Mvvmcross: framelayout doesn't show fragment after activity

Question

So I have a problem with a fragment not showing inside a MvxCachingFragmentCompatActivity.

The pattern I use to get to the problem is as follows:

1. Register a activity.
2. Navigate to another activity that extends MvxCachingFragmentCompatActivity
3. Load the fragment using await _navigationService.Navigate<[TheFragmentViewModel]>();
4. Fragment loading is called but it doesn't show anything.

Fragment declaration:

[MvxFragment(typeof(MainViewModel), Resource.Id.content_frame, true)]
[Register(nameof(FirstFragment))]
public class FirstFragment : MvxFragment<FirstViewModel>
{
    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        base.OnCreateView(inflater, container, savedInstanceState);
        var view = this.BindingInflate(Resource.Layout.FirstView, container, false);
        return view;
    }
}

Main activity: (nothing special I think)

[Activity(Label = "Fragment View")]
public class MainActivity : MvxCachingFragmentCompatActivity<MainViewModel>
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        SetContentView(Resource.Layout.MainView);
    }
}

Main viewmodel

public class MainViewModel : MvxViewModel
{
    private readonly IMvxNavigationService _navigationService;

    public MainViewModel(IMvxNavigationService navigationService)
    {
        _navigationService = navigationService;
        Init();
    }

    public async void Init()
    {
        await _navigationService.Navigate<FirstViewModel>();
    }
}

Main activity layout: (very simple layout)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:local="http://schemas.android.com/apk/res-auto"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
  <FrameLayout
    android:id="@+id/content_frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />
</LinearLayout> 

I also added a sample on github: Github link.

I also added a bug report on the Mvvmcross github, but I am not sure if it is a bug on my part or theirs?

Answer 1

You should never use async void or start an async task from a non async command. These are the first problems. Also your Initialize is not called because you are not using RegisterNavigationServiceAppStart<>(). Another thing is that you are supposed to navigate directly to a fragment and not first to the activity, because MvvmCross will handle that.

Another hint will be to use Dependency injection to resolve IMvxNavigationService.