Android MVVM: How to handle network request failiures?

Question

I am new to Android Arch components. I am trying to make a basic todo app using Android View Model and Live Data. What is the best way to make network calls when following MVVM pattern? I need to show a progress bar when a network request starts and dismiss it when the call is complete and in case of errors I need to display a snackbar with the relevant error message. Is it possible to do this without using an AsyncTask?

Remote Repository Class:

public class RemoteRepository {
private APIService apiService;

public RemoteRepository (APIService apiService) {
    this.apiService= apiService;
}

public LiveData<List<Project>> getList(String userId) {
    final MutableLiveData<List<Project>> data = new MutableLiveData<>();

    apiService.getList(userId).enqueue(new Callback<List<Project>>() {
        @Override
        public void onResponse(Call<List<Project>> call, Response<List<Project>> response) {
            data.setValue(response.body());
        }

        @Override
        public void onFailure(Call<List<Project>> call, Throwable t) {
            // What to do to show snackbar in activity
        }
    });
    return data;
}

Do we need to use an async task and manage the UI in its preExecute and postExecute callbacks? Or is it possible to do it with Observable Livedata objects?

Answer 1

You can do it this way.

Create a class that has a Throwable and desire success result object. create a constructor or getter setter method to set values. ProjectRepoClass is an example of it.

Project Repo Class::

public class ProjectRepoModel {

private List<Project> mList;
private Throwable mThrowable;

public ProjectRepoModel (List<Project> mList) {
    mList= mList;
}

public ProjectRepoModel (Throwable throwable) {
    mThrowable = throwable;
}

public List<Project> getList() {
    return mList;
}

public Throwable getThrowable() {
    return mThrowable;
}

}

Set value according to API result. it can be an error or success response and return it.

Return data:

public LiveData<List<Project>> getList(String userId) {
final MutableLiveData<ProjectRepoModel > data = new MutableLiveData<>();

apiService.getList(userId).enqueue(new Callback<List<Project>>() {
    @Override 
    public void onResponse(Call<List<Project>> call, Response<List<Project>> response) { 
        data .setValue( new ProjectRepoModel (response.body()));
    } 

    @Override 
    public void onFailure(Call<List<Project>> call, Throwable t) { 
        data .setValue( new ProjectRepoModel (t));
    } 
}); 
return data;
} 

Create Observable for live data in the UI part and make a check for error and display results according to it.

Observe result In UI Like this:

if (mModel.getThrowable() != null)
  {
        // Show error
  } else {

       // display success result

  }

This how you can achieve the error handle from the repository in MVVM.