Q:

when i am using xamarin MVVM.  so how to handle Device Back(Hardware back button) in view model

I am creating one app in xamarin cross platform with MVVM, I want to handle device back navigation so how can i handle it?  please help me. 
Thanks in advance

A:

Well, that's quite simple actually just add a command in your VM and call that command from your View when you need to handle this event! 
In your View
protected override bool OnBackButtonPressed()
{
   var vm = (ViewModel)BindingContext;
   if(vm. MyBackPressCommand. CanExecute())  // You can add parameters if any
     {
         MyBackPressCommand. Execute(); // You can add parameters if any
     }
}

Also, define this in your ViewModel
public ICommand MyBackPressCommand { get; set; }

And also this needs to be initialized(constructor) like below:
MyBackPressCommand= new Xamarin. Forms. Command(()=>{});

You can use inheritance to make this globally available for all derived versions of your View/ViewModel

