Masterdetail Navigation Help

Question

I am not sure if this is set up correct as I am getting null exceptions when page navigation from the masterdetail -"detail" element.

Set is my flow,

App.CS = MainPage = new LoadingView(); loadingview checks if users token is still valid,
if (valid)
2. => Application.Current.MainPage = new FlyoutMenuView(); (THIS IS MY MASTERDETAIL)
else
Application.Current.MainPage = new LoginView();
THEN => Application.Current.MainPage = new FlyoutMenuView();

MASTERDETAIL
Detail = new NavigationPage(new DashboardView()); (Setting the default page in the masterdetail.)

Then I have some simply text buttons to 2x other features for example
private void Folders_OnTapped(object sender, EventArgs e)
{
Detail = new NavigationPage(new FolderSelectorView());
IsPresented = false;
//isPresent will hide the menu
}

My issue is, on these feature pages, "FolderSelectorView" , I have buttons to goto content pages relating to that feature, for example create folder page etc,

I am having to do this:
MasterDetailPage masterDetail = (MasterDetailPage)Application.Current.MainPage; await masterDetail.Detail.Navigation.PushAsync(new CreateFoldersView());

Because Navigation is not working e.g below

await Navigation.PushAsync(new ItemDetailPage());
await Navigation.PushModalAsync(new NavigationPage(new NewItemPage()));

System.NullReferenceException: 'Object reference not set to an instance of an object.'

Have I done something wrong?

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

Here is the related code, you could refer to it.

App.xaml.cs

   public partial class App : Application  
   {  
       public static bool IsLogged { get; set; }  
       public App()  
       {  
           InitializeComponent();  
     
           ...  
           if (IsLogged)  
           {  
               MainPage = new MasterDetailPage1();  
           }  
           else  
           {  
               MainPage = new LoginPage();  
           }  
       }  
   }  

The detail page

   <Button Text="Navigation" Clicked="Button_Clicked"/>  
   ...  
   public partial class TheChildPage : ContentPage  
   {  
       public TheChildPage()  
       {  
           InitializeComponent();  
       }  
       private async void Button_Clicked(object sender, EventArgs e)  
       {  
           MasterDetailPage masterDetail = (MasterDetailPage)Application.Current.MainPage;  
           await masterDetail.Detail.Navigation.PushAsync(new Page1());  
       }  
   }  

Best Regards,

Jarvan Zhang

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