Handling the window closing event with WPF / MVVM Light Toolkit
I'd like to handle the "Closing" event (when a user clicks the upper right 'X' button) of my window in order to eventually display a confirm message or/and cancel the closing.
I know how to do this in the code-behind : subscribe to the "Closing" event of the window then use the "CancelEventArgs.Cancel" property.
But I'm using MVVM so I'm not sure it's the good approach.
I think the good approach would be to bind the Closing event to a Command in my ViewModel.
I tried that :
<i:Interaction.Triggers>
<i:EventTrigger EventName="Closing">
<cmd:EventToCommand Command="{Binding CloseCommand}" />
</i:EventTrigger>
</i:Interaction.Triggers>
With an associated RelayCommand in my ViewModel but it doesn't work (the command's code is not executed).
I would simply associate the handler in the View constructor:
MyWindow()
{
// Set up ViewModel, assign to DataContext etc.
Closing += viewModel.OnWindowClosing;
}
Then add the handler to the ViewModel :
public void OnWindowClosing(object sender, CancelEventArgs e)
{
// Handle closing logic, set e.Cancel as needed
}
In this case, you gain exactly nothing except complexity by using a more elaborate pattern with more indirection (5 extra lines of XML plus command pattern).
The "zero code-behind" mantra is not the goal in itself, the point is to decouple ViewModel from the View . Even when the event is bound in code-behind of the View, the ViewModel does not depend on the View and the closing logic can be unit-tested .
This code works just fine:
ViewModel.cs:
public ICommand WindowClosing
{
get
{
return new RelayCommand<CancelEventArgs>(
(args) =>{
});
}
}
and in XAML:
<i:Interaction.Triggers>
<i:EventTrigger EventName="Closing">
<command:EventToCommand Command="{Binding WindowClosing}" PassEventArgsToCommand="True" />
</i:EventTrigger>
</i:Interaction.Triggers>
and, of course, the ViewModel is assigned to a DataContext of main container.
This option is even easier, and maybe is suitable for you. In your View Model constructor, you can subscribe the Main Window closing event like this:
Application.Current.MainWindow.Closing += new CancelEventHandler(MainWindow_Closing);
void MainWindow_Closing(object sender, CancelEventArgs e)
{
//Your code to handle the event
}
All the best.
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