1. IntentService概述
- 它本质是一种特殊的Service,继承自Service并且本身就是一个抽象类
- 它可以用于在后台执行耗时的异步任务,当任务完成后会自动停止
- 它拥有较高的优先级,不易被系统杀死(继承自Service的缘故),因此比较适合执行一些高优先级的异步任务
- 它内部通过HandlerThread和Handler实现异步操作
- 创建IntentService时,只需实现onHandleIntent和构造方法,onHandleIntent为异步方法,可以执行耗时操作
2. 使用方法
新建一个类,继承自IntentService
public class MyIntentServic extends IntentService{
/**
需要实现一个无参的构造函数
*/
private static final String TAG = "MyIntentServic";
public MyIntentServic() {
super(TAG);
}
/**
实现onHandleIntent()方法。
*/
@Override
protected void onHandleIntent(Intent intent) {
String tag= intent.getStringExtra("tag");
Log.e(TAG, "ag-------->"+tag);
Log.e(TAG, "Thread.id----->"+Thread.currentThread());
try {
Thread.sleep(5*1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
/**
并且还在其他生命周期方法中打印了log日志。
*/
@Override
public void onCreate() {
super.onCreate();
Log.e(TAG, "-------->onCreate:");
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.e(TAG, "-------->onStartCommand:");
return super.onStartCommand(intent, flags, startId);
}
@Override
public void onDestroy() {
super.onDestroy();
Log.e(TAG, "-------->onDestroy:");
}
}
如何调用启动服务
void startService() {
Intent intent = new Intent(this,MyIntentServic.class);
tag++;
intent.putExtra("tag",tag+"");
startService(intent);
}
点击五次,查看打印log
打印log截图注:和service一样,开启五次onCreate只执行一次,可见service实例只有一个,onStartCommand执行了5次,onHandleIntent也执行了5次
2. 源码分析
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(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);
}
在onCreate()方法中,创建了一个线程HandlerThread对象,接着启动了该线程,然后将该线程的Looper对象赋值给内部类ServiceHandler。
ServiceHandler顾名思义,就是一个Handler,在它的handleMessage()方法中,调用了onHandleIntent((Intent)msg.obj)和stopSelf(msg.arg1)方法,而onHandleIntent((Intent)msg.obj)方法是一个抽象方法,需要用户自己实现;stopSelf(msg.arg1)方法,这不是停止Service的方法嘛!
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