Android Studio - 从片段类打开导航抽屉

Question

我正在尝试通过单击按钮打开并使用单独的片段填充导航抽屉。抽屉本身只是在activity_main.xml 中声明的空RelativeLayouts。

activity_main.xml：

<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">

<!--Main View-->
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="xxx.MainActivity">
</RelativeLayout>

<!--Left drawer-->
<RelativeLayout android:id="@+id/drawer_left"
    android:layout_width="290dp"
    android:layout_height="match_parent"
    android:layout_gravity="start">
</RelativeLayout>

<!--Right drawer-->
<RelativeLayout android:id="@+id/drawer_right"
    android:layout_width="290dp"
    android:layout_height="match_parent"
    android:layout_gravity="end">
</RelativeLayout>

main_view 在 MainActivity 中填充了一个片段，所以它看起来像这样：

MainActivity 类：

public class MainActivity extends AppCompatActivity {

android.app.FragmentManager fragmentManager;
android.app.FragmentTransaction fragmentTransaction;


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

    fragmentManager = getFragmentManager();

    //Set fragment
    Frag1 frag1 = new Frag1();
    fragmentTransaction = getFragmentManager().beginTransaction();
    fragmentTransaction.add(R.id.fragment_container,frag1).commit();
}

Frag1 类：

public class Frag1 extends Fragment {
ImageButton imageButtonOpenDrawer;

DrawerLayout mDrawerLayout;
RelativeLayout mDrawer_left;

android.app.FragmentManager fragmentManager;
android.app.FragmentTransaction fragmentTransaction;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    return inflater.inflate(R.layout.frag1, container, false);
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    View v = getView();
    imageButtonOpenDrawer = (ImageButton) v.findViewById(R.id.imageButtonOpenDrawer);

    fragmentManager = getFragmentManager();

    mDrawerLayout = (DrawerLayout) v.findViewById(R.id.drawer_layout);
    mDrawer_left = (RelativeLayout) v.findViewById(R.id.drawer_left);

    imageButtonOpenDrawer.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            DrawerFragment drawerFragment = new DrawerFragment();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.add(R.id.fragment_container,drawerFragment).commit();
        }
    });
}

在 MainActivity 类中执行相同的原理。但是当我尝试从 Fragments 类打开抽屉时，会抛出这个空指针错误：

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“void android.support.v4.widget.DrawerLayout.openDrawer(android.view.View)”

Answer 1

尝试检查getView()的返回。

我认为frag1 的根视图在R.layout.frag1 中，它没有drawer_layout 和drawer_left。