How to set up dependency injection using Dagger for things other than Activities and Fragments?

Question

I started setting up dependency injection using Dagger as follows. Please feel encouraged to correct my implementation since I might have mistakes in there! The implementation follows the android-simple example provided by the project. In the following you can see how I successfully added dependency injection for Activities and Fragments. I try to keep it easy for now so I decided to inject Timber as a logger substitution for Android's log util.

import android.app.Application;
import java.util.Arrays;
import java.util.List;
import dagger.ObjectGraph;
import com.example.debugging.LoggingModule;

public class ExampleApplication extends Application {

    private ObjectGraph mObjectGraph;

    protected List<Object> getModules() {
        return Arrays.asList(
                new AndroidModule(this),
                new ExampleModule(),
                new LoggingModule()
        );
    }

    private void createObjectGraphIfNeeded() {
        if (mObjectGraph == null) {
            Object[] modules = getModules().toArray();
            mObjectGraph = ObjectGraph.create(modules);
        }
    }

    public void inject(Object object) {
        createObjectGraphIfNeeded();
        mObjectGraph.inject(object);
    }
}

By now the AndroidModule is not used anywhere it but might be helpful when a Context and LayoutInflater is needed e.g. in CursorAdapters.

import android.content.Context;
import android.view.LayoutInflater;
import javax.inject.Singleton;
import dagger.Module;
import dagger.Provides;

/**
 * A module for Android-specific dependencies which require a {@link Context} 
 * or {@link android.app.Application} to create.
 */
@Module(library = true)
public class AndroidModule {
    private final ExampleApplication mApplication;

    public AndroidModule(ExampleApplication application) {
        mApplication = application;
    }

    /**
     * Allow the application context to be injected but require that it be 
     * annotated with {@link ForApplication @Annotation} to explicitly 
     * differentiate it from an activity context.
     */
    @Provides @Singleton @ForApplication Context provideApplicationContext() {
        return mApplication;
    }

    @Provides @Singleton LayoutInflater provideLayoutInflater() {
        return (LayoutInflater) mApplication
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }
}

I am not sure what application-specific providers would go here. I stay with logging for now.

import dagger.Module;

@Module(
        complete = false
)
public class ExampleModule {
    public ExampleModule() {
         // TODO put your application-specific providers here!
    }
}

I prepared LoggingModule which provides access to Timber.

package com.example.debugging;

import javax.inject.Singleton;

import dagger.Module;
import dagger.Provides;
import com.example.BuildConfig;
import com.example.activities.BaseFragmentActivity;
import com.example.activities.DetailsActivity;
import com.example.fragments.BaseListFragment;
import com.example.fragments.ProfilesListFragment;
import timber.log.Timber;

@Module(injects = {
        // Activities
        BaseFragmentActivity.class,
        DetailsActivity.class,
        // Fragments
        BaseListFragment.class,
        ProfilesListFragment.class
})
public class LoggingModule {

    @Provides @Singleton Timber provideTimber() {
        return BuildConfig.DEBUG ? Timber.DEBUG : Timber.PROD;
    }
}

The base class for Activities injects itself into the object graph ...

package com.example.activities;

import android.os.Bundle;    
import com.actionbarsherlock.app.SherlockFragmentActivity;    
import javax.inject.Inject;
import com.example.ExampleApplication;
import timber.log.Timber;

public abstract class BaseFragmentActivity extends SherlockFragmentActivity {

    @Inject Timber mTimber;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // ...
        super.onCreate(savedInstanceState);
        ((ExampleApplication) getApplication()).inject(this);
    }
}

... and any sub class benefits from Timber being already present.

package com.example.activities;

import android.os.Bundle;
import com.example.R;

public class DetailsActivity extends BaseFragmentActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_details);
        mTimber.i("onCreate");
        // ...
    }
}

Same for Fragments: the base class does the dirty job ...

package com.example.fragments;

import android.os.Bundle;
import com.actionbarsherlock.app.SherlockListFragment;
import javax.inject.Inject;
import com.example.ExampleApplication;
import timber.log.Timber;

public abstract class BaseListFragment extends SherlockListFragment {

    @Inject Timber mTimber;

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        ((ExampleApplication) getActivity().getApplication()).inject(this);
    }

}

... and the sub class benefits from its super class.

package com.example.fragments;

import android.os.Bundle;

public class ProfilesListFragment extends BaseListFragment {

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        // TODO This might be a good example to inject resources
        // in the base class. But how?
        setEmptyText(getResources()
           .getString(R.string.profiles_list_no_content));
        mTimber.i("onActivityCreated");
        // ...
    }

}

So far so good. But how can inject Timber into BaseCursorAdapter, BaseContentProvider, BaseSQLiteOpenHelper, BaseService, BaseAsyncTask and static helper methods?

The deprecated android example by Christopher Perry points out how to inject an Adapter into a ListFragment but not how to inject Context, Resources, LayoutInflater, Cursor into the (Cursor)Adapter or just Timber.

---

References:

• Dagger
• android-simple example
• Jesse Wilson - Dagger: A Fast Dependency Injector for Android and Java
• Eric Burke - Android App Anatomy

Answer 1

Check out Andy Dennie's examples for injecting in different scenarios:

https://github.com/adennie/fb-android-dagger

Some points where I inject:

• Activity, Service, and Fragment subclasses: in onCreate
• BroadcastReceiver subclasses (includes, e.g. AppWidgetProvider): in onReceive