Xamarin Forms: Exit prompt is not working when use Navigation.PushAsync for loading a new page.

Question

I am showing a prompt for the exit when a user taps the device back button on the home page.

My code:

private bool AcceptBack;
public static Action EmulateBackPressed;

protected override bool OnBackButtonPressed()
{
    bool value = true;
    var i = this.Children.IndexOf(this.CurrentPage);
    if (i == 0)
    {
        if (AcceptBack)
            return false;
        PromptForExit();
        value = true;
    }
    else
    {
        CurrentPage = Children[0];
        value = true;
    }
    return value;
}

private async void PromptForExit()
{
    if (await DisplayAlert("Confirm to Quit?", "Are you sure you want to quit?", "Yes", "No"))
    {
        AcceptBack = true;
        EmulateBackPressed();
    }
}

On MainActivity:

Pages.CarouselHomePage.EmulateBackPressed = OnBackPressed;

It was working fine when I use the Navigation.PushModalAsync to load new pages. Currently, I am using Navigation.PushAsync for loading new pages; after that, the exit prompt is not showing. When I tap the backbutton it showing the previous page. In my case the homepage is a CarouselPage having 3 children.

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

You need to move the logic of handling navigation to the method OnAppearing .As in the constructor the page has not finished loading yet .

   protected override void OnAppearing()  
           {  
               base.OnAppearing();  
     
               try  
               {  
                   string login = Application.Current.Properties["islogin"].ToString();  
     
                   if (login == "true")  
                   {  
                       Navigation.PushAsync(new CarouselHomePage(), true);  
                   }  
               }  
               catch (Exception e)  
               {  
                   Debug.WriteLine("IsLogin::" + e);  
               }  
           }  

n addition , it should be noted that adding or updating a value in the App.Current.Properties dictionary does not automatically persist it to permanent storage.

So you need to called the method SavePropertiesAsync()

   Application.Current.Properties["islogin"] = "true";  
   Application.Current.SavePropertiesAsync();  

Best Regards,

Leon Lu

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Answer 2

I have created a sample for you
I have removed Navigation because is a problem with Login to have a good Navigation. You could add Navigation to CarouselViewPage if you need to open other pages.

Take a look

https://www.dropbox.com/s/qjbp8zej8fi0ako/MapDemo.rar?dl=0

Answer 3

maybe (but I am not sure) you have to await PromptForExit();

This works for me:

protected override bool OnBackButtonPressed()
    {
        Device.BeginInvokeOnMainThread(async () =>
        {
            var ret = await Application.Current.MainPage.DisplayAlert("Attention", "Close the page?", "Yes", "No");

            if (ret)
                await Application.Current.MainPage.Navigation.PopAsync();
        });
        return true;

        //return base.OnBackButtonPressed();
    }