Close Window from ViewModel

Im creating a Login using a window control to allow a user to login into a WPF application that I am creating.

So far, I have created a method that checks whether the user has entered in the correct credentials for the username and password in a textbox on the login screen, binding two properties.

I have achieved this by creating a bool method, like so;

public bool CheckLogin()
{
    var user = context.Users.Where(i => i.Username == this.Username).SingleOrDefault();

    if (user == null)
    {
        MessageBox.Show("Unable to Login, incorrect credentials.");
        return false;
    }
    else if (this.Username == user.Username || this.Password.ToString() == user.Password)
    {
        MessageBox.Show("Welcome " + user.Username + ", you have successfully logged in.");

        return true;
    }
    else
    {
        MessageBox.Show("Unable to Login, incorrect credentials.");
        return false;
    }
}

public ICommand ShowLoginCommand
{
    get
    {
        if (this.showLoginCommand == null)
        {
            this.showLoginCommand = new RelayCommand(this.LoginExecute, null);
        }
        return this.showLoginCommand;
    }
}

private void LoginExecute()
{
    this.CheckLogin();
} 

I also have a command that I bind to my button within the xaml like so;

<Button Name="btnLogin" IsDefault="True" Content="Login" Command="{Binding ShowLoginCommand}" />

When I enter in the username and password it executes the appropriated code, whether it being right, or wrong. But how can I close this window from the ViewModel when both username and password are correct?

I have previously tried using a dialog modal but it didn't quite work out. Furthermore, within my app.xaml, I have done something like the following, which loads the login page first, then once true, loads the actual application.

private void ApplicationStart(object sender, StartupEventArgs e)
{
    Current.ShutdownMode = ShutdownMode.OnExplicitShutdown;

    var dialog = new UserView();

    if (dialog.ShowDialog() == true)
    {
        var mainWindow = new MainWindow();
        Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
        Current.MainWindow = mainWindow;
        mainWindow.Show();
    }
    else
    {
        MessageBox.Show("Unable to load application.", "Error", MessageBoxButton.OK);
        Current.Shutdown(-1);
    }
}

Question: How can I close the Login Window control from the ViewModel?

Thanks in advance.

You can pass the window to your ViewModel using the CommandParameter. See my Example below.

I've implemented an CloseWindow Method which takes a Windows as parameter and closes it. The window is passed to the ViewModel via CommandParameter. Note that you need to define an x:Name for the window which should be close. In my XAML Window i call this method via Command and pass the window itself as a parameter to the ViewModel using CommandParameter.

Command="{Binding CloseWindowCommand, Mode=OneWay}" 
CommandParameter="{Binding ElementName=TestWindow}"

ViewModel

public RelayCommand<Window> CloseWindowCommand { get; private set; }

public MainViewModel()
{
    this.CloseWindowCommand = new RelayCommand<Window>(this.CloseWindow);
}

private void CloseWindow(Window window)
{
    if (window != null)
    {
       window.Close();
    }
}

View

<Window x:Class="ClientLibTestTool.ErrorView"
        x:Name="TestWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:localization="clr-namespace:ClientLibTestTool.ViewLanguages"
        DataContext="{Binding Main, Source={StaticResource Locator}}"
        Title="{x:Static localization:localization.HeaderErrorView}"
        Height="600" Width="800"
        ResizeMode="NoResize"
        WindowStartupLocation="CenterScreen">
    <Grid> 
        <Button Content="{x:Static localization:localization.ButtonClose}" 
                Height="30" 
                Width="100" 
                Margin="0,0,10,10" 
                IsCancel="True" 
                VerticalAlignment="Bottom" 
                HorizontalAlignment="Right" 
                Command="{Binding CloseWindowCommand, Mode=OneWay}" 
                CommandParameter="{Binding ElementName=TestWindow}"/>
    </Grid>
</Window>

Note that i'm using the MVVM light framework, but the principal applies to every wpf application.

This solution violates of the MVVM pattern, because the view-model shouldn't know anything about the UI Implementation. If you want to strictly follow the MVVM programming paradigm you have to abstract the type of the view with an interface.

