IntentService解析及使用规范

IntentService解析及使用规范

一、概述

IntentService继承于Service用来在后台处理异步请求。客户端通过
Context#startService(Intent)发送请求，IntentService按顺序在后台工作线程里处理每一个Intent，并且当处理完所有Intent就会停止。

#1-1 使用示例

#MainActivity.java
   String param = "this is a test case.";
    TestIntentService.startActionTest(this,param);

#TestIntentService.java
public class TestIntentService extends IntentService {

    private static final String TAG = "TestIntentService";

    private static final String ACTION_TEST = "action.TEST";
    private static final String EXTRA_PARAM1 = "extra.PARAM1";

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

    public static void startActionTest(Context context, String param1) {
        Intent intent