Marian Pa┼║dzioch Marian Pa┼║dzioch - 3 years ago 134
Android Question

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

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) or network:

Shared Prefs|
|<->Repository<->Model<->Presenter<->View
Network|


But to put my hands on Shared Preferences I have to put somewhere line like

presenter = new Presenter(getApplicationContext());


I use
onRetainCustomNonConfigurationInstance
/
getLastCustomNonConfigurationInstance
pair to keep Presenter "retained".

public class MyActivity extends AppCompatActivity implements MvpView {

@Override
protected void onCreate(Bundle savedInstanceState) {
//...
presenter = (MvpPresenter) getLastCustomNonConfigurationInstance();

if(null == presenter){
presenter = new Presenter(getApplicationContext());
}

presenter.attachView(this);
}

@Override
public Object onRetainCustomNonConfigurationInstance() {
return presenter;
}

//...
}


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

Answer Source

Your Presenter should not be Context dependent in the first place. If your presenter needs SharedPreferences you should pass them in in the constructor.
If your presenter needs a Repository, again, put that in the constructor. I highly suggest watching Google clean code talks since they do a really good job on explaining why you should use a proper API.

This is proper dependency management, which will help you write clean, maintainable, and testable code. And whether you use dagger, some other DI tool, or supply the objects yourself is irrelevant.

public class MyActivity extends AppCompatActivity implements MvpView {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        SharedPreferences preferences = // get your preferences
        ApiClient apiClient = // get your network handling object
        Repository repository = new Repository(apiClient, preferences);
        presenter = new Presenter(repository);
    }
}

This object creation can be simplified by using a factory pattern, or some DI framework like dagger, but as you can see above neither Repository nor your presenter depends on a Context. If you want to supply your actual SharedPreferences only their creation of them will depend on the context.

Your repository depends on some api client and SharedPreferences, your presenter depends on the Repository. Both classes can easily be tested by just supplying mocked objects to them.

Without any static code. Without any side effects.

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