IntentService 使用与原理

IntentService

简介

• 在Service里面不能直接进行耗时操作，一般都需要去开启子线程，如果自己去管理Service的生命周期以及子线程难免会不完善，Android提供了一个类，IntentService。
• IntentService是一个基于Service的一个类，用来处理异步的请求。你可以通过startService(Intent)来提交请求，该Service会在需要的时候创建，当完成所有的任务以后自己关闭，而不需要我们去手动控制

使用

需要继承IntentService，然后复写onHandleIntent方法

public class UploadImgService extends IntentService {

    private static final String ACTION_UPLOAD_IMG = "com.jsj.handlerthreaddemo.action.UPLOAD_IMAGE";
    public static final String EXTRA_IMG_PATH = "com.jsj.handlerthreaddemo.extra.IMG_PATH";


    /**
     * Creates an IntentService.  Invoked by your subclass's constructor.
     *
     * @param name Used to name the worker thread, important only for debugging.
     *             给线程设置名字
     */
    public UploadImgService(String name) {
        super(name);
    }

    public UploadImgService() {
        super("UploadImgService");
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) {
        if (intent != null) {
            final String action = intent.getAction();
            if (ACTION_UPLOAD_IMG.equals(action)) {
                final String path = intent.getStringExtra(EXTRA_IMG_PATH);//获取要处理的数据
                //TODO 处理数据，然后通过广播将数据发送出去
                Intent intent = new Intent(IntentServiceActivity.UPLOAD_RESULT);
                intent.putExtra(EXTRA_IMG_PATH, path);
                sendBroadcast(intent);//将处理完的数据通过广播的形式发送出去
            }
        }
    }

开启服务

//开启服务，并将需要处理的数据传递过去
Intent intent = new Intent(context, UploadImgService.class);
        intent.setAction(ACTION_UPLOAD_IMG);
        intent.putExtra(EXTRA_IMG_PATH, path);
        context.startService(intent);

通过广播接受者来接收发送过来的数据

private BroadcastReceiver uploadImgReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction() == UPLOAD_RESULT) {
                String path = intent.getStringExtra(UploadImgService.EXTRA_IMG_PATH);
                tv.setText(path + " upload success ~~~ ");
            }
        }
    };

源码

不多就都贴了出来，容易看

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);

分析

1.onCreate里面初始化了一个HandlerThread

@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);
    }

2.每次调用onStartCommand的时候，通过mServiceHandler发送一条带startId和Intent的消息，然后在该mServiceHandler的handleMessage中去回调onHandleIntent(intent);

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

当回调onHandleIntent(intent)后调用了方法stopSelf(msg.arg1);

 @Override
        public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }

跟下stopSelf方法，传入了一个int类型，当前发送的标识是最近发出的那一个

当所有的工作执行完后:就会执行onDestroy方法，然后调用方法 mServiceLooper.quit()使looper停下来.

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

总结：

• IntentService是继承于Service并处理异步请求的一个类

• 当完成所有的任务以后自己关闭，而不需要我们去手动控制

• 可以启动多次，每启动一次，就会新建一个work thread，但IntentService的实例始终只有一个，onCreate方法只执行了一次，而onStartCommand和onStart方法执行多次

• 在IntentService内拥有一个HandlerThread,获得工作线程的 Looper，并维护自己的工作队列

• 可以启动IntentService多次，而每一个耗时操作会以工作队列的方式在IntentService的onHandleIntent回调方法中执行，并且，每次只会执行一个工作线程，执行完第一个再执行第二个，按顺序执行