Fragment中嵌套ViewPager数据空白页异常问题分析

         开题思考：Fragment放ViewPager，ViewPager里面是fragment。第一次进入没问题，再次进入ViewPager的fragment时里面内容就没了,出现数据空白页异常问题。

          描述：activity中放了两个Fragment，分别为待审核页、已加入页；其中待审核fragment中利用viewpager放了三个fragment，分别为全部、审核加入、审核退出，第二次切换待审核、已加入fragment时，会发现待审核fragment中ViewPager承载的Fragment会出现数据空白页现象。如下图所示：

         根据经验感觉是FragmentManager出了问题，因为FragmentManager的职责本来就是负责管理Fragment，包括对Fragment栈中的Fragement进行添加，删除，替换等操作，那既然出现了空白页，肯定是FragmentManager在进行Fragment替换时没有正常工作，查看Fragment以及FragmentActivity的源码发现有三种类型的FragmentManager，分别为getFragmentManager、getSupportFragmentManager、getChildFragmentManager；其中getFragmentManager跟getChildFragmentManager在Fragment类中，而getSupportFragmentManager位于FragmentActivity中，而getFragmentManager虽然在Fragment中，但是官方注释中最后有提到，如果当前Fragment是另外一个Fragment的子类，则当前FragmentManager属于父类，这就意味着，三者虽然相似但管理的对象却是不同的。

三者源码如下：

getFragmentManager:

    /**
     * Return the FragmentManager for interacting with fragments associated
     * with this fragment's activity.  Note that this will be non-null slightly
     * before {@link #getActivity()}, during the time from when the fragment is
     * placed in a {@link FragmentTransaction} until it is committed and
     * attached to its activity.
     *
     * <p>If this Fragment is a child of another Fragment, the FragmentManager
     * returned here will be the parent's {@link #getChildFragmentManager()}.
     */
    final public FragmentManager getFragmentManager() {
        return mFragmentManager;
    }

getSupportFragmentManager:

    /**
     * Return the FragmentManager for interacting with fragments associated
     * with this activity.
     */
    public FragmentManager getSupportFragmentManager() {
        return mFragments.getSupportFragmentManager();
    }

getChildFragmentManager:

    /**
     * Return a private FragmentManager for placing and managing Fragments
     * inside of this Fragment.
     */
    final public FragmentManager getChildFragmentManager() {
        if (mChildFragmentManager == null) {
            instantiateChildFragmentManager();
            if (mState >= RESUMED) {
                mChildFragmentManager.dispatchResume();
            } else if (mState >= STARTED) {
                mChildFragmentManager.dispatchStart();
            } else if (mState >= ACTIVITY_CREATED) {
                mChildFragmentManager.dispatchActivityCreated();
            } else if (mState >= CREATED) {
                mChildFragmentManager.dispatchCreate();
            }
        }
        return mChildFragmentManager;
    }

       根据google官方的描述（PS：English自译拿不出手），大意为getFragmentManager、跟getSupportFragmentManager是为了获取能管理和当前Activity有关联的Fragment的FragmentManager，也就是说此二者是属于Activity的，再来看下getChildFragment的官方注释

    /**
     * Return a private FragmentManager for placing and managing Fragments
     * inside of this Fragment.
     */
    final public FragmentManager getChildFragmentManager() {
   

文章开题提到的给ViewPager设置Adapter：

 viewPager.setAdapter(new ManageFragmentPagerAdapter(getFragmentManager(), list));

 viewPager.setAdapter(new ManageFragmentPagerAdapter(getChildFragmentManager(), list));