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Android开发之Service与IntentService的区别与使用场景(源代码剖析)
2014-04-08 11:39:02         来源:Android开发之Service与IntentService的区别与使用场景(源代码剖析)  
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因为最大部分的service不需要同时处理多个请求(处理多个请求是一个比较危险的多线程的场景),这样在在这种情况下呢,最好使用IntentService类如果你实现你的服务。

使用intentService与service有什么不同呢

(1)直接 创建一个默认的工作线程,该线程执行所有的intent传递给onStartCommand()区别于应用程序的主线程。

(2)直接创建一个工作队列,将一个意图传递给你onHandleIntent()的实现,所以我们就永远不必担心多线程。

(3)当请求完成后自己会调用stopSelf(),所以你就不用调用该方法了。

(4)提供的默认实现onBind()返回null,所以也不需要重写这个方法。so easy啊

(5)提供了一个默认实现onStartCommand(),将意图工作队列,然后发送到你onHandleIntent()实现。真是太方便了

我们需要做的就是实现onHandlerIntent()方法,还有一点就是经常被遗忘的,构造函数是必需的,而且必须调用超IntentService(字符串) ,因为工作线程的构造函数必须使用一个名称。如何实现呢,我们借助于谷歌官方文档来看一下吧。

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) {
              }
          }
      }
  }
}

那么它为什么不用stopself()方法呢,我们看一下自身的源代码把

public abstract class IntentService extends Service {
    private volatile Looper mServiceLooper;
    private volatile ServiceHandler mServiceHandler;
    private String mName;
    private boolean mRedelivery;

    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }
    }

    /**
     * Creates an IntentService.  Invoked by your subclass's constructor.
     *
     * @param name Used to name the worker thread, important only for debugging.
     */
    public IntentService(String name) {
        super();
        mName = name;
    }

    /**
     * Sets intent redelivery preferences.  Usually called from the constructor
     * with your preferred semantics.
     *
     * 

If enabled is true, * {@link #onStartCommand(Intent, int, int)} will return * {@link Service#START_REDELIVER_INTENT}, so if this process dies before * {@link #onHandleIntent(Intent)} returns, the process will be restarted * and the intent redelivered. If multiple Intents have been sent, only * the most recent one is guaranteed to be redelivered. * *

If enabled is false (the default), * {@link #onStartCommand(Intent, int, int)} will return * {@link Service#START_NOT_STICKY}, and if the process dies, the Intent * dies along with it. */ public void setIntentRedelivery(boolean enabled) { mRedelivery = enabled; } @Override public void onCreate() { // TODO: It would be nice to have an option to hold a partial wakelock // during processing, and to have a static startService(Context, Intent) // method that would launch the service & hand off a wakelock. super.onCreate(); HandlerThread thread = new HandlerThread("IntentService[" + mName + "]"); thread.start(); mServiceLooper = thread.getLooper(); mServiceHandler = new ServiceHandler(mServiceLooper); } @Override public void onStart(Intent intent, int startId) { Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); } /** * You should not override this method for your IntentService. Instead, * override {@link #onHandleIntent}, which the system calls when the IntentService * receives a start request. * @see android.app.Service#onStartCommand */ @Override public int onStartCommand(Intent intent, int flags, int startId) { onStart(intent, startId); return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY; } @Override public void onDestroy() { mServiceLooper.quit(); } /** * Unless you provide binding for your service, you don't need to implement this * method, because the default implementation returns null. * @see android.app.Service#onBind */ @Override public IBinder onBind(Intent intent) { return null; } /** * This method is invoked on the worker thread with a request to process. * Only one Intent is processed at a time, but the processing happens on a * worker thread that runs independently from other application logic. * So, if this code takes a long time, it will hold up other requests to * the same IntentService, but it will not hold up anything else. * When all requests have been handled, the IntentService stops itself, * so you should not call {@link #stopSelf}. * * @param intent The value passed to {@link * android.content.Context#startService(Intent)}. */ protected abstract void onHandleIntent(Intent intent); }

我们可以看到源代码里头的第15行handlerMessage方法里当处理完请求后就会调用stopself()方法了,外界就不用调用了,此外还有一点我们可以看到代码最后一行第110行,onhandleIntent()是一个抽象类,而其他类都是抽象类,所以我们就可以理解为什么只需要重写onhandleIntent()方法了吧。

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