MVVM conform solution (Former EDIT2)

the user Crono mentions a valid point in the comment section: > Passing the Window object to the view model breaks the MVVM pattern > IMHO, because it forces your vm to know what it's being viewed in.

You can fix this by introducing an interface containing a close method.

Interface:

public interface ICloseable
{
    void Close();
}

Your refactored ViewModel will look like this:

ViewModel

public RelayCommand<ICloseable> CloseWindowCommand { get; private set; }

public MainViewModel()
{
    this.CloseWindowCommand = new RelayCommand<IClosable>(this.CloseWindow);
}

private void CloseWindow(ICloseable window)
{
    if (window != null)
    {
        window.Close();
    }
}

You have to reference and implement the ICloseable interface in your view

View (Code behind)

public partial class MainWindow : Window, ICloseable
{
    public MainWindow()
    {
        InitializeComponent();
    }
}

Answer to the original question: (former EDIT1)

Your Login Button (Added CommandParameter):

<Button Name="btnLogin" IsDefault="True" Content="Login" Command="{Binding ShowLoginCommand}" CommandParameter="{Binding ElementName=LoginWindow}"/>

Your code:

 public RelayCommand<Window> CloseWindowCommand { get; private set; } // the <Window> is important for your solution!

 public MainViewModel() 
 {
     //initialize the CloseWindowCommand. Again, mind the <Window>
     //you don't have to do this in your constructor but it is good practice, thought
     this.CloseWindowCommand = new RelayCommand<Window>(this.CloseWindow);
 }

 public bool CheckLogin(Window loginWindow) //Added loginWindow Parameter
 {
    var user = context.Users.Where(i => i.Username == this.Username).SingleOrDefault();

    if (user == null)
    {
        MessageBox.Show("Unable to Login, incorrect credentials.");
        return false;
    }
    else if (this.Username == user.Username || this.Password.ToString() == user.Password)
    {
        MessageBox.Show("Welcome "+ user.Username + ", you have successfully logged in.");
        this.CloseWindow(loginWindow); //Added call to CloseWindow Method
        return true;
    }
    else
    {
        MessageBox.Show("Unable to Login, incorrect credentials.");
        return false;
    }
 }
 
 //Added CloseWindow Method
 private void CloseWindow(Window window)
 {
     if (window != null)
     {
         window.Close();
     }
 }

I usually put an event on the view model when I need to do this and then hook it up to the Window.Close() when binding the view model to the window

public class LoginViewModel
{
    public event EventHandler OnRequestClose;

    private void Login()
    {
        // Login logic here
        OnRequestClose(this, new EventArgs());
    }
}

And when creating the login window

var vm = new LoginViewModel();
var loginWindow = new LoginWindow
{
    DataContext = vm
};
vm.OnRequestClose += (s, e) => loginWindow.Close();

loginWindow.ShowDialog(); 

Staying MVVM, I think using either Behaviors from the Blend SDK (System.Windows.Interactivity) or a custom interaction request from Prism could work really well for this sort of situation.

If going the Behavior route, here's the general idea:

public class CloseWindowBehavior : Behavior<Window>
{
    public bool CloseTrigger
    {
        get { return (bool)GetValue(CloseTriggerProperty); }
        set { SetValue(CloseTriggerProperty, value); }
    }

    public static readonly DependencyProperty CloseTriggerProperty =
        DependencyProperty.Register("CloseTrigger", typeof(bool), typeof(CloseWindowBehavior), new PropertyMetadata(false, OnCloseTriggerChanged));

    private static void OnCloseTriggerChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var behavior = d as CloseWindowBehavior;

        if (behavior != null)
        {
            behavior.OnCloseTriggerChanged();
        }
    }

    private void OnCloseTriggerChanged()
    {
        // when closetrigger is true, close the window
        if (this.CloseTrigger)
        {
            this.AssociatedObject.Close();
        }
    }
}

Then in your window, you would just bind the CloseTrigger to a boolean value that would be set when you wanted the window to close.

