Android应用程序四大组件之Service(一)

What is a Service?

Service是一个应用程序组件,可以用来处理一些比较耗时的操作.

•A Service is not a separate process. The Service object itself does not imply it is running in its own process; unless otherwise specified, it runs in the same process as the application it is part of.

Service不是一个单独的进程.

• A Service is not a thread. It is not a means itself to do work off of the main thread (to avoid Application Not Responding errors).

Service不是一个线程.

启动方法

1.Content.startService()

此启动方式,不会与绑定者没有关系,即使程序退出,servcie仍然运行着.

2.Content.bindService()

bindService会与绑定者销毁,即程序退出,service就立即停止.

Service Lifecycle

两种Service启动方式不同,生命周期也不一样.

1.startService

启动服务(在要与绑定的activity上添加这行代码)startService(new Intent(ServiceDemoActivity.this, MyService.class));

MyServcie.class

public class MyService extends Service{ @Override public IBinder onBind(Intent intent) { System.out.println("onBind()"); return myBinder; } @Override public void onCreate() { System.out.println("onCreate()"); super.onCreate(); } @Override public int onStartCommand(Intent intent, int flags, int startId) { System.out.println("intent:"+intent+"(flags):"+flags+"startId:"+startId); return super.onStartCommand(intent, flags, startId); } @Override public void onDestroy() { System.out.println("onDestroy()"); super.onDestroy(); } }

当我们启动Service时,响应的可以看到输出日志onCreate()->onStartCommand(); 多次startService并不会启动多个服务,onCreate()在创建时被调用,在Android系统1.x以前是并不是重写onStartCommand()而是onStart().onBind()在此启动方式并不会被调用.

//停住服务 (在要与绑定的activity上添加这行代码) stopService(new Intent(ServiceDemoActivity.this, MyService.class));

当我们停止Service时,响应的可以看到输出日志onDestroy().

2.bindService

(在要与绑定的activity上添加这行代码)此service与application处于同一进程时情况.通过bindService启动服务.

bindService(new Intent(ServiceDemoActivity.this,MyService.class), serconn, BIND_AUTO_CREATE);//需在onServiceConnected()从myservice中onBind()返回Ibinder对象,通过该对象取得相应的service实例 private ServiceConnection serconn = new ServiceConnection() { @Override public void onServiceDisconnected(ComponentName name) { System.out.println("onServiceDisconnected"); } @Override public void onServiceConnected(ComponentName name, IBinder service) { System.out.println("onServiceConnected"); myService = ((MyBinder)service).getService(); mTextView.setText("get from Service time::"+myService.getSystemTime()); } };

//在service类声明一个内部类继承Binder在该内部类中提供方法返回service实例.//在service类中声明这个内部的实例new MyBinder().以便onBind返回public class MyService extends Service{ private MyBinder myBinder = new MyBinder(); @Override public IBinder onBind(Intent intent) { System.out.println("onBind()"); return myBinder; } @Override public void onCreate() { System.out.println("onCreate()"); super.onCreate(); } @Override public int onStartCommand(Intent intent, int flags, int startId) { System.out.println("intent:"+intent+"(flags):"+flags+"startId:"+startId); return super.onStartCommand(intent, flags, startId); } @Override public void onDestroy() { System.out.println("onDestroy()"); super.onDestroy(); } @Override public boolean onUnbind(Intent intent) { System.out.println("onUnbind()"); return super.onUnbind(intent); } @Override public void onRebind(Intent intent) { System.out.println("onRebind()"); super.onRebind(intent); } public class MyBinder extends Binder{ MyService getService(){ return MyService.this; } } public String getSystemTime(){ return System.currentTimeMillis()+""; } } 当我启动服务时,可看见log输出onCreate()->onBind()->onServiceConnectedunbindService(serconn);当我们停止服务时,可看见log输出onUnbind()->onDestroy()