Xamarin Wrong Count of NavigationStack in OnAppearing after Navigatig Back

user_5203853 0
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I am using the following method to set the pagenumber of my current page:

protected override void OnAppearing()
{
    base.OnAppearing();
    // Page number
    _pageNumber = Navigation.NavigationStack.Count - 2;
}

Everything works fine, if I am navigating forward and pushing a new page onto the stack like this:

private async void btnContinue_Clicked(object sender, EventArgs e)
{
    // Proceed to next view
    await Navigation.PushAsync(new MainPage());
}

However, when I am navigating back from one page, the OnAppearing() method seems to be called before the previous page is popped. Thus, the _pageNumber variable will effectively be the one of the previous page. How do I work around that? I thought of placing it inside the constructor but the NavigationStack.Count always returns 0 in there. My pages are dynamically programmed, therefore, I cannot hardcode the page number into the page because the same page is called but the values are changing based on the number of the page.

xamarin.forms xamarin
1 Answers

This will be an expected effect .

When the PopAsync method is invoked, the following events occur:

  1. The page calling PopAsync has its OnDisappearing override invoked.
  2. The page being returned to has its OnAppearing override invoked.
  3. The PopAsync task returns.

So if you want to get current count of NavigationStack , you could improve the answer like following :

In the demo , I used MessageingCenter to pass the current of NavigationStack to last page . And the label will display the current NavigationStack .

bool isFirstLoad = true;

protected override void OnAppearing()
{
    base.OnAppearing();

    if(isFirstLoad)
    {
      label.Text = Navigation.NavigationStack.Count.ToString();
      isFirstLoad = false;
    }

    MessagingCenter.Subscribe<Object,int>(this, "pop", (arg, num) => {

      label.Text = (num-1).ToString();

     });

}

And when you call Pop 

 private async void Button_Clicked_1(object sender, EventArgs e)
{
   MessagingCenter.Send<Object,int>(this, "pop", Navigation.NavigationStack.Count);
   await Navigation.PopAsync();
}

enter image description here

user_102169820
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