NullPointerException while using dagger-2 to inject preferences in fragment

Question

I am getting error in injecting preferences:

Can't figure out the problem.

Here are some of the classes i am using :

The AppModule class

 @Module
    public class AppModule {
        private final MyApplication app;

        public AppModule(MyApplication app) {
            this.app = app;
        }

        @Provides
        @Singleton
        public Context provideContext() {
            return app;
        }

        @Provides
        @Singleton
        SharedPreferences providesSharedPreference() {
            return PreferenceManager.getDefaultSharedPreferences(app);
        }
    }

// The AppComponent interface

    @Singleton
    @Component(
            modules = {
                    AppModule.class,
            }
    )

    public interface AppComponent {

        void inject(DisplayFragment fragment);

    }

THE APPLICATION class

public class MyApplication extends Application {

    private static MyApplication instance = new MyApplication();
    private static AppComponent appComponent;

    public static MyApplication getInstance() {
        return instance;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        getAppComponent();
    }

    public AppComponent getAppComponent() {
        if (appComponent == null) {
            appComponent = DaggerAppComponent.builder()
                    .appModule(new AppModule(this))
                    .build();
        }
        return appComponent;
    }
}

Finally in a fragment i am doing :

public class DisplayFragment extends Fragment implements View.OnClickListener {
...
    @Inject
    SharedPreferences prefs;

    @Inject
    public DisplayFragment() {
        MyApplication.getInstance().getAppComponent().inject(this);
    }
..
}

I am getting this error and application is crashing.

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                       at android.content.ContextWrapper.getPackageName(ContextWrapper.java:133)
                                                       at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:390)
                                                       at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:385)
                                                       at dagger.module.AppModule.providesSharedPreference(AppModule.java:34)
                                                       at dagger.module.AppModule_ProvidesSharedPreferenceFactory.get(AppModule_ProvidesSharedPreferenceFactory.java:23)
                                                       at dagger.module.AppModule_ProvidesSharedPreferenceFactory.get(AppModule_ProvidesSharedPreferenceFactory.java:8)
                                                       at dagger.internal.ScopedProvider.get(ScopedProvider.java:47)
                                                       at ui.DisplayFragment_MembersInjector.injectMembers(DisplayFragment_MembersInjector.java:29)
                                                       at ui.DisplayFragment_MembersInjector.injectMembers(DisplayFragment_MembersInjector.java:8)
                                                       at dagger.component.DaggerAppComponent.inject(DaggerAppComponent.java:45)
                                                       at ui.DisplayFragment.<init>(DisplayFragment.java:37)
                                                       at ui.DisplayFragment.newInstance(DisplayFragment.java:41)
                                                       at ui.MainActivity$MyPagerAdapter.getItem(MainActivity.java:86)
                                                       at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:101)
                                                       at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:1034)
                                                       at android.support.v4.view.ViewPager.populate(ViewPager.java:1182)
                                                       at android.support.v4.view.ViewPager.populate(ViewPager.java:1116)
                                                       at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1642)
                                                       at android.view.View.measure(View.java:19324)
                                                       at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:825)
                                                       at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:511)
                                                       at android.view.View.measure(View.java:19324)
                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6113)
                                                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:223)
                                                       at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
                                                       at android.view.View.measure(View.java:19324)
                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6113)
                                                       at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:393)
                                                       at android.view.View.measure(View.java:19324)
                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6113)
                                                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:223)
                                                       at android.view.View.measure(View.java:19324)
                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6113)
                                                       at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1723)
                                                       at android.widget.LinearLayout.measureVertical(LinearLayout.java:788)
                                                       at android.widget.LinearLayout.onMeasure(LinearLayout.java:648)
                                                       at android.view.View.measure(View.java:19324)
                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6113)
                                                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:223)
                                                       at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2694)
                                                       at android.view.View.measure(View.java:19324)
                                                       at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2545)
                                                       at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1454)
                                                       at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1709)
                                                       at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1335)
                                                       at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6816)
                                                       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:894)
                                                       at android.view.Choreographer.doCallbacks(Choreographer.java:696)
                                                       at android.view.Choreographer.doFrame(Choreographer.java:631)
                                                       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:880)
                                                       at android.os.Handler.handleCallback(Handler.java:815)
                                                       at android.os.Handler.dispatchMessage(Handler.java:104)
                                                       at android.os.Looper.loop(Looper.java:207)
                                                       at android.app.ActivityThread.main(ActivityThread.java:5896)
                                                    at ja

Someone please help..

Can you provide a solution here.. I know what an NPE is.. Having a frustating problem here.. — Manvendra Sah, Jan 13 '17 at 12:04

score 2 · Answer 1 · edited Mar 02 '17 at 09:24

2

You probably need to change providesSharedPreference() to :

@Provides
@Singleton
SharedPreferences providesSharedPreference(Context context) {
    return PreferenceManager.getDefaultSharedPreferences(context);
}

and do the injection in onCreateView() method, because current setup does not garantee that the Context has been intialized when the fragment constructor is called.

edited Mar 02 '17 at 09:24

nilsi

10,351
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answered Jan 13 '17 at 08:38

Nikola Despotoski

49,966
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148

Tried your solution but iT didn't help.. – Manvendra Sah Jan 13 '17 at 11:20
1

You didnt try you just copy and pasted. :) – Nikola Despotoski Jan 13 '17 at 12:02

laenger · Answer 2 · 2017-01-13T08:58:12.687

1

I am not sure how your application singleton is supposed to work (MyApplication instance = new MyApplication()) since Android creates the Application for you. This is also the reason for your crash: you pass that selfmade, uninitialized instance to the PreferenceManager.

In your Fragment, try injecting in onCreateView(), e.g., like this:

public class DisplayFragment extends Fragment {
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        ((MyApplication) getActivity().getApplication()).getAppComponent().inject(this);
        return ...; // your fragment view
    }
}

edited Jan 13 '17 at 08:58

answered Jan 13 '17 at 08:52

laenger

991
1
10
20

I did as u suggested. I removed tge application instatntiation and moved the injection to onCreateView (). But now i am getting java.lang.ClassCastException: android.app.Application cannot be cast to app.MyApplication – Manvendra Sah Jan 13 '17 at 11:27
1

It seems like you simply did not define your custom Application class in the manifest. Add `android:name=".MyApplication"` to your tag. – laenger Jan 13 '17 at 11:54
Thanks a lot.. u made my day.. :-) – Manvendra Sah Jan 13 '17 at 12:06

NullPointerException while using dagger-2 to inject preferences in fragment

2 Answers2