Android笔记 IntentService与Service的区别

Service 在官方API的描述为

A Service is an application component representing either an application's desire to perform a longer-running operation while not interacting with the user or to supply functionality for other applications to use. Each service class must have a corresponding <service> declaration in its package'sAndroidManifest.xml. Services can be started with Context.startService() and Context.bindService().

Note that services, like other application objects, run in the main thread of their hosting process. This means that, if your service is going to do any CPU intensive (such as MP3 playback) or blocking (such as networking) operations, it should spawn its own thread in which to do that work. More information on this can be found in Processes and Threads. The IntentService class is available as a standard implementation of Service that has its own thread where it schedules its work to be done.

主要用于后台服务 当应用程序被挂到后台的时候，为了保证应用某些组件仍然可以工作而引入了Service这个概念，那么这里面要强调的是Service不是独立的进程，也不是独立的线程，它是依赖于应用程序的主线程的，在更多时候不建议在Service中编写耗时的逻辑和操作，否则会引起ANR。这时需要引入IntentService，IntentService是继承Service的，那么它包含了Service的全部特性，当然也包含service的生命周期，那么与service不同的是，IntentService在执行onCreate操作的时候，内部开了一个线程，去执行你的耗时操作。

service提供了一个方法 onStartCommand 当service启动或被调用时候会执行这个方法。

onStartCommand(Intent intent, int flags, int startId)

Called by the system every time a client explicitly starts the service by calling startService(Intent), providing the arguments it supplied and a unique integer token representing the start request.

IntentService:异步处理服务，新开一个线程：handlerThread在线程中发消息，然后接受处理完成后，会清理线程，并且关掉服务。

IntentService有以下特点：

（1）  它创建了一个独立的工作线程来处理所有的通过onStartCommand()传递给服务的intents。

（2）  创建了一个工作队列，来逐个发送intent给onHandleIntent()。

（3）  不需要主动调用stopSelft()来结束服务。因为，在所有的intent被处理完后，系统会自动关闭服务。

（4）  默认实现的onBind()返回null

（5）  默认实现的onStartCommand()的目的是将intent插入到工作队列中