android Service

默认UI线程

生命周期

onCreate() 创建
调用startService()或bindService()而该Service未创建
onStartCommand() 启动
调用startService()

多次请求开启service会导致相应的多次调用service的onStartCommand()。然而，只需要一次停止service（使用stopSelf() 或 stopService()）请求就可以停止它
- START_NOT_STICKY
  如果系统在onStartCommand()返回后杀死了service，系统不会重新创建service，除非传递的是挂起的intent。这是一个安全的选项避免运行你的service当没必要并且当你的应用程序可以重启所有未完成的任务。
- START_STICKY
  如果系统在onStartCommand()返回后杀死了service，系统会重新创建service并且调用onStartCommand()，但不会重新分发最后的intent。而是系统会使用一个null的intent调用onStartCommand()，除非这是被挂起的intent启动的service，这种情况下，这些intent会被传递。这适用于媒体播放器（或相似的service）不是执行命令，但无限的运行并且等待一个任务。
- START_REDELIVER_INTENT
  如果系统在onStartCommand()返回后杀死了service，系统会重新创建service并且用分发到service的最后的intent调用onStartCommand()。所有被挂起的intent都会被依次传递。这适用于一个service正在执行一个应该立即被恢复的任务，例如下载一个文件。
onBind() 绑定
调用bindService()
onDestroy()
调用stopService()和相应次数unbindService()
自身调用stopSelf()

IntentService 单线程执行 onHandleIntent()

创建一个默认的工作线程执行所有从主线程分发到onStartCommand()的intent
创建一个工作队列每次仅通过一个intent到达onHandleIntent()
所有请求处理完成后自动停止service
提供一个默认onBind()的实现返回null
提供一个默认onStartCommand()的实现发送intent到工作队列然后发送到onHandleIntent()
如果重写其它的方法，例如onCreate(), onStartCommand(), 或 onDestroy()，确保调用父类的实现

public class HelloService extends Service {
  private Looper mServiceLooper;
  private ServiceHandler mServiceHandler;

  // Handler that receives messages from the thread
  private final class ServiceHandler extends Handler {
      public ServiceHandler(Looper looper) {
          super(looper);
      }
      @Override
      public void handleMessage(Message msg) {
          // Normally we would do some work here, like download a file.
          // For our sample, we just sleep for 5 seconds.
          long endTime = System.currentTimeMillis() + 5*1000;
          while (System.currentTimeMillis() < endTime) {
              synchronized (this) {
                  try {
                      wait(endTime - System.currentTimeMillis());
                  } catch (Exception e) {
                  }
              }
          }
          // Stop the service using the startId, so that we don't stop
          // the service in the middle of handling another job
          stopSelf(msg.arg1);
      }
  }

  @Override
  public void onCreate() {
    // Start up the thread running the service.  Note that we create a
    // separate thread because the service normally runs in the process's
    // main thread, which we don't want to block.  We also make it
    // background priority so CPU-intensive work will not disrupt our UI.
    HandlerThread thread = new HandlerThread("ServiceStartArguments",
            Process.THREAD_PRIORITY_BACKGROUND);
    thread.start();

    // Get the HandlerThread's Looper and use it for our Handler
    mServiceLooper = thread.getLooper();
    mServiceHandler = new ServiceHandler(mServiceLooper);
  }

  @Override
  public int onStartCommand(Intent intent, int flags, int startId) {
      Toast.makeText(this, "service starting", Toast.LENGTH_SHORT).show();

      // For each start request, send a message to start a job and deliver the
      // start ID so we know which request we're stopping when we finish the job
      Message msg = mServiceHandler.obtainMessage();
      msg.arg1 = startId;
      mServiceHandler.sendMessage(msg);

      // If we get killed, after returning from here, restart
      return START_STICKY;
  }

  @Override
  public IBinder onBind(Intent intent) {
      // We don't provide binding, so return null
      return null;
  }

  @Override
  public void onDestroy() {
    Toast.makeText(this, "service done", Toast.LENGTH_SHORT).show();
  }
}

绑定通信

Binder内部类定义被activity调用的方法
onBind 返回Binder
ServiceConnection onServiceConnected()绑定时调用,传入返回的Binder

public class MyService extends Service {  
  
    private MyBinder mBinder = new MyBinder();  
  
    @Override  
    public void onCreate() {  
        super.onCreate();  
    }  
  
    @Override  
    public int onStartCommand(Intent intent, int flags, int startId) {  
        return super.onStartCommand(intent, flags, startId);  
    }  
  
    @Override  
    public void onDestroy() {  
        super.onDestroy();  
    }  
  
    @Override  
    public IBinder onBind(Intent intent) {  
        return mBinder;  
    }  
  
    class MyBinder extends Binder {  
  
        public void startDownload() {  
            Log.d("MyService", "startDownload() executed");  
            // 执行具体的下载任务  
        }  
  
    }  
  
}
       
public class MainActivity extends Activity{  
   
    private MyService.MyBinder myBinder;  
  
    private ServiceConnection connection = new ServiceConnection() { 
  
        @Override  
        public void onServiceConnected(ComponentName name, IBinder service) {  
            myBinder = (MyService.MyBinder) service;  
            myBinder.startDownload();  
        }  
        
        @Override  
        public void onServiceDisconnected(ComponentName name) {  
        }
    };  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState) { 
       
        Intent intent = new Intent(this, MyService.class);  
        //startService(intent);
        //stopService(intent); 
        bindService(intent, connection, BIND_AUTO_CREATE); 
        //unbindService(connection);
    }  
}

前台Service

public class MyService extends Service { 
  
    private MyBinder mBinder = new MyBinder();  
  
    @Override  
    public void onCreate() {  
        super.onCreate();  
        Notification notification = new Notification(R.drawable.ic_launcher,  
                "有通知到来", System.currentTimeMillis());  
        Intent notificationIntent = new Intent(this, MainActivity.class);  
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0,  
                notificationIntent, 0);  
        notification.setLatestEventInfo(this, "这是通知的标题", "这是通知的内容",  
                pendingIntent);  
        startForeground(1, notification);  
    }  
  
    .........  
  
}

给用户发送通知

一旦运行，service可以使用 Toast通知Toast Notifications）或状态条通知（Status Bar Notifications）通知用户事件。