活动状态<br>
暂停状态<br>
不位于栈顶，但是仍可见，例如对话框，透明的activiy<br>
停止状态<br>
不位于栈顶，不可见，需要内存时可能会被回收<br>
体验生命周期
启动第一个activity<br>
2019-12-02 22:47:57.316 10447-10447/com.yx.jjzg D/yaoixin: 1onCreate<br>2019-12-02 22:47:57.321 10447-10447/com.yx.jjzg D/yaoixin: 1onStart<br>2019-12-02 22:47:57.328 10447-10447/com.yx.jjzg D/yaoixin: 1onResume
跳转第二个activity<br>
2019-12-02 22:48:11.853 10447-10447/com.yx.jjzg D/yaoixin: 1onPause<br>2019-12-02 22:48:11.935 10447-10447/com.yx.jjzg D/yaoixin: 2onCreate<br>2019-12-02 22:48:11.937 10447-10447/com.yx.jjzg D/yaoixin: 2onStart<br>2019-12-02 22:48:11.942 10447-10447/com.yx.jjzg D/yaoixin: 2onResume<br>2019-12-02 22:48:12.202 10447-10447/com.yx.jjzg D/yaoixin: 1onStop
从activity返回到桌面<br>
2019-12-02 22:48:36.371 10447-10447/com.yx.jjzg D/yaoixin: 2onPause<br>2019-12-02 22:48:36.772 10447-10447/com.yx.jjzg D/yaoixin: 2onStop<br>
从桌面返回activty<br>
2019-12-02 22:48:49.693 10447-10447/com.yx.jjzg D/yaoixin: 2onRestart<br>2019-12-02 22:48:49.698 10447-10447/com.yx.jjzg D/yaoixin: 2onStart<br>2019-12-02 22:48:49.700 10447-10447/com.yx.jjzg D/yaoixin: 2onResume
返回第一个activity<br>
2019-12-02 22:49:03.704 10447-10447/com.yx.jjzg D/yaoixin: 2onPause<br>2019-12-02 22:49:03.774 10447-10447/com.yx.jjzg D/yaoixin: 1onRestart<br>2019-12-02 22:49:03.775 10447-10447/com.yx.jjzg D/yaoixin: 1onStart<br>2019-12-02 22:49:03.776 10447-10447/com.yx.jjzg D/yaoixin: 1onResume<br>2019-12-02 22:49:04.026 10447-10447/com.yx.jjzg D/yaoixin: 2onStop<br>2019-12-02 22:49:04.027 10447-10447/com.yx.jjzg D/yaoixin: 2onDestroy
第一个activity退出<br>
2019-12-02 22:49:23.910 10447-10447/com.yx.jjzg D/yaoixin: 1onPause<br>2019-12-02 22:49:23.988 10447-10447/com.yx.jjzg D/yaoixin: 1onStop<br>2019-12-02 22:49:25.060 10447-10447/com.yx.jjzg D/yaoixin: 1onDestroy
保存数据onSaveInstanceState<br>
活动被系统回收，要重新onCreate方法