<Window x:Class="TestApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        xmlns:local="clr-namespace:TestApp"
        Title="MainWindow" Height="350" Width="525">
    <i:Interaction.Behaviors>
        <local:CloseWindowBehavior CloseTrigger="{Binding CloseTrigger}" />
    </i:Interaction.Behaviors>
    
    <Grid>
        
    </Grid>
</Window>

Finally, your DataContext/ViewModel would have a property that you'd set when you wanted the window to close like this:

public class MainWindowViewModel : INotifyPropertyChanged
{
    private bool closeTrigger;

    /// <summary>
    /// Gets or Sets if the main window should be closed
    /// </summary>
    public bool CloseTrigger
    {
        get { return this.closeTrigger; }
        set
        {
            this.closeTrigger = value;
            RaisePropertyChanged(nameof(CloseTrigger));
        }
    }

    public MainWindowViewModel()
    {
        // just setting for example, close the window
        CloseTrigger = true;
    }

    protected void RaisePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

(set your Window.DataContext = new MainWindowViewModel())

it may be late, but here is my answer

foreach (Window item in Application.Current.Windows)
{
    if (item.DataContext == this) item.Close();
}

Well here is something I used in several projects. It may look like a hack, but it works fine.

public class AttachedProperties : DependencyObject //adds a bindable DialogResult to window
{
    public static readonly DependencyProperty DialogResultProperty = 
        DependencyProperty.RegisterAttached("DialogResult", typeof(bool?), typeof(AttachedProperties), 
        new PropertyMetaData(default(bool?), OnDialogResultChanged));

    public bool? DialogResult
    {
        get { return (bool?)GetValue(DialogResultProperty); }
        set { SetValue(DialogResultProperty, value); }
    }

    private static void OnDialogResultChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var window = d as Window;
        if (window == null)
            return;

        window.DialogResult = (bool?)e.NewValue;
    }
}

Now you can bind DialogResult to a VM and set its value of a property. The Window will close, when the value is set.

<!-- Assuming that the VM is bound to the DataContext and the bound VM has a property DialogResult -->
<Window someNs:AttachedProperties.DialogResult={Binding DialogResult} />

This is an abstract of what's running in our production environment

<Window x:Class="AC.Frontend.Controls.DialogControl.Dialog"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:DialogControl="clr-namespace:AC.Frontend.Controls.DialogControl"
xmlns:hlp="clr-namespace:AC.Frontend.Helper"
MinHeight="150" MinWidth="300" ResizeMode="NoResize" SizeToContent="WidthAndHeight"
WindowStartupLocation="CenterScreen" Title="{Binding Title}"
hlp:AttachedProperties.DialogResult="{Binding DialogResult}" WindowStyle="ToolWindow" ShowInTaskbar="True"
Language="{Binding UiCulture, Source={StaticResource Strings}}">
<!-- A lot more stuff here -->
</Window>

As you can see, I'm declaring the namespace xmlns:hlp="clr-namespace:AC.Frontend.Helper" first and afterwards the binding hlp:AttachedProperties.DialogResult="{Binding DialogResult}".

The AttachedProperty looks like this. It's not the same I posted yesterday, but IMHO it shouldn't have any effect.

public class AttachedProperties
{
#region DialogResult



public static readonly DependencyProperty DialogResultProperty =
    DependencyProperty.RegisterAttached("DialogResult", typeof (bool?), typeof (AttachedProperties), new PropertyMetadata(default(bool?), OnDialogResultChanged));

private static void OnDialogResultChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var wnd = d as Window;
    if (wnd == null)
        return;

    wnd.DialogResult = (bool?) e.NewValue;
}

public static bool? GetDialogResult(DependencyObject dp)
{
    if (dp == null) throw new ArgumentNullException("dp");

    return (bool?)dp.GetValue(DialogResultProperty);
}

public static void SetDialogResult(DependencyObject dp, object value)
{
    if (dp == null) throw new ArgumentNullException("dp");

    dp.SetValue(DialogResultProperty, value);
}

#endregion




}
}

Easy way

public interface IRequireViewIdentification
{
    Guid ViewID { get; }
}

Implement to ViewModel

public class MyViewVM : IRequireViewIdentification
{
    private Guid _viewId;

    public Guid ViewID
    {
        get { return _viewId; }
    }

    public MyViewVM()
    {
        _viewId = Guid.NewGuid();
    }
}

Add general window manager helper

public static class WindowManager
{
    public static void CloseWindow(Guid id)
    {
        foreach (Window window in Application.Current.Windows)
        {
            var w_id = window.DataContext as IRequireViewIdentification;
            if (w_id != null && w_id.ViewID.Equals(id))
            {
                window.Close();
            }
        }
    }
}

