1.Activity生命周期
Activity的生命周期如下图所示:
正常启动的时候，Activity的启动流程如下:
- onCreate
- onStart
- onResume
其中onCreate负责处理程序初始化工作，如界面资源的初始化，数据初始化等。onStart表明Activity正在启动，此时Activity可见但不在前台，而onResume表示Activity在前台且可与用户进行交互（当在onResume加上延时后，发现第一次启动时onResume完成后，控件才显示出来）。
观察Activity的测试程序:
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01-29 21:59:58.681 22123 22123 D ActivityLifeCycle: onCreate
01-29 21:59:58.688 22123 22123 D ActivityLifeCycle: onStart
01-29 21:59:58.692 22123 22123 D ActivityLifeCycle: onResume
当按下返回键进入Launcher时或者锁屏时,进行如下流程:
- onPause
- onStop
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01-29 22:15:47.796 23071 23071 D ActivityLifeCycle: onPause
01-29 22:15:48.375 23071 23071 D ActivityLifeCycle: onStop
当再次点开该Activity时,不会再调用onCreate:
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01-30 09:52:10.554 31784 31784 D ActivityLifeCycle: onStart
01-30 09:52:10.556 31784 31784 D ActivityLifeCycle: onResume
当在该Activity跳转到别的Activity时:
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01-30 09:56:28.517 32182 32182 D ActivityLifeCycle: onPause
01-30 09:56:28.898 32182 32182 D ActivityLifeCycle: onStop
当返回到该Activity时:
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01-30 09:56:41.939 32182 32182 D ActivityLifeCycle: onStart
01-30 09:56:41.940 32182 32182 D ActivityLifeCycle: onResume
当屏幕进行旋转时，观察可得Activity会先销毁当前的Activity,在重新创建一个新的，并在onResume前，调用onRestoreInstance
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01-30 10:00:01.089 32483 32483 D ActivityLifeCycle: onPause
01-30 10:00:01.090 32483 32483 D ActivityLifeCycle: onStop
01-30 10:00:01.091 32483 32483 D ActivityLifeCycle: onDestroy
01-30 10:00:01.236 32483 32483 D ActivityLifeCycle: onCreate
01-30 10:00:01.241 32483 32483 D ActivityLifeCycle: onStart
01-30 10:00:01.242 32483 32483 D ActivityLifeCycle: onRestoreInstance
01-30 10:00:01.243 32483 32483 D ActivityLifeCycle: onResume
当AndroidManifest.xml中增添了android:configChanges="orientation|screenSize"后，则只会回调onConfigurationChanged:
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01-30 10:01:07.773 432 432 D ActivityLifeCycle: onConfigurationChanged
