Fragment中Android getSupportFragmentManager NULL指针异常

Question

点击抽屉导航项目后，我尝试使用 TabBar 和 View Pager 显示新 fragment 。

问题是新创建的 Fragment 导致 NULL 指针异常

viewPager.setAdapter(mAdapter);

我在 Fragment 中卡在带有标签的滑动 View 上几个小时，但没有运气，有人可以帮我解决这个问题吗？

对于可滑动的 View ，我遵循了本教程:

http://www.androidhive.info/2013/10/android-tab-layout-with-swipeable-views-1/

fragment 代码在这里:

import android.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import eu.com.mycompany.adapter.TabsPagerAdapter;

public class Fragment_AboutApplication extends Fragment implements ActionBar.TabListener {

    public Fragment_AboutApplication(){}
    private ViewPager viewPager;
    private TabsPagerAdapter mAdapter;
    private ActionBar actionBar;
    // Tab titles
    private String[] tabs = { "Top Rated", "Games", "Movies" };

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_about_app, container, false);


        // Initilization
        viewPager = (ViewPager) getActivity().findViewById(R.id.pager);
        actionBar = getActivity().getActionBar();
        mAdapter = new TabsPagerAdapter(getActivity().getSupportFragmentManager());

        /*HERE IS THROWED NULL POINTER EXCEPTION*/ 
        viewPager.setAdapter(mAdapter);
        actionBar.setHomeButtonEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        // Adding Tabs
        for (String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name)
                    .setTabListener(this));
        }
        return rootView;
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }
}

类 TabPagerAdapter:

public class TabsPagerAdapter extends FragmentPagerAdapter {

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

    @Override
    public Fragment getItem(int index) {

        switch (index) {
            case 0:
                // Top Rated fragment activity
                return new Fragment_TopRated();
            case 1:
                // Games fragment activity
                return new Fragment_TopRated();
            case 2:
                // Movies fragment activity
                return new Fragment_TopRated();
        }

        return null;
    }

    @Override
    public int getCount() {
        // get item count - equal to number of tabs
        return 3;
    }

}

View Pager 的主 fragment 布局

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v4.view.ViewPager>

    <TextView
        android:id="@+id/txtLabel"
         android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textSize="16dp"
        android:text="Settings"/>

    <ImageView android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/txtLabel"
        android:src="@drawable/ic_communities"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"/>    

</RelativeLayout>

异常(exception)是:

E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1504)
                at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:942)
                at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1121)
                at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
                at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1484)
                at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:450)
                at android.os.Handler.handleCallback(Handler.java:725)
                at android.os.Handler.dispatchMessage(Handler.java:92)
                at android.os.Looper.loop(Looper.java:153)
                at android.app.ActivityThread.main(ActivityThread.java:5330)
                at java.lang.reflect.Method.invokeNative(Native Method)
                at java.lang.reflect.Method.invoke(Method.java:511)
                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:608)
                at dalvik.system.NativeStart.main(Native Method)

Answer 1

改变:

mAdapter = new TabsPagerAdapter(getActivity().getSupportFragmentManager())

到:

 mAdapter = new TabsPagerAdapter(getChildFragmentManager())

当您在另一个 fragment 中使用 fragment 时，您必须使用 ChildFragmentManager 而不是 FragmentManager。