And close it like this in viewmodel

WindowManager.CloseWindow(ViewID);

I know this is an old post, probably no one would scroll this far, I know I didn't. So, after hours of trying different stuff, I found this blog and dude killed it. Simplest way to do this, tried it and it works like a charm.

Blog

In the ViewModel:

...

public bool CanClose { get; set; }

private RelayCommand closeCommand;
public ICommand CloseCommand
{
    get
    {
        if(closeCommand == null)
        (
            closeCommand = new RelayCommand(param => Close(), param => CanClose);
        )
    }
}

public void Close()
{
    this.Close();
}

...

add an Action property to the ViewModel, but define it from the View’s code-behind file. This will let us dynamically define a reference on the ViewModel that points to the View.

On the ViewModel, we’ll simply add:

public Action CloseAction { get; set; }

And on the View, we’ll define it as such:

public View()
{
    InitializeComponent() // this draws the View
    ViewModel vm = new ViewModel(); // this creates an instance of the ViewModel
    this.DataContext = vm; // this sets the newly created ViewModel as the DataContext for the View
    if ( vm.CloseAction == null )
        vm.CloseAction = new Action(() => this.Close());
}

Here is a simple example using the MVVM Light Messenger instead of an event. The view model sends a close message when a button is clicked:

    public MainViewModel()
    {
        QuitCommand = new RelayCommand(ExecuteQuitCommand);
    }

    public RelayCommand QuitCommand { get; private set; }

    private void ExecuteQuitCommand() 
    {
        Messenger.Default.Send<CloseMessage>(new CloseMessage());
    }

Then it is received in the code behind of the window.

    public Main()
    {   
        InitializeComponent();
        Messenger.Default.Register<CloseMessage>(this, HandleCloseMessage);
    }

    private void HandleCloseMessage(CloseMessage closeMessage)
    {
        Close();
    }

How about this ?

ViewModel:

class ViewModel
{
    public Action CloseAction { get; set; }
    private void Stuff()
    {
       // Do Stuff
       CloseAction(); // closes the window
    }
}

In your ViewModel use CloseAction() to close the window just like in the example above.

View:

public View()
{
    InitializeComponent();
    ViewModel vm = new ViewModel (); // this creates an instance of the ViewModel
    this.DataContext = vm; // this sets the newly created ViewModel as the DataContext for the View
    if (vm.CloseAction == null)
        vm.CloseAction = new Action(() => this.Close());
}

You can create new Event handler in the ViewModel like this.

public event EventHandler RequestClose;

    protected void OnRequestClose()
    {
        if (RequestClose != null)
            RequestClose(this, EventArgs.Empty);
    }

Then Define RelayCommand for ExitCommand.

private RelayCommand _CloseCommand;
    public ICommand CloseCommand
    {
        get
        {
            if(this._CloseCommand==null)
                this._CloseCommand=new RelayCommand(CloseClick);
            return this._CloseCommand;
        }
    }

    private void CloseClick(object obj)
    {
        OnRequestClose();
    }

Then In XAML file set

<Button Command="{Binding CloseCommand}" />

Set the DataContext in the xaml.cs File and Subscribe to the event we created.

public partial class MainWindow : Window
{
    private ViewModel mainViewModel = null;
    public MainWindow()
    {
        InitializeComponent();
        mainViewModel = new ViewModel();
        this.DataContext = mainViewModel;
        mainViewModel.RequestClose += delegate(object sender, EventArgs args) { this.Close(); };
    }
}

My proffered way is Declare event in ViewModel and use blend InvokeMethodAction as below.

