Activity 生命周期

系统：4.0.3

1.启动时：

onCreate ->onWindowAttributesChanged(多次) ->  onStart -> onResume -> onAttachedToWindow -> onWindowFocusChanged

2. 按后退键时：
onPause -> onWindowFocusChanged -> onStop -> onDestroy

3. 按Home键时：
onUserLeaveHint -> onPause -> onWindowFocusChanged -> onSaveInstanceState -> onStop 

4. 按Home键后返回程序
onRestart -> onStart -> onResume ->onWindowFocusChanged

4. 按电源键熄灭屏幕时：
onPause -> onWindowFocusChanged -> onSaveInstanceState -> onStop 

5. 按电源键重新点亮屏幕(不解锁)
onRestart -> onStart -> onResume
6. 解锁
onWindowFocusChanged