使用Fragment需要熟悉幾個類，包括FragmentActivity、FragmentManager、 FragmentTranscation，一個FragmentActivity可以包含多個Fragment，誰來管理？

FragmentManager就起到了作用。做Fragment的增加、刪除、替換的時候，事務FragmentTranslation 來負責執(zhí)行。

getFragmentManager()和getSupportFragmentManager()的區(qū)別很容易理解，android的v4擴展包中的FragmentActivity中獲取FragmentManager使用的就是getSupportFragmentManager()，android.app中獲取管理類的方法就是getFragmentManager()。

getChildFragmentManager() 屬于 android.support.v4.app.Fragment

    /**
    * Return a private FragmentManager for placing and managing Fragments
    * inside of this Fragment.
    */
   @NonNull
   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;
   }



  

getFragmentManager()在Activity中也在 android.support.v4.app.Fragment

 public FragmentManager getFragmentManager() {
        return mFragments.getFragmentManager();
    }
    // android.support.v4.app.Fragment 中
    @Nullable
    final public FragmentManager getFragmentManager() {
        return mFragmentManager;
    }

getSupportFragmentManager() 在 android.support.v4.app.FragmentActivity

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