VS2019 更新给出 FragmentManager 错误

Question

I recently upgraded my installation of VisualStudio 2019 from 16.4.19 to 16.9.3 After cleaning up a few errors, it builds just fine. When I try to deploy and run it on a 7.0 tablet, I get the message:

Java.Lang.IllegalStateException Message=FragmentManager has not been attached to a host.

Here is the code that generates the problem:

void Navigate(Android.Support.V4.App.Fragment fragment)
{
    var transaction = base.SupportFragmentManager.BeginTransaction();
    transaction.Replace(Resource.Id.contentFrame, fragment);
    transaction.Commit();
}

And this code calls it:

void OnMenuItemSelected(object sender, Android.Support.Design.Widget.NavigationView.NavigationItemSelectedEventArgs e)
{
    Vars.OnMain = false;    //turn off screen updates until mainscreen is open
    switch (e.MenuItem.ItemId)
    {
        case Resource.Id.aboutMenuItem: Navigate(new AboutFragment()); break;
        case Resource.Id.catalogMenuItem: Navigate(new CatalogFragment()); break;
        //case Resource.Id.itemMenuItem: Navigate(new ItemFragment()); break;
        case Resource.Id.helpMenuItem: Navigate(new HelpFragment()); break;
        case Resource.Id.settingsMenuItem: Navigate(new SettingsFragment()); break;
        case Resource.Id.coordinateMenuItem: Navigate(new CoordinateFragment()); break;
        case Resource.Id.mainMenuItem: Navigate(new MainScreenFragment()); break;
        default: return;
    }

    e.MenuItem.SetChecked(true);

    //var drawerLayout = FindViewById<Android.Support.V4.Widget.DrawerLayout>(Resource.Id.drawerLayout);
    drawerLayout.CloseDrawer(Android.Support.V4.View.GravityCompat.End);
}

The App has been running for years and is too large to post here.

Has something changed in the VS2019 environment during the last year that would cause this problem?

Thanks for your help, Dan

Answer 1

From the following code you posted,we found that you're getting the fragment manager from the base variable. Where does base itself get the FragmentManager ? When you Navigate , the activity maybe been destroyed and recreated. Therefore, you might need to get a new FragmentManager.

void Navigate(Android.Support.V4.App.Fragment fragment)
{
    var transaction = base.SupportFragmentManager.BeginTransaction();
    transaction.Replace(Resource.Id.contentFrame, fragment);
    transaction.Commit();
}

So, you can try to use the following code:

FragmentTransaction transaction = FragmentManager.BeginTransaction ();
transaction.Replace(Resource.Id.contentFrame, fragment);
transaction.Commit();