关于getFragmentManager() 和 getChildFragmentManager() 两个方法

菜鸟第一次写博客，就拿在项目中遇到的问题来开篇吧

首先问题出现

一个activity里包含了一个fragment页面，一个fragment里有多个fragment，采用的技术是viewpager + fragment，第一次进入fragment加载都没问题，生命周期也都执行了。由于我的项目里该activity的launchMode是singleTask模式，当第二次进入该activity时，viewpager里的fragment加载就出问题了，生命周期都没执行。

问题解决

后来发现是getFragmentManager()和getChildFragmentManager() 两个方法的错误使用导致。

看下源码

/**
 * 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.
 *
 * 
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;
}

/**
 * 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;
}

 源码注释讲的很清楚getFragmentManager()获取到的管理器是针对fragment所依附的activity来讲，也就是在activity里管理一级子fragment所使用的，如果fragment里面还有fragment，就应该使用getChildFragmentManager() 方法，修改后确实问题解决了。