ViewPager嵌套带ViewPager的Banner，来回切换Banner数据丢失

数据丢失解决方法:
其实是Fragment嵌套了Fragment的问题，外层的Fragment是调用

NewMainPagerAdapter adapter = new NewMainPagerAdapter(getFragmentManager(), viewpagerFragmentList, mTitles);

而内层是要调用

BannerPagerAdapter mBannerPagerAdapter = new BannerPagerAdapter(fragment, mNewsMain.banners);

public BannerPagerAdapter(Fragment fm, List<NewsMain.Banner> banner) {

super(fm.getChildFragmentManager());

mBanner = banner;

}

修改完成后数据不会丢失了，但是来回切换几下，又会crash，报错如下

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime: FATAL EXCEPTION: main

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime: java.lang.NullPointerException

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.FragmentState.instantiate(Fragment.java:94)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1747)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.Fragment.performCreate(Fragment.java:1684)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:854)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.BackStackRecord.run(BackStackRecord.java:682)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:474)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.v13.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:167)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.v4.view.ViewPager.populate(ViewPager.java:1105)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:551)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:513)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:494)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.design.widget.TabLayout$ViewPagerOnTabSelectedListener.onTabSelected(TabLayout.java:1584)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.design.widget.TabLayout.selectTab(TabLayout.java:807)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.design.widget.TabLayout.selectTab(TabLayout.java:779)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.design.widget.TabLayout$Tab.select(TabLayout.java:1039)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.support.design.widget.TabLayout$1.onClick(TabLayout.java:620)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.view.View.performClick(View.java:4204)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.view.View$PerformClick.run(View.java:17355)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.os.Handler.handleCallback(Handler.java:725)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:92)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:137)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5041)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:511)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)

12-15 05:52:24.715 2976-2976/com.saidian.zuqiukong.debug E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method)

解决方法：

重写嵌套Fragment的onDetach方法（即调用了getChildFragmentManager()的Fragment）

@Override

public void onDetach() {

super.onDetach();

try {

Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");

childFragmentManager.setAccessible(true);

childFragmentManager.set(this, null);

} catch (NoSuchFieldException e) {

throw new RuntimeException(e);

} catch (IllegalAccessException e) {

throw new RuntimeException(e);

}

}