android开发笔记之service(一)

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前面的话

曾经去一个高大上的公司面试，面试官给我一支笔要我写一下service的生命周期。然后，我还真不会写，虽然说经常用service，但是还真说不清service的生命周期。然后就让人见笑了，最后自己也笑了。
今天，我们来详细的看看service的介绍

service简介

service的官方介绍：

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. Services can be started with Context.startService() and Context.bindService().

service是一个应用组件，主要设计是为了在后台进行一些长时间的操作。我们可以使用Context.startService() 和 Context.bindService()来启动service.

service，process与thread的关系：

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process. service与应用是在同一个process.
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thread. 但是service与main thread是同一个thread.
- Thread 是程序执行的最小单元，它是分配CPU的基本单位。可以用 Thread 来执行一些异步的操作
- Service 是android的一种机制，当它运行的时候如果是Local Service，那么对应的 Service 是运行在主进程的 main 线程上的。如：onCreate，onStart 这些函数在被系统调用的时候都是在主进程的 main 线程上运行的。如果是Remote Service，那么对应的 Service 则是运行在独立进程的 main 线程上。因此请不要把 Service 理解成线程，它跟线程半毛钱的关系都没有！
- 我们可以把Service 想象成一种消息服务，在任何有 Context 的地方调用 Context.startService、Context.stopService、 Context.bindService，Context.unbindService来控制它，也可以在 Service 里注册 BroadcastReceiver，在其他地方通过发送 broadcast 来控制它，但是这些都是 Thread 做不到的。

Service Lifecycle

Conte;xt.startService()启动服务， Context.stopService() or stopSelf()结束服务的生命周期
onCreate—–onStartCommand—– onStart—-(服务已经启动)—-(调用Context.stopService() or stopSelf()结束service)—-onDestroy
但是当service如果已经启动，我们再调用Conte;xt.startService()启动服务，则是再调用onStartCommand——onStart，而不再是调用onCreate方法。
Context.bindService()启动服务，Context.unbindService结束服务的生命周期：
onCreate—–onBind—（服务已经启动）——-（Context.unbindService结束service）—– onUnbind—— onDestroy

service生命周期的简图：

这里写图片描述

service 启动之后再bind的生命周期：
我们调用Conte;xt.startService()启动服务，再调用Context.bindService()绑定服务，然后再调用Context.unbindService解除绑定，再调用Context.stopService() 或者 stopSelf()结束服务。

onCreate—–>onStartCommand—–>onStart—–>onBind—–>onUnbind—–>onDestroy

下图是一个更详细的生命周期图：
这里写图片描述

常用service样例

自定义service

import android.app.Service;import android.content.Intent;import android.media.MediaPlayer;import android.os.Binder;import android.os.IBinder;import android.util.Log;public class DemoService extends Service{    public static final String TAG ="DemoService";    public MediaPlayer mediaPlayer;    @Override    public void onCreate() {        // TODO Auto-generated method stub        super.onCreate();        Log.i(TAG, "onCreate");        if(mediaPlayer == null){            mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.nx);            mediaPlayer.start();        }           }    @Override    public int onStartCommand(Intent intent, int flags, int startId) {        // TODO Auto-generated method stub        Log.i(TAG, "onStartCommand");        return super.onStartCommand(intent, flags, startId);    }    @Override    @Deprecated    public void onStart(Intent intent, int startId) {        // TODO Auto-generated method stub        super.onStart(intent, startId);        Log.i(TAG, "onStart");    }    @Override    public IBinder onBind(Intent arg0) {        // TODO Auto-generated method stub        Log.i(TAG, "onBind");        if(mediaPlayer == null){            mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.nx);        }        return null;    }    @Override    public boolean onUnbind(Intent intent) {        // TODO Auto-generated method stub        Log.i(TAG, "onUnbind");        return super.onUnbind(intent);    }    @Override    public void onRebind(Intent intent) {        // TODO Auto-generated method stub        super.onRebind(intent);        Log.i(TAG, "onRebind");    }    @Override    public void onDestroy() {        // TODO Auto-generated method stub        super.onDestroy();        Log.i(TAG, "onDestroy");        if(mediaPlayer != null){            mediaPlayer.stop();            mediaPlayer.release();        }    }    public class DemoServiceBinder extends Binder {          DemoService getService() {              return DemoService.this;          }      } }

在AndroidManifest.xml申明service

        <service android:name=".DemoService">              <intent-filter>                  <action android:name="com.example.DemoService" />              </intent-filter>          </service>

启动结束service

import android.os.Bundle;import android.os.IBinder;import android.app.Activity;import android.app.Service;import android.content.ComponentName;import android.content.Intent;import android.content.ServiceConnection;import android.util.Log;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class ServiceDemoMainActivity extends Activity implements OnClickListener{    //public static final String TAG = "ServiceDemoMainActivity";    public static final String TAG = "DemoService";    private Button myButton01;    private Button myButton02;    private Button myButton03;    private Button myButton04;    protected DemoService  myService;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_service_demo_main);        init();    }    private void init() {        // TODO Auto-generated method stub              myButton01 = (Button)findViewById(R.id.myButton01);        myButton01.setOnClickListener(this);        myButton02 = (Button)findViewById(R.id.myButton02);        myButton02.setOnClickListener(this);        myButton03 = (Button)findViewById(R.id.myButton03);        myButton03.setOnClickListener(this);        myButton04 = (Button)findViewById(R.id.myButton04);        myButton04.setOnClickListener(this);    }    @Override    public void onClick(View view) {        // TODO Auto-generated method stub        Intent intent = new Intent();          intent.setClass(ServiceDemoMainActivity.this, DemoService.class);          switch(view.getId()){            case R.id.myButton01:                startService(intent);                  break;            case R.id.myButton02:                stopService(intent);                  break;                   case R.id.myButton03:                bindService(intent, serviceConnection, Service.BIND_AUTO_CREATE);                   break;            case R.id.myButton04:                try {                    unbindService(serviceConnection);                  } catch (Exception e) {                    // TODO: handle exception                    Log.e(TAG,"e:"+e.toString());                }                break;        }            }    private ServiceConnection serviceConnection = new ServiceConnection() {         @Override          public void onServiceConnected(ComponentName name, IBinder service) {              Log.i(TAG, "service connect success");              myService = ((DemoService.DemoServiceBinder) service).getService();          }          @Override          public void onServiceDisconnected(ComponentName name) {              Log.i(TAG, "service disconnected");              myService = null;          }      };  }

参考资料

Android Service的生命周期
http://www.cnblogs.com/mengdd/archive/2013/03/24/2979944.html
Activity和Service的生命周期
http://www.cnblogs.com/andriod-html5/archive/2012/04/17/2539687.html

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