Activity与Fragment的生命周期测试

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">

<fragment
android:name="com.cstar.androidstudy.FragPageOne"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1"
tools:layout="@layout/frag_page_1"/>

<fragment
android:name="com.cstar.androidstudy.FragPageTwo"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1"
tools:layout="@layout/frag_page_2" />
</LinearLayout>

一个Activity中放入2个Fragment，然后测试Activity和2个Fragment的生命周期

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onCreate

1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onAttach!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onCreate!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onCreateView!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onViewCreated!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onAttach
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onCreate!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onCreateView!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onViewCreated!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onStart!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onActivityCreated!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onActivityCreated!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onStart!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onStart!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onResume!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onResume!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onResume!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onPause!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onPause!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onPause!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onStop!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onStop!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onStop!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onRestart!
1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onStart!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onStart!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onStart!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onResume!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onResume!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onResume!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onPause!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onPause!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onPause!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onStop!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onStop!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onStop!

1169-1169/com.cstar.androidstudy D/fragment﹕ MainActivity.onDestroy!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onDestroyView!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onDestroy!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentOne.onDetach!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onDestroyView!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onDestroy!
1169-1169/com.cstar.androidstudy D/fragment﹕ FragmentTwo.onDetach!

注解：
1、主Activity onCreate后才开始依次初始化每个Fragment，每个Fragment先onAttach，然后onCreate，onCreateView，onViewCreated，这里值得注意的是，与Activity不同，Fragment的onCreate中，并没有创建、呈现子组件，所以在onCreate中，是无法访问子组件的。在onCreateView运行完成后，Fragment中才创建添加了子组件。所以至少要再onViewCreated中，才能用 fragment.getView().findViewById(R.id.xxx)获取子组件的引用。

2、主Activity中所有Fragment依次执行完onViewCreated之后，Activity才onStart开始显示界面。这时每个Fragment会调用onActivityCreated，仅仅在Activity初次onStart时，每个Fragment才会调用onActivityCreated，Activity以后再次调用onStart，Fragment不会再调用onActivityCreated（根据onActivityCreated的名称，这是可想而知的）。如果某个Fragment中的组件想访问其他Fragment中组件的数据，那么必须等到该Fragment调用onActivityCreated时，才能保证其他所有Fragment都已创建了子组件，在onActivityCreated之前，很可能会因为别的Fragment还没有初始化创建子组件而导致findViewById返回null。每个Fragment执行onActivityCreated后，会执行onStart。

3、主Activity分别执行onResume,onPause,onStop之后，每个Fragment也会跟着Activity之后依次执行同名的方法，即Activity.onResume——>Fragment1.onResume——>Fragment2.onResume……。但Fragment没有onRestart方法，主Activity重新回到栈顶显示界面，执行onRestart，onStart，每个Fragment依次执行onStart（没有onRestart）

4、主Activity退出时，Activity和每个Fragment依次执行onPause，onStop。最后主Activity调用onDestroy。每个Fragment依次调用onDestroyView，onDestroy，onDetach，注意Fragment最后的回调方法是onDetach而不是onDestroy