java - 使用抽屉导航时尝试从空对象引用的字段 'int android.support.v4.app.Fragment.mContainerId' 读取

Question

下面是我在使用抽屉导航进行导航时在 Android Studio 中遇到的错误的 StackTrace。这是一个新错误，因为我以前没有发生过。所以我不确定如果我改变了什么。

08-11 23:16:37.823 15951-15951/com.example.aids.a09application
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aids.a09application, PID: 15951
java.lang.NullPointerException: Attempt to read from field 'int android.support.v4.app.Fragment.mContainerId' on a null object reference
at android.support.v4.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1017)
at android.support.v4.app.FragmentTransition.calculateFragments(FragmentTransition.java:976)
at android.support.v4.app.FragmentTransition.startTransitions(FragmentTransition.java:95)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2146)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2103)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2013)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:710)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6692)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)

下面是 Java 类，其中我有我的抽屉导航的 fragment 事务。

public class MainActivity extends AppCompatActivity {
    DrawerLayout drawerLayout;
    Toolbar toolbar;
    ActionBarDrawerToggle actionBarDrawerToggle;
    FragmentTransaction fragmentTransaction;
    NavigationView navigationView;
    Intent intent;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

        actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.drawer_open, R.string.drawer_close);

        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.add(R.id.main_container, new HomeFragment());
        fragmentTransaction.commit();
        getSupportActionBar().setTitle("Drift Fan");
        navigationView = (NavigationView) findViewById(R.id.navigation_view);
        navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.Home:
                        fragmentTransaction = getSupportFragmentManager().beginTransaction();
                        fragmentTransaction.replace(R.id.main_container, new HomeFragment());
                        fragmentTransaction.commit();
                        getSupportActionBar().setTitle("Home Fragment");
                        item.setCheckable(true);
                        drawerLayout.closeDrawers();
                        break;
                    case R.id.my_account:
                        fragmentTransaction = getSupportFragmentManager().beginTransaction();
                        fragmentTransaction.replace(R.id.main_container, new myAccountFragment());
                        fragmentTransaction.commit();
                        getSupportActionBar().setTitle("My Account");
                        item.setCheckable(true);
                        drawerLayout.closeDrawers();
                        break;
                    case R.id.nav_about:
                        fragmentTransaction = getSupportFragmentManager().beginTransaction();
                        fragmentTransaction.replace(R.id.main_container, new AboutDriftingFragment());
                        fragmentTransaction.commit();
                        getSupportActionBar().setTitle("About Drifting");
                        item.setCheckable(true);
                        drawerLayout.closeDrawers();
                        break;
                    case R.id.nav_shop:
                        fragmentTransaction = getSupportFragmentManager().beginTransaction();
                        fragmentTransaction.replace(R.id.main_container, new ShopFragment());
                        fragmentTransaction.commit();
                        getSupportActionBar().setTitle("Shop");
                        item.setCheckable(true);
                        drawerLayout.closeDrawers();
                        break;
                    case R.id.nav_news:
                        fragmentTransaction = getSupportFragmentManager().beginTransaction();
                        fragmentTransaction.replace(R.id.main_container, new NewsFragment());
                        fragmentTransaction.commit();
                        getSupportActionBar().setTitle("News");
                        item.setCheckable(true);
                        drawerLayout.closeDrawers();
                        break;
                    case R.id.nav_media:
                        intent = new Intent(MainActivity.this, media_main.class);
                        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                        MainActivity.this.startActivity(intent);
                        break;
                    case R.id.nav_results:
                        fragmentTransaction = getSupportFragmentManager().beginTransaction();
                        fragmentTransaction.replace(R.id.main_container, new ResultsFragment());
                        fragmentTransaction.commit();
                        getSupportActionBar().setTitle("Results");
                        item.setCheckable(true);
                        drawerLayout.closeDrawers();
                        break;

                }


                return false;
            }

        });

    }

    @Override
    protected void onPostCreate(@Nullable Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        actionBarDrawerToggle.syncState();
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.drawer_menu, menu);
        return true;



    }
}

Answer 1

我遇到了同样的问题，但是当我从 v4.app.Fragment 类扩展时。而不是 android.app.Fragment，它工作正常，没有崩溃。

另见 this它提供了一些您可以尝试的解决方案。