android how to save state properly?

Question

Java

I dealt with a test project from the course on Android development from e-legion, the lesson itself - https://www.youtube.com/watch?v=cH9UxmZwGO4 , the project from the speaker (Dmitry Kalita) - https://github.com/ rusmonster/signin.
The structure looks like this:
MainActivity.java:

public class SignInActivity extends Activity implements SignInModel.Observer {
  private SignInModel mSignInModel;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    mSubmit.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(final View v) {
        mSignInModel.signIn(userName, password);
      }
    });
    //Восстановление SignInModel
    mSignInModel.registerObserver(this);
  }

  @Override
  protected void onDestroy() {
    mSignInModel.unregisterObserver(this);
    if (isFinishing()) {
      mSignInModel.stopSignIn();
    }
  }

  @Override
  public void onSignInStarted(final SignInModel signInModel) {
  }

  @Override
  public void onSignInSucceeded(final SignInModel signInModel) {
  }

  @Override
  public void onSignInFailed(final SignInModel signInModel) {
  }
}

SignInModel.java

public class SignInModel {
  private final SignInObservable mObservable = new SignInObservable();

  public void signIn(final String userName, final String password) {
    if (mIsWorking) {
      return;
    }
    mObservable.notifyStarted();
  }

  public void registerObserver(final Observer observer) {
    mObservable.registerObserver(observer);
    if (mIsWorking) {
      observer.onSignInStarted(this);
    }
  }

  public void unregisterObserver(final Observer observer) {
    mObservable.unregisterObserver(observer);
  }

  private class SignInObservable extends Observable<Observer> {
    public void notifyStarted() {
      for (final Observer observer : mObservers) {
        observer.onSignInStarted(SignInModel.this);
      }
    }

    public void notifySucceeded() {
      for (final Observer observer : mObservers) {
        observer.onSignInSucceeded(SignInModel.this);
      }
    }

    public void notifyFailed() {
      for (final Observer observer : mObservers) {
        observer.onSignInFailed(SignInModel.this);
      }
    }
  }
}

It may be that such an architecture is far from the best, but it is easy to understand; I have little experience, I decided to use it (now I'm looking towards pattern A).
But the question arose - what to do if there are several such tasks: for example, downloading info and uploading photos within one Activity.
You can implement several models for one Activity, but this will be redundant code (because they are essentially very similar), you can also implement everything within the same model, but then you need additional code to determine which process is currently running (so that in onCreate call the corresponding method, for example, when re-creating - either onLoadPhotoStarted , or onLoadInfoStarted , etc.), please tell me how to do all this correctly.

Answer 1

It is not necessary to store data of different entities in one model, and there is nothing wrong with using several models in one activity. In the end, you can have a complex ui where each view is represented by a specific data model. But it’s not worth duplicating the code either, try to analyze what the models have in common, and somehow group them through inheritance or composition.