Android横竖屏切换时Activity的生命周期问题

在清单文件的activity节点有一个属性configChanges，横竖屏切换时Activity的生命周期就跟它的值有关。Android中横竖屏切换默认是会重新创建一个Activity的，如果为了使横竖屏切换时不重新创建Activity，那么就需要把configChanges的值指定为“orientation|keyboardHidden”，不过这个有个前提，就是targetSdkVersion必须小于等于12，否则还是会重新创建一个Activity，如果targetSdkVersion大于13，那么configChanges必须指定为“orientation|keyboardHidden|screenSize”,来自Google官网对orientation说明：

The screen orientation has changed — the user has rotated the device.
Note: If your application targets API level 13 or higher (as declared by the minSdkVersion and targetSdkVersion attributes), then you should also declare the “screenSize” configuration, because it also changes when a device switches between portrait and landscape orientations.

这个screenSize是在API13时添加的：

The current available screen size has changed. This represents a change in the currently available size, relative to the current aspect ratio, so will change when the user switches between landscape and portrait. However, if your application targets API level 12 or lower, then your activity always handles this configuration change itself (this configuration change does not restart your activity, even when running on an Android 3.2 or higher device).
Added in API level 13.

总结：
1.如果指定了横竖屏切换时不创建Activity，那么横竖屏切换只会回调onConfigurationChanged方法。
2.如果横竖屏切换时会重新创建Activity，那么其回调过程为：
旧的Activity：onPause–>onSaveInstanceState–>onStop–>onDestroy
新的Activity：onCreate–>onStart–>onRestoreInstanceState–>onResume

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