Service与 IntentService 的区别与使用场景（源代码剖析）
2014-05-26 08:41
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1）IntentService是继承自Service的
（2）1.Service不是一个单独的进程 ，它和应用程序在同一个进程中。
2.Service不是一个线程，所以我们应该避免在Service里面进行耗时的操作
（3）IntentService相对于Service来说，有几个非常有用的优点
IntentService使用队列的方式将请求的Intent加入队列，然后开启一个worker thread(线程)来处理队列中的Intent，对于异步的startService请求，IntentService会处理完成一个之后再处理第二个，每一个请求都会在一个单独的worker thread中处理，不会阻塞应用程序的主线程，这里就给我们提供了一个思路，如果有耗时的操作与其在Service里面开启新线程还不如使用IntentService来处理耗时操作。
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。
[java] view
plaincopy
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
[java] view
plaincopy
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。
（2）1.Service不是一个单独的进程 ，它和应用程序在同一个进程中。
2.Service不是一个线程，所以我们应该避免在Service里面进行耗时的操作
（3）IntentService相对于Service来说，有几个非常有用的优点
IntentService使用队列的方式将请求的Intent加入队列，然后开启一个worker thread(线程)来处理队列中的Intent，对于异步的startService请求，IntentService会处理完成一个之后再处理第二个，每一个请求都会在一个单独的worker thread中处理，不会阻塞应用程序的主线程，这里就给我们提供了一个思路，如果有耗时的操作与其在Service里面开启新线程还不如使用IntentService来处理耗时操作。
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。
[java] view
plaincopy
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
[java] view
plaincopy
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。
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