Sample ViewModel

public class MainWindowViewModel : BindableBase, ICloseable
{
    public DelegateCommand SomeCommand { get; private set; }
    #region ICloseable Implementation
    public event EventHandler CloseRequested;        

    public void RaiseCloseNotification()
    {
        var handler = CloseRequested;
        if (handler != null)
        {
            handler.Invoke(this, EventArgs.Empty);
        }
    }
    #endregion

    public MainWindowViewModel()
    {
        SomeCommand = new DelegateCommand(() =>
        {
            //when you decide to close window
            RaiseCloseNotification();
        });
    }
}

I Closeable interface is as below but don't require to perform this action. ICloseable will help in creating generic view service, so if you construct view and ViewModel by dependency injection then what you can do is

internal interface ICloseable
{
    event EventHandler CloseRequested;
}

Use of ICloseable

var viewModel = new MainWindowViewModel();
        // As service is generic and don't know whether it can request close event
        var window = new Window() { Content = new MainView() };
        var closeable = viewModel as ICloseable;
        if (closeable != null)
        {
            closeable.CloseRequested += (s, e) => window.Close();
        }

And Below is Xaml, You can use this xaml even if you don't implement interface, it will only need your view model to raise CloseRquested.

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WPFRx"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions" 
xmlns:ViewModels="clr-namespace:WPFRx.ViewModels" x:Name="window" x:Class="WPFRx.MainWindow"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525" 
d:DataContext="{d:DesignInstance {x:Type ViewModels:MainWindowViewModel}}">

<i:Interaction.Triggers>
    <i:EventTrigger SourceObject="{Binding Mode=OneWay}" EventName="CloseRequested" >
        <ei:CallMethodAction TargetObject="{Binding ElementName=window}" MethodName="Close"/>
    </i:EventTrigger>
</i:Interaction.Triggers>

<Grid>
    <Button Content="Some Content" Command="{Binding SomeCommand}" Width="100" Height="25"/>
</Grid>

You can use Messenger from MVVMLight toolkit. in your ViewModel send a message like this:
Messenger.Default.Send(new NotificationMessage("Close"));
then in your windows code behind, after InitializeComponent, register for that message like this:

Messenger.Default.Register<NotificationMessage>(this, m=>{
    if(m.Notification == "Close") 
    {
        this.Close();
    }
   });

you can find more about MVVMLight toolkit here: MVVMLight toolkit on Codeplex

Notice that there is not a "no code-behind at all rule" in MVVM and you can do registering for messages in a view code-behind.

It's simple. You can create your own ViewModel class for Login - LoginViewModel. You can create view var dialog = new UserView(); inside your LoginViewModel. And you can set-up Command LoginCommand into button.

<Button Name="btnLogin" IsDefault="True" Content="Login" Command="{Binding LoginCommand}" />

and

<Button Name="btnCancel" IsDefault="True" Content="Login" Command="{Binding CancelCommand}" />

ViewModel class:

public class LoginViewModel
{
    Window dialog;
    public bool ShowLogin()
    {
       dialog = new UserView();
       dialog.DataContext = this; // set up ViewModel into View
       if (dialog.ShowDialog() == true)
       {
         return true;
       }

       return false;
    }

	ICommand _loginCommand
	public ICommand LoginCommand
	{
		get
		{
			if (_loginCommand == null)
				_loginCommand = new RelayCommand(param => this.Login());

			return _loginCommand;
		}
	}
   
    public void CloseLoginView()
	{
            if (dialog != null)
		  dialog.Close();
	}	
   
	public void Login()
	{
		if(CheckLogin()==true)
		{
			CloseLoginView();         
		}
		else
		{
		  // write error message
		}
	}

    public bool CheckLogin()
    {
      // ... check login code
      return true;
    }
}

This is a way I did it pretty simply:

YourWindow.xaml.cs

//In your constructor
public YourWindow()
{
    InitializeComponent();
    DataContext = new YourWindowViewModel(this);
}

YourWindowViewModel.cs

private YourWindow window;//so we can kill the window

//In your constructor
public YourWindowViewModel(YourWindow window)
{
    this.window = window;
}

//to close the window
public void CloseWindow()
{
    window.Close();
}

I don't see anything wrong with the answer you chose, I just thought this might be a more simple way to do it!

