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() {
上文注释大致意思返回一个私有的FragmentManager来管理Fragment,它属于Fragment。至此整个问题就梳理清楚了,因为文章开题提出的问题,是在Fragment中使用ViewPager装载Fragment,也就是说,在Fragment中应该是用的是Fragemnt类中提供的manager方法,即在给ViewPager设置FragmentManager的时候应该使用getChildFragmentManager。
文章开题提到的给ViewPager设置Adapter:
viewPager.setAdapter(new ManageFragmentPagerAdapter(getFragmentManager(), list));
经过分析应该修改为:
viewPager.setAdapter(new ManageFragmentPagerAdapter(getChildFragmentManager(), list));
归纳总结 : getFragmentManager()所得到的是所在fragment 的父容器的管理器,而getChildFragmentManager()所得到的是在fragment 里面子容器的管理器,即getFragmentManager到的是activity对所包含fragment的Manager,而如果是fragment作为容器装载Fragment,就需要利用getChildFragmentManager()了