Replace fragments in viewpager Mvvmcross - xamarin.android

Question

tldr: How can I replace fragments in viewpager using MvvmCross?
I have tried to replace a fragment in a viewpager using the approach described at How to replace fragments within a Viewpager. The idea is that within the view pager a "RootFragment" is shown. However, it is replaced by a first fragment. If needed, it can also be replaced by a second fragment, third fragment and so on. As more fragments are added, they are added to the backstack as well.
So this would be a snippet of the code for the "RootFragment"
public class RootView : MvxFragment
{
public override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
}
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
var view = inflater.Inflate(Resource.Layout.root_fragment, container, false);
var transaction = FragmentManager.BeginTransaction();
var fragment = FirstView.NewInstance();
transaction.Replace(Resource.Id.root_frame, fragment);
transaction.Commit();
return view;
}
}
Then, a snippet for the "First fragment" would be
[MvxFragmentPresentation(typeof(MainViewModel),
Resource.Id.root_frame, true)]
public class ScoringView : MvxFragment<FirstViewModel>
{
public override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
// Create your fragment here
}
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
base.OnCreateView(inflater, container, savedInstanceState);
return this.BindingInflate(Resource.Layout.first_fragment, null);
}
}
The layout for "RootFragment" is:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:background="#000"
android:layout_height="match_parent"
android:id="#+id/root_frame" />
The code for "FirstViewModel" would be:
public class FirstViewModel: MvxViewModel
{
private IMvxAsyncCommand _openPreguntasCommand;
private IMvxNavigationService _navigationService;
public IMvxAsyncCommand OpenSecondCommand { get => _openSecondCommand?? (new MvxAsyncCommand(async () =>
{
await _navigationService
.Navigate<SecondViewModel>();
})); }
public FirstViewModel(IMvxNavigationService navigationService)
{
_navigationService = navigationService;
}
}
I have tried to accomplish this task using a PresentationHint. I modified the code used in How to clear entire Backstack using viewmodel(navigation service) to suit my needs to no avail. So perhaps a custom presenter could be an option. I could override one "OnBeforeFragmentChanging" or some other related method. What I ended up doing was that used the MvxFragmentPresentation attribute and I set the fragmentContentId to the Id of the placeholder in the "RootFragment" layout. However, it seems to me that there has to be a better way.
[MvxFragmentPresentation(typeof(MainViewModel), Resource.Id.root_frame, true)]

Answer 1

Did you try the Playground example that comes with the MvvmCross source code? There is a good implementation of fragments