dagger-2を使用してフラグメント内にプリファレンスを挿入中にNullPointerExceptionが発生する

Question

プリファレンスにエラーが表示される：

問題を特定できません。

AppModuleクラス

@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); 

    } 

Applicationクラス私がやっているフラグメントで最後に

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; 
    } 
} 

：

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

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

ここ

は、私が使用していたクラスの一部です

このエラーが発生し、アプリケーションがクラッシュしています。現在の設定がContextがあったことをgaranteeていないため、

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

とonCreateView()方法で注入を実行します。誰か助けてください

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 

..

Answer 1

はおそらくにprovidesSharedPreference()を変更する必要がありますフラグメントコンストラクタが呼び出されると初期化されます。

Answer 2

Androidがアプリケーションを作成するため、アプリケーションのシングルトンがどのように動作すると思われますか（MyApplication instance = new MyApplication()）。これもあなたのクラッシュの原因です。初期設定されていない自作のインスタンスをPreferenceManagerに渡します。ここfrustating問題を持つ

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 
    } 
}