Shell/Flyout Navigation Bar - Back Button Pressed - want to intercept in ViewModels c# file

Question

Hi

I am using Visual Studio 2022/xamarin/C# to develop my App.

I am trying to resolve an issue where I want to intercept the pressing of the Back Button on the Shell Navigation Bar, for one of my pages, so I can execute some c# code in my ViewModel.

I know you can use the OnDisappearing() module in the View Page, but I want to use it in the ViewModel code behind.

Have look at various solutions, but they don't work.

Also does the page/data get cleared from memory when back button is pressed?

Thanks

Answer 1

Hello,

You can bind a Command to Back Button in Shell, then execute some c# code in your ViewModel's command event.

For example, I have a detailed page, I add Shell.BackButtonBehavior and bind a BackButtonCommand

   <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"  
                xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"  
                x:Class="App2.Views.ItemDetailPage"  
                Title="{Binding Title}">  
       <Shell.BackButtonBehavior>  
           <BackButtonBehavior Command="{Binding BackButtonCommand}"/>  
       </Shell.BackButtonBehavior>  

We can execute some C# code in the ViewModel when click the back button.

   public ICommand BackButtonCommand { get; set; }  
     
          public ItemDetailViewModel()  
           {  
               BackButtonCommand = new Command(async () => {  
                   //Execute your code when click the back button in the shell  
                   
     
                  //navigate to the previous page  
                 await  Shell.Current.GoToAsync("..");  
               });  
           }  

Best Regards,

Leon Lu

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