Using Android Architecture Components in Organizer App

Using Android Architecture Components in Organizer App

In the Open Event Organizer Android App there is an issue with the Memory leaks, Data persistence on configuration changes and difficulty in managing the Activity lifecycle. So as to deal with these issues we have implemented Android Architecture Components.

The first step towards moving on with AAC’s was the conversion of a presenter class to a ViewModel class and then implementing LiveData in the refactored class.

LiveData

It is an Observable data holder. It notifies the observers whenever there is change in the data so that the UI can be updated.

Livedata is also bound to the lifecycle which means that it will be observing changes only when the activity is in started or resumed state and hence there is no chance of memory leaks or null pointer exceptions.

ViewModel

The ViewModel class is designed to hold and manage UI-related data in a life-cycle conscious way. This allows data to survive configuration changes such as screen rotations.

In the following I’ll be explaining how the LoginViewModel class was made in the Orga App.

Steps

  • Creating one’s own custom ViewModelFactory. This is done so as to follow the Single Responsibility Principle. This custom class extends the ViewModelProvider.Factory and handles the creation of View Models. Adding this class also ensures that a Constructor can also get injected in the View Model class.
@Singleton
public class OrgaViewModelFactory implements ViewModelProvider.Factory {

  private final Map<Class<? extends ViewModel>, Provider<ViewModel>> creators;

  @Inject
  public OrgaViewModelFactory(Map<Class<? extends ViewModel>, Provider<ViewModel>> creators) {
      this.creators = creators;
  }

  @NonNull
  @Override
  @SuppressWarnings({“unchecked”, “PMD.AvoidThrowingRawExceptionTypes”, “PMD.AvoidCatchingGenericException”})
  public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
      Provider<? extends ViewModel> creator = creators.get(modelClass);
      if (creator == null) {
          for (Map.Entry<Class<? extends ViewModel>, Provider<ViewModel>> entry : creators.entrySet()) {
              if (modelClass.isAssignableFrom(entry.getKey())) {
                  creator = entry.getValue();
                  break;
              }
          }
      }
      if (creator == null) {
          throw new IllegalArgumentException(“unknown model class “ + modelClass);
      }
      try {
          return (T) creator.get();
      } catch (Exception e) {
          throw new RuntimeException(e);
      }
  }
}
  • Injecting this custom ViewModelFactory into the ViewModelModule. Adding the method bindLoginViewModel with the LoginViewModel as its parameter. Always add any new ViewModel class into the ViewModelModule otherwise it might show DaggerAppComponent errors.
@Module
public abstract class ViewModelModule {

  @Binds
  @IntoMap
  @ViewModelKey(LoginViewModel.class)
  public abstract ViewModel bindLoginViewModel(LoginViewModel loginViewModel);

  @Binds
  public abstract ViewModelProvider.Factory bindViewModelFactory(OrgaViewModelFactory factory);

}
  1. Refactoring the LoginPresenter to LoginViewModel class and extending it to ViewModel.
  2. In the fragment class injecting the ViewModelProviderFactory.
@Inject
ViewModelProvider.Factory viewModelFactory;
  • Pass this parameter in the ViewModelProviders.of( ) method as follows:
loginFragmentViewModel = ViewModelProviders.of(this, viewModelFactory).get(LoginViewModel.class);
  • Now the only task in hand is the use of LiveData in the ViewModels and observing the LiveData from the Fragments. In the following LiveData has been applied to observe the state of Progress Bar. When the login button is pressed, the value of MutableLiveData<Boolean> progress is set to true.
public void login() {
  compositeDisposable.add(loginModel.login(login)
      .doOnSubscribe(disposable -> progress.setValue(true))
      .doFinally(() -> progress.setValue(false))
      .subscribe(() -> isLoggedIn.setValue(true),
          throwable -> error.setValue(ErrorUtils.getMessage(throwable))));
}

 

  • This change in state is observed by the following code in the fragment class:
loginFragmentViewModel.getProgress().observe(this, this::showProgress);

On observing this, the showProgress is called which handles the visibility if the progress bar. Currently as the progress value was set to True, the progress bar is visible till the processing goes on.

  • Once the login takes place the progress of the LoginViewModel is set to false and the progress bar gets hidden, again which gets observed in the fragment class.

References:

https://android.jlelse.eu/android-architecture-components-livedata-1ce4ab3c0466

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