Android IntentService应用

IntentService应用

IntentService继承Service，但又不同于普通的Service。

Service是用于后台服务的，但它仍然在主线程中运行，耗时的逻辑和操作都不适合在Service中运行，IntentService弥补了这一缺点。

IntentService源码，

public abstract class IntentService extends Service {

    @Override
    public void onCreate() {
        super.onCreate();
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }
    @Override
    public void onStart(@Nullable Intent intent, int startId) {
        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);
    }   

    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
    }

    @Override
    public void onDestroy() {
        mServiceLooper.quit();
    }
}

在onCreeate()方法中，创建了一个HandlerThread线程，并初始化了一个ServiceHandler来传递消息。
在onStart()方法中，调用ServiceHandler的sendMessage()方法。

HandlerThread类

HandlerThread是一个线程类，并在内部创建了一个Looper来管理线程。

public class HandlerThread extends Thread {

    @Override
    public void run() {
        mTid = Process.myTid();
        Looper.prepare();
        synchronized (this) {
            mLooper = Looper.myLooper();
            notifyAll();
        }
        Process.setThreadPriority(mPriority);
        onLooperPrepared();
        Looper.loop();
        mTid = -1;
    }

    /**
     * This method returns the Looper associated with this thread. If this thread not been started
     * or for any reason isAlive() returns false, this method will return null. If this thread
     * has been started, this method will block until the looper has been initialized.  
     * @return The looper.
     */
    public Looper getLooper() {
        if (!isAlive()) {
            return null;
        }

        // If the thread has been started, wait until the looper has been created.
        synchronized (this) {
            while (isAlive() && mLooper == null) {
                try {
                    wait();
                } catch (InterruptedException e) {
                }
            }
        }
        return mLooper;
    }

}

ServiceHandler类

ServiceHandler继承了Handler类，设置了looper参数，所有的操作都会在该looper线程中进行，也就是在HandlerThread线程中进行。onHandleIntent()方法实现了回调。

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);
    }
}

创建IntentService

如果我们需要一个下载文件Service，DownloadService继承IntentService，只需要实现onHandleIntent()方法即可。

public class DownloadService extends IntentService {

    public DownloadService(String name) {
        super(name);
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) {

    }

}