android开发笔记之service(一)

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：

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：

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

1. Android Service的生命周期
   http://www.cnblogs.com/mengdd/archive/2013/03/24/2979944.html

2. Activity和Service的生命周期
   http://www.cnblogs.com/andriod-html5/archive/2012/04/17/2539687.html