1.前言
想必大家應(yīng)該都使用過Service組件叁幢，為什么有service，還需要IntentService呢巍杈。它們有什么不同忧饭，帶著這些問題，下面我們分析下源碼筷畦。
2.IntentService源碼分析
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(@Nullable 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(@Nullable 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
@Nullable
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)}.
* This may be null if the service is being restarted after
* its process has gone away; see
* {@link android.app.Service#onStartCommand}
* for details.
*/
@WorkerThread
protected abstract void onHandleIntent(@Nullable Intent intent);
}
2.1 onCreate方法
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);
}
public class HandlerThread extends Thread
可以看出在onCreate方法中HandlerThread變量词裤。可以看出HandlerThread其實(shí)就是一個(gè)線程鳖宾。在此啟動(dòng)一個(gè)線程吼砂。同時(shí)定義一個(gè)ServiceHandler的Handler，由于接收處理onStart發(fā)出的Message鼎文。接下來看看onStartCommand&onStart方法渔肩。
2.2 onStartCommand和onStart方法
@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 onStart(@Nullable Intent intent, int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
}
在啟動(dòng)這個(gè)service的時(shí)候會(huì)調(diào)用onStartCommand方法，onStartCommand方法又會(huì)調(diào)用onStart方法拇惋，onStart干了什么事情呢周偎？其實(shí)就是發(fā)送Message給到ServiceHandler中。
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);
}
}
然后處理onHandlerIntent()這個(gè)抽象方法撑帖。onHandlerIntent方法跑在onCreate方法開啟的線程中蓉坎。然后stopSelf()。
2.3 onDestroy方法
@Override
public void onDestroy() {
mServiceLooper.quit();
}
服務(wù)停止后會(huì)執(zhí)行onDestroy方法胡嘿，在onDestroy方法中會(huì)清除消息隊(duì)列Message蛉艾。所以IntentService多次啟動(dòng)，如果服務(wù)停止了，會(huì)清除所有消息隊(duì)列的任務(wù),后面的任務(wù)不會(huì)執(zhí)行勿侯。因?yàn)槎寂茉谝粋€(gè)消息隊(duì)列中拓瞪，多次啟動(dòng)服務(wù)不會(huì)執(zhí)行onCreate方法，所以不會(huì)創(chuàng)建多個(gè)消息隊(duì)列罐监。
2.4 總結(jié)
由此可以看出Service和IntentService的區(qū)別
1.Service與IntentService本質(zhì)上是一個(gè)Service組件吴藻。
2.Service不能處理耗時(shí)過長的任務(wù)，會(huì)引起ANR, 因?yàn)閟ervice運(yùn)行在UI線程上弓柱。
3.Service需要處理耗時(shí)任務(wù)必須自己開啟一個(gè)線程。
4.IntentService可以處理耗時(shí)任務(wù)侧但，并且不需要關(guān)心是否開啟工作線程矢空，繼承它就可以了，實(shí)現(xiàn)onHandleIntent抽象方法處理耗時(shí)操作就行了禀横。
5.使用IntentService不需要關(guān)心關(guān)閉Service屁药。在任務(wù)完成后會(huì)自動(dòng)stopSelf掉。
6.由源碼看出柏锄，IntentService不適合用bindService啟動(dòng)酿箭，因?yàn)閛nBind返回null微服，同時(shí)用bindService IntentService也不會(huì)回調(diào)onHandleIntent方法准验，也不會(huì)在service任務(wù)完成后停止。如果使用bindService啟動(dòng)IntentService惜颇，那僅僅是一個(gè)普通的Service抬闷。
3.如何使用
3.1繼承IntentService實(shí)現(xiàn)onHandleIntent方法
/**
* Created by zw on 2019/7/7 11:31
*/
public class MyIntentService extends IntentService {
/**
* Creates an IntentService. Invoked by your subclass's constructor.
*
* @param name Used to name the worker thread, important only for debugging.
*/
public MyIntentService(String name) {
// 可以定義工作線程名稱
super(name);
}
@Override
protected void onHandleIntent(@Nullable Intent intent) {
// 處理耗時(shí)任務(wù)
}
}
3.2 AndriodManifest.xml中注冊(cè)這個(gè)Service
<service android:name=".MyIntentService"/>
3.3 啟動(dòng)服務(wù)
startService(new Intent(this, MyIntentService.class));
That's All
IntentService源碼onCreate方法里出現(xiàn)的Looper妇蛀，Message, Handler另外MessageQueue將在接下來分析它們。
