How to use Shared Preferences in MVP without Dagger and not causing Presenter to be Context dependent?

Question

I\'m trying to implement MVP without Dagger (for learning purposes). But I got to the problem - I use Repository patter to get raw data either from cache (Shared Preferences

Answer 1

Another approach can also be found in the Android Architecture libraries:

As the Shared Preferences depends on a context, it solely should know about it. To have things in one place, I choose a Singleton to manage this. It consists of two classes: the Manager (i.e. the SharePreferenceManager or ServiceManager or whatever), and an initializer which injects the Context.

class ServiceManager {

  private static final ServiceManager instance = new ServiceManager();

  // Avoid mem leak when referencing context within singletons
  private WeakReference context

  private ServiceManager() {}

  public static ServiceManager getInstance() { return instance; }

  static void attach(Context context) { instance.context = new WeakReference(context); }

  ... your code...

}

The initializer is basically an empty Provider (https://developer.android.com/guide/topics/providers/content-providers.html), which is registered in the AndroidManifest.xml and loaded when the app starts:

public class ServiceManagerInitializer extends ContentProvider {

    @Override
    public boolean onCreate() {
        ServiceManager.init(getContext());

        return false;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        return null;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        return null;
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }
}

All function are default implementations except the onCreate, which injects the required context into our manager.

Last step to get this working is to register the provider in the manifest:

This way, your service manager is decoupled from any external context initialization. It now can be completely replaced with another implementation which is context-independent.