How to pushasync from detailpage in masterdetailpage? - ios

Question

From the detailpage's view I try to push a new page on and I get this error: **
System.InvalidOperationException: Page must not already have a parent.
I keep trying different things but nothing works. Is there a way to push a page onto it, I mean, the detailpage is a navigationpage but it is a detailpage. Any and all help is much appreciated.
I am using xamarin forms labs ViewFactory.
//app.cs GetMainPage
var rootPage = ViewFactory.CreatePage<HomeVM>();
//in HomeView.xaml.cs, setting the detailpage to the list of messages
Detail = new NavigationPage(ViewFactory.CreatePage<MessagesVM>());
//This is in the MessagesView to show an individual message with a back button to the list of messages
Navigation.PushAsync(ViewFactory.CreatePage<MessageDetailVM>());

Answer 1

If you already have a NavigationPage, do not create another one to wrap your Detail instance in.
Detail = iewFactory.CreatePage<MessagesVM>();
Navigation.PushAsync(ViewFactory.CreatePage<MessageDetailVM>());

Answer 2

On my part, I also having the same error using MessagingCenter, but also solve it by unsubscribing/disposing after page closing/OnDisappearing.
Hope it helps.
public partial class MainPage : MasterDetailPage
{
public MainPage()
{
InitializeComponent();
MasterBehavior = MasterBehavior.Popover;
MessagingCenter.Subscribe<NavigationPage>(this, "Navigate", (pageItem) =>
{
Detail = pageItem;
IsPresented = false;
});
MessagingCenter.Subscribe<string>(this, "Logout", (s) =>
{
Application.Current.MainPage = new LoginPage("", "");
});
}
protected override void OnDisappearing()
{
MessagingCenter.Unsubscribe<NavigationPage>(this, "Navigate");
MessagingCenter.Unsubscribe<string>(this, "Logout");
base.OnDisappearing();
}
}
Unfortunately, I encountered this error again, and I solve it by using this setting the NavigationPage Parent property to null.
MessagingCenter.Subscribe<NavigationPage>(this, "Navigate", (pageItem) =>
{
pageItem.Parent = null; //solution
Detail = pageItem;
IsPresented = false;
});

Answer 3

Both answers before mine are pointing to the right direction, so this is just an addition. The key is in fact to not create the NavigationPage/NavigationView again.
In my project, I am using static objects for the MasterDetailPage, the NavigationView and the corresponding ViewModels in Xamarin Forms App class;
I am only creating an instance if their Value is null, which is likely to happen only if the app was closed before (no matter if closed by the user or the OS). If the app is still running (resumed), I am just using the already existing objects to restore the state.
This solved all these problems for me, and I hope it is helpful for someone else.

Answer 4

Try using the Navigation property of the Detail object like this:
Detail.Navigation.PushAsync(page);
To push a new page on my Detail I use the code below:
Note there I'm using a ListView with page options in MasterDetailPage
private void ListView_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
var item = e.SelectedItem as MainMenuItem;
if (item == null)
return;
var page = (Page)Activator.CreateInstance(item.TargetType);
//Detail = new NavigationPage(page);
Detail.Navigation.PushAsync(page);
IsPresented = false;
MasterPage.ListView.SelectedItem = null;
}