通常情况我们都是通过add方法来操作，这样导致容器里的层级比较多，显然效率比replace（只存在一个层级一个fragment）要低，取舍这个视情况而定。
1.通过add方法来添加fragment
每次add的过程其实就是在容器里添加fragment的过程，一般会把fragment添加到回退栈里，每次都会重新走生命周期，每个fragment都是独立的。
activity启动然后add fragment走的生命周期：
FragmentActivity: --------------onCreate
BlankFragmentOne: -----onAttach
-----onCreate
BlankFragmentOne: -----onCreateView
-----onActivityCreated
-----onStart
FragmentActivity: --------------onStart
FragmentActivity: --------------onResume
BlankFragmentOne: -----onResume
添加fragment
getActivity().getSupportFragmentManager().beginTransaction(）.add(rId, fragment, fragment.getClass().getSimpleName()).addToBackStack(fragment.getClass().getSimpleName()).commitAllowingStateLoss();
生命周期：BlankFragmentOne: -----onAttach -----onCreate -----onCreateView -----onActivityCreated -----onStart -----onResume
回退生命周期：
如果栈里面有fragment就pop没有说明只有activity直接finish
if (getActivity().getSupportFragmentManager().getBackStackEntryCount() >1) {
getActivity().getSupportFragmentManager().popBackStack();
} else{
getActivity().finish();
}
onPause -----onStop -----onDestroyView-----onDestroy
2.通过replace方法来添加fragment
从BlankFragmentOne通过replace方法添加fragment，每次都会先将之前的fragmen从容器里清掉，然后通过add方法添加到容器里
getActivity().getSupportFragmentManager().beginTransaction()
.replace(rId, fragment, fragment.getClass().getSimpleName())
.commitAllowingStateLoss();
BlankFragmentTwo: -----onAttach
BlankFragmentTwo: -----onCreate
BlankFragmentOne: -----onPause
BlankFragmentOne: -----onStop
-----onDestroyView
BlankFragmentOne: -----onDestroy
-----onDetach
BlankFragmentTwo: -----onCreateView
BlankFragmentTwo: -----onActivityCreated
3.viewpager里添加fragment
如下图：很清楚，activity先显示获取焦点，首先两个fragment都没显示setUserVisibleHint 都为false，然后BlankFragmentOne要显示，所以setUserVisibleHint为true，接着BlankFragmentOne显示走完生命周期，然后BlankFragmentTwo预加载走生命周期。
FragmentActivity: --------------onCreate
FragmentActivity: --------------onStart
FragmentActivity: --------------onResume
BlankFragmentOne: -----setUserVisibleHintfalse
BlankFragmentTwo: -----setUserVisibleHintfalse
BlankFragmentOne: -----setUserVisibleHinttrue
BlankFragmentOne: -----onAttach
-----onCreate
BlankFragmentTwo: -----onAttach
-----onCreate
BlankFragmentOne: -----onCreateView
BlankFragmentOne: -----onActivityCreated
-----onStart
-----onResume
BlankFragmentTwo: -----onCreateView
BlankFragmentTwo: -----onActivityCreated
BlankFragmentTwo: -----onStart
-----onResume
两个fragment滑动切换：只走setUserVisibleHint 显示为true，隐藏为false，其他生命周期无关,离开当前页面的时候会调onPause和onStop，返回的时候会调onStart和onResume。 如图：
网友评论