You may treat window as a service (eg. UI service) and pass itself to viewmodel via an interface, as such:

public interface IMainWindowAccess
{
    void Close(bool result);
}

public class MainWindow : IMainWindowAccess
{
    // (...)
    public void Close(bool result)
    {
        DialogResult = result;
        Close();
    }
}

public class MainWindowViewModel
{
    private IMainWindowAccess access;

    public MainWindowViewModel(IMainWindowAccess access)
    {
        this.access = access;
    }

    public void DoClose()
    {
        access.Close(true);
    }
}

This solution have most upsides of passing the view itself to viewmodel without having downside of breaking MVVM, because though physically view is passed to viewmodel, the latter still don't know about the former, it sees only some IMainWindowAccess. So for instance if we wanted to migrate this solution to other platform, it would be only a matter of implementing IMainWindowAccess properly for, say, an Activity.

I'm posting the solution here to propose a different approach than events (though it's actually very similar), because it seems a little bit simpler than events to implement (attaching/detaching etc.), but still aligns nicely with MVVM pattern.

In MVVM WPF I usually design my View as a UserControl. And It is just a matter of how you want to display It. If you want It to be in a Window, then you could do a WindowService class:

public class WindowService
{
   //...

   public void Show_window(object viewModel, int height, int width, string title)
   {
     var window = new Window
     {
       Content = viewModel,
       Title = title,
       Height = height,
       Width = width,
       WindowStartupLocation = WindowStartupLocation.CenterOwner,
       Owner = Application.Current.MainWindow,
       Style = (Style)Application.Current.FindResource("Window_style") //even style can be added
      };

      //If you own custom window style, then you can bind close/minimize/maxmize/restore buttons like this 
      window.CommandBindings.Add(new CommandBinding(SystemCommands.CloseWindowCommand, OnCloseWindow));
      window.CommandBindings.Add(new CommandBinding(SystemCommands.MaximizeWindowCommand, OnMaximizeWindow, OnCanResizeWindow));
      window.CommandBindings.Add(new CommandBinding(SystemCommands.MinimizeWindowCommand, OnMinimizeWindow, OnCanMinimizeWindow));
      window.CommandBindings.Add(new CommandBinding(SystemCommands.RestoreWindowCommand, OnRestoreWindow, OnCanResizeWindow));
                  
      window.ShowDialog();
   }

   public void Close_window(object viewmodel)
   {
       //Close window
       foreach (Window item in Application.Current.Windows)
       {
          if (item.Content == viewmodel) item.Close();
       }
    }
}

Using my approach is simple. Usually you want to close Window when something happens in It. So, when It does, just call Close_window method from corresponding ViewModel - the one which is DataContext of UserControl which is displayed in a Window. Look bottom example:

1.) We open Window from some Viewmodel:

public class MyViewModel // ViewModel where you open window
{
   private readonly WindowService _windowservice // or inject/inherit from Base

   public MyViewModel()
   {
     _windowservice = new WindowService();
   }  

   private void Example_method()
   {
        //...Open window
        _windowservice.Show_window(new WindowViewModel(),100,100,"Test window");
   }
  
}

2.) Our Window is allready opened, now we want to close It :

 public class WindowViewModel // ViewModel which is your Window content!
 {
     private readonly WindowService _windowservice // or inject/inherit from Base

     public MyViewModel()
     {
       _windowservice = new WindowService();
     }  

     private void Example_method()
     {
          //Close window
          _windowservice.Close(this); //Pass a reference of viewmodel to method
     }
    
  }

This solution is far less elegant that other accepted answers, but for me It works. I use It widely in projects, so far no problems with It. But I'm sure that someone will come and say "That is a violation of MVVM principle".

You can close the current window just by using the following code:

Application.Current.Windows[0].Close();

System.Environment.Exit(0); in view model would work.