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Android面试中,你也许会被问到题目中的问题,这里我们基于以下几点来延伸解读其中原因:
1、什么是ANR?ANR发生的原因是什么?
2、Looper为什么要无限循环?
3、线程的几种状态
4、主线程中的Looper.loop()一直无限循环为什么不会造成ANR?
1、什么是ANR?ANR发生的原因是什么?
ANR即Application Not Responding,顾名思义就是应用程序无响应。
在Android中,一般情况下,四大组件均是工作在主线程中的,Android中的Activity Manager和Window
Manager会随时监控应用程序的响应情况,如果因为一些耗时操作(网络请求或者IO操作)造成主线程阻塞一定时间(例如造成5s内不能响应用户事件或者BroadcastReceiver的onReceive方法执行时间超过10s),那么系统就会显示ANR对话框提示用户对应的应用处于无响应状态。
简单总结就是以下两点:
1. 不要让主线程干耗时的工作
2. 不要让其他线程阻塞主线程的执行
2、Looper为什么要无限循环?
Looper中重要的两个方法为prepare()、loop()
prepare()源码
Looper在prepare中通过ThreadLocal保证了每个线程Loop