用手机做了实验，结果如下:

竖屏切横屏会调用完整的生命周期:

03-09 17:08:35.170: I/MainActivity(14086): MainActivity Paused

03-09 17:08:35.200: I/MainActivity(14086): MainActivity Stopped

03-09 17:08:35.200: I/MainActivity(14086): MainActivity Destroyed

03-09 17:08:35.320: I/MainActivity(14086): MainActivity Created!

03-09 17:08:35.320: I/MainActivity(14086): MainActivity Started

03-09 17:08:35.320: I/MainActivity(14086): MainActivity Resumed

横屏切竖屏也会调用完整的生命周期:

03-09 17:11:20.980: I/MainActivity(14287): MainActivity Paused

03-09 17:11:21.030: I/MainActivity(14287): MainActivity Stopped

03-09 17:11:21.030: I/MainActivity(14287): MainActivity Destroyed

03-09 17:11:21.280: I/MainActivity(14287): MainActivity Created!

03-09 17:11:21.280: I/MainActivity(14287): MainActivity Started

03-09 17:11:21.280: I/MainActivity(14287): MainActivity Resumed

按手机开关键时，屏幕锁屏，Activity会调用:

03-09 17:13:54.170: I/MainActivity(14576): MainActivity Paused

03-09 17:13:54.220: I/MainActivity(14576): MainActivity Stopped

重新进入手机以后:

03-09 17:14:02.530: I/MainActivity(14576): MainActivity Restarted

03-09 17:14:02.530: I/MainActivity(14576): MainActivity Started

03-09 17:14:02.580: I/MainActivity(14576): MainActivity Resumed

按Home键:

03-10 14:04:00.600: I/MainActivity(10540): MainActivity Paused

03-10 14:04:01.110: I/MainActivity(10540): MainActivity Stopped

重新启动程序:

03-10 14:04:05.370: I/MainActivity(10540): MainActivity Restarted

03-10 14:04:05.370: I/MainActivity(10540): MainActivity Started

03-10 14:04:05.370: I/MainActivity(10540): MainActivity Resumed

按返回键:

03-10 14:42:58.440: I/MainActivity(13062): MainActivity Paused

03-10 14:42:58.930: I/MainActivity(13062): MainActivity Stopped

03-10 14:42:58.940: I/MainActivity(13062): MainActivity Destroyed

重新启动程序:

03-10 14:43:06.120: I/WelcomeActivity(13062): Welcome Activity Created

03-10 14:43:06.120: I/WelcomeActivity(13062): Welcome Activity Started

03-10 14:43:08.200: I/MainActivity(13062): MainActivity Created!

03-10 14:43:08.200: I/MainActivity(13062): MainActivity Started

03-10 14:43:08.200: I/MainActivity(13062): MainActivity Resumed

可见，按Home和按返回键的区别是: 按Home键Activity只是到了后台，并没有被销毁，而按返回键后Activity直接被销毁调用了onDestroy()

在Manifest文件中配置可以设置Activity的方向:

android:name=".MainActivity"

android:label="@string/app_name"

android:screenOrientation="portrait"

android:configChanges="orientation|keyboardHidden" >