I need to access a certain Window (View) from the corresponding ViewModel, to perform or fire a method like this for example:

//In the MainWindowViewModel
MainWindowView.Hide(); 

But that's not really easy, and even it violates MVVM because the ViewModel shouldn't know anything about the View, so I started doing this instead:

//In the MainWindowViewModel
Application.Current.MainWindow.Hide();

This becomes impractical when dealing with other Windows (Views):

//In the AnotherWindowView
Application.Current.Windows.OfType<AnotherWindowView>().First().Hide();

So I decided to make a solution, a helper class, in which, using a method, I give the ViewModel and I get back the corresponding View, using the DataContext of the View, the solution looks like this:

The Class:

public static class ViewsAccessibility
{
    public static Window GetCorresponingWindow(ViewModelBase viewModel)
    {
        var windowAccessibility = new WindowAccessibility(viewModel);
        return windowAccessibility.CorrespondanteWindow;
    }

    private class WindowAccessibility 
    {
        public Window CorrespondanteWindow { get; private set; }

        public WindowAccessibility(ViewModelBase viewModel)
        {
            var windows = Application.Current.Windows.OfType<Window>();
            CorrespondanteWindow = (from window in windows
                                      where window.DataContext.Equals(viewModel)
                                      select window).First();
        }
    }
}

The use:

//In the MainWindowViewModel
ViewsAccessibility.GetCorresponingWindow(this).Hide();

Is this a good practice and does it violate MVVM or not?

Answer 1

You have multiple options

a. Use an event Aggregator where publish the message from the viewmodel and subscribe from view. see prism documentation for event aggregators:here is sample code

 //view will subscribe from this message 
_aggregator.GetEvent<CloseEvent>().Subscribe(CloseAction);

 private void CloseAction(string s) { //do your logic }
 //view model will pubilsh this request 
 _aggregator.GetEvent<CloseEvent>().Publish(output);

b. create an interface named as IView and implement it in your view , pass the instance of IView to data context of the view

public partial class Shell : Window ,IView
{
    public Shell()
    {
        InitializeComponent();
        this.DataContext.View = this;
    }

    public void CloseShell()
    {

    }
}

public interface IView
{
    void CloseShell();
}

by using this you have only a reference of interface will be there in viewmodel . but not the whole view itself

Answer 2

what I mostly do when i need to fire an event is this:

I create a Boolean property in my viewmodel and bind this property to the view like this: (Put this in the content of your element)

<Element.Style>
 <Style TargetType="Element">
      <Style.Triggers>
         <DataTrigger Binding="{Binding IsHidden}" Value="True">
            <Setter Property="Visibility" Value="Hidden"/>
         </DataTrigger>
         <DataTrigger Binding="{Binding IsHidden}" Value="False">
            <Setter Property="Visibility" Value="Visible"/>
         </DataTrigger>
      </Style.Triggers>
 </Style>
</Element.Style>

If you want it to be animated you can set the datatrigger.enteractions with a beginstoryboard and in this item your animation. Here are some great examples: http://www.wpf-tutorial.com/styles/trigger-datatrigger-event-trigger/

Also don't forget to put RaisePropertyChanged('NameProperty') in the setter of your property else it won't be triggered when the property is changed at runtime.