Can't open modal on new main page - xamarin

Question

This code fully demonstrates what looks like a bug. Sequence is...
App opens
Default main page created.
Login box popped up.
Login box closed. (Click on page to simulate)
New main page created.
Login box popped up.(Click on page to simulate)
Exception... Cannot access disposed object.
Any ideas?
using System;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace test333
{
public class Main1 : ContentPage
{
public Main1()
{
var btn = new Button();
btn.Clicked += (sender, e) =>
{
MessagingCenter.Send<object>(this, "LoginLogout");
Navigation.PopModalAsync();
};
Content = btn;
}
}
public partial class App : Application
{
public App()
{
InitializeComponent();
MainPage = new Main1 { BackgroundColor = Color.Red };
MessagingCenter.Subscribe<object>(this, "LoginLogout", s =>
Device.BeginInvokeOnMainThread(async () => await HandleLogOut()));
HandleLogOut();
}
bool login = true;
async Task HandleLogOut()
{
if (login)
{
await MainPage.Navigation.PushModalAsync(new Main1 { BackgroundColor = Color.Orange });
}
else
{
MainPage = new Main1 { BackgroundColor = Color.Green };
}
login = !login;
}
}
}

Answer 1

I think the problem happens in step 6:Login box popped up.(Click on page to simulate).
Have a look at below codes in btn.clicked:
btn.Clicked += (sender, e) =>
{
MessagingCenter.Send<object>(this, "LoginLogout");
Console.WriteLine("popAction");
Navigation.PopModalAsync();
};
And handle logout:
async Task HandleLogOut()
{
if (login)
{
await MainPage.Navigation.PushModalAsync(new Main1 { BackgroundColor = Color.Orange });
Console.WriteLine("PushModalAction");
}
else
{
MainPage = new Main1 { BackgroundColor = Color.Green };
}
login = !login;
}
I print the popAction and PushAction in your code, you will find that the popAction is executed before PushAction.
Solution:
You should perform popAction after pushModalAction is completed.
I moved the Navigation.PopModalAsync(); from the btn.clicked to HandleLogOut and then it works well.
btn.Clicked += async (sender, e) =>
{
MessagingCenter.Send<object>(this, "LoginLogout");
};
In handle logout:
async Task HandleLogOut()
{
if (login)
{
Console.WriteLine("PushModalAction");
await MainPage.Navigation.PushModalAsync(new Main1 { BackgroundColor = Color.Orange });
Console.WriteLine("popAction");
MainPage.Navigation.PopModalAsync();
}
else
{
MainPage = new Main1 { BackgroundColor = Color.Green };
}
login = !login;
}