android 笔记（Service）

Service

 

 

一。Serivce的启动方式分两种 

 

1.startService。用这种方式启动的话，负责启动这个service的Activity或者其余组件即便被销毁了，Service也会继续在后台运行，必须得Serivce本身作完任务区去调用stopSelf或者stopService去中止这个Serice。这种方式是Start方式

 

2.bindService。这种方式要组件去调用BindService去绑定一个Service，这种方式Service的生命周期是知道全部绑定这个service的组件unbind以后才会销毁。这种方式称之为 Bound

 

 

startService调用后会自动调用startCommand，你须要作的工做能够在这里写，例如启动新线程去执行任务之类的。

bindService以后会调用Onbind函数，功能同上，须要本身去重写，还有就是通讯就是经过这个onbind函数返回的IBinder。

以上两种方式能够一块儿使用，不是必定要分开。。

 

 

 

二．实现Service须要重写的方法

通常来讲，实现Service，实现如下几个方法就好：

 

onStartCommand()

onBind()

onCreate()

onDestroy()

函数名字仍是很是清楚的，具体做用就不说了。

 

三．在manifest里面加入Service

 

跟Activity同样，要使用你本身写的Service，必须得在manifest里面注册

例如

<manifest ... >
  ...
  <application ... >
      <service android:name=".ExampleService" />
      ...
  </application>
</manifest>

 

Service的名字一旦肯定，就不要更改了，由于其余地方会利用这个名字去访问Service，

值得注意的是，一个service能够被其余应用程序去访问，若是你不想被其余应用程序访问，就在文件里面加入属性android:exported，而后设置为False。

四．实现Service的两种方法

实现Service主要有两种方式：

1.Service

要重写几个函数，并且通常工程来讲，都要本身建立新线程来执行任务，这些工做都要咱们本身去编写来作。

代码以下：

 

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(); 
  }
}

 

 

2.IntentService

若是只是启动一个线程作一个单独任务，这个是首选，系统帮你实现好了几个必须重写的函数，你只须要作的是事情就是实现一个函数就行：onHandleIntent(intent) 参数是startCommand那里传过来的。

看代码：

public class HelloIntentService extends IntentService {

  /** 
   * A constructor is required, and must call the super IntentService(String)
   * constructor with a name for the worker thread.
   */
  public HelloIntentService() {
      super("HelloIntentService");
  }

  /**
   * The IntentService calls this method from the default worker thread with
   * the intent that started the service. When this method returns, IntentService
   * stops the service, as appropriate.
   */
  @Override
  protected void onHandleIntent(Intent intent) {
      // 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) {
              }
          }
      }
  }
}

注意，startCommand返回的值是有用的，决定这个service被系统干掉后要不要从新启动，这个值有三个枚举START_NOT_STICKY，START_STICKY，START_REDELIVER_INTENT

五．经过intent来开启Service

启动Service就是建立一个intent对象，参数传进去须要启动的Service名称，就能够啦，调用startService啦，

若是须要Service传回来一些消息，能够 用PendingIntent，而后传给startService用的intent，而后能够用getBroadcast来获得消息。 

六．startForeground()来让service在前端显示

相似播放器同样，你想通知栏里面看到在放什么歌曲，还有点击放下一首时，须要调用startForeground()让service运行在前端

 

Notification notification = new Notification(R.drawable.icon, getText(R.string.ticker_text),
        System.currentTimeMillis());
Intent notificationIntent = new Intent(this, ExampleActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
notification.setLatestEventInfo(this, getText(R.string.notification_title),
        getText(R.string.notification_message), pendingIntent);
startForeground(ONGOING_NOTIFICATION_ID, notification);

 

具体Service的其余方面能够去看下官方文档