Android开发之Service与IntentService的区别与使用场景(源代码剖析)
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.
- *
- * <p>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.
- *
- * <p>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。