Question

getApp()方法正在返回null。知道为什么吗？

public class App extends Application {

    private static App app;

    private BoxStore boxStore;

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

        app = this;

        boxStore = MyObjectBox.builder().androidContext(App.this).build();
        if(BuildConfig.DEBUG)
        {
            new AndroidObjectBrowser(boxStore).start(this);
        }

    }

    public static App getApp() {
        return app;
    }

    public BoxStore getBoxStore() {
        return boxStore;
    }

}

从以下活动中调用getApp()方法：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    BoxStore boxStore = App.getApp().getBoxStore();
    Box<ListEntryObject> listEntryObjectBox = boxStore.boxFor(ListEntryObject.class);

    sharedPreferences = getSharedPreferences("TYPE_OF_ACTION", Context.MODE_PRIVATE);
    editor = sharedPreferences.edit();
    editor.putInt("sourceToDest", 0);
    editor.apply();

    sharedPreferences = getSharedPreferences("POSITION" , Context.MODE_PRIVATE);
    editor = sharedPreferences.edit();
    editor.putInt("position", 0);
    editor.apply();

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            sharedPreferences = getSharedPreferences("TYPE_OF_ACTION", Context.MODE_PRIVATE);
            editor = sharedPreferences.edit();

            editor.putInt("sourceToDest", 0);
            editor.apply();

            fragmentManager = getSupportFragmentManager();
            entryDialogFragment = new EntryDialogFragment();

            entryDialogFragment.show(fragmentManager, "Sample Fragment");

        }
    });

    entryObjectList = new ArrayList<>();

}

Answer 1

请务必将此类（App）链接到Manifest.xml中的应用程序标记，如下面的代码所示

<application
    android:name="package.MyClass"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme">
    ...
 </application>

获取App对象返回null

1 个答案: