FragmentManager上的空对象引用

Question

此行mFragmentTransaction.replace(R.id.containerView,new SentFragment()).commit();

上出现空对象引用异常

以下代码正在尝试在TabActivity中添加Mainactivity。但是在TabFragment中它抛出了null异常。我知道，问题是我的TabFragment。以下是我的MainActivty.java，之后会有TabFragment.java

public class MainActivity extends AppCompatActivity {
DrawerLayout mDrawerLayout;
NavigationView mNavigationView;
FragmentManager mFragmentManager;
FragmentTransaction mFragmentTransaction;

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

    /**
     *Setup the DrawerLayout and NavigationView
     */

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
    mNavigationView = (NavigationView) findViewById(R.id.shitstuff);

    /**
     * Lets inflate the very first fragment
     * Here , we are inflating the TabFragment as the first Fragment
     */

    mFragmentManager = getSupportFragmentManager();
    mFragmentTransaction = mFragmentManager.beginTransaction();
    mFragmentTransaction.replace(R.id.containerView,new SentFragment()).commit();
    /**
     * Setup click events on the Navigation View Items.
     */

    mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(MenuItem menuItem) {
            mDrawerLayout.closeDrawers();



            if (menuItem.getItemId() == R.id.nav_item_sent) {
                FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.containerView,new SentFragment()).commit();

            }

            if (menuItem.getItemId() == R.id.nav_item_inbox) {
                FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
               // xfragmentTransaction.replace(R.id.containerView,new TabFragment()).commit();
            }

            return false;
        }

    });

    /**
     * Setup Drawer Toggle of the Toolbar
     */

    android.support.v7.widget.Toolbar toolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.toolbar);
    ActionBarDrawerToggle mDrawerToggle = new ActionBarDrawerToggle(this,mDrawerLayout, toolbar,R.string.app_name,
            R.string.app_name);

    mDrawerLayout.setDrawerListener(mDrawerToggle);

    mDrawerToggle.syncState();

}

}

TabFragment.java

public class TabFragment extends Fragment {

public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 3 ;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    /**
     *Inflate tab_layout and setup Views.
     */
    View x =  inflater.inflate(R.layout.tab_layout,null);
    tabLayout = (TabLayout) x.findViewById(R.id.tabs);
    viewPager = (ViewPager) x.findViewById(R.id.viewpager);

    /**
     *Set an Apater for the View Pager
     */
    viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));

    /**
     * Now , this is a workaround ,
     * The setupWithViewPager dose't works without the runnable .
     * Maybe a Support Library Bug .
     */

   tabLayout.post(new Runnable() {
        @Override
        public void run() {
            tabLayout.setupWithViewPager(viewPager);
        }
    });

    return x;

}

class MyAdapter extends FragmentPagerAdapter {

    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    /**
     * Return fragment with respect to Position .
     */

    @Override
    public Fragment getItem(int position)
    {
        switch (position){
            case 0 : return new PrimaryFragment();
           // case 1 : return new SocialFragment();
           // case 2 : return new UpdatesFragment();
        }
        return null;
    }

    @Override
    public int getCount() {

        return int_items;

    }

    /**
     * This method returns the title of the tab according to the position.
     */

    @Override
    public CharSequence getPageTitle(int position) {

        switch (position){
            case 0 :
                return "Primary";
            case 1 :
                return "Social";
            case 2 :
                return "Updates";
        }
        return null;
    }
}

}

请帮我纠正此代码。

我得到的错误就是这个。

tabproject E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.kpgames.tabproject, PID: 7410
java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference
    at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:418)
    at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:413)
    at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99)
    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:943)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1157)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1025)
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.view.View.measure(View.java:18788)
    at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1075)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
    at android.view.View.measure(View.java:18788)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
    at android.view.Choreographer.doCallbacks(Choreographer.java:670)
    at android.view.Choreographer.doFrame(Choreographer.java:606)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.refl

Answer 1

我将2个片段传递给我配置的3个Tabhost。这就是为什么我得到空问题。它的工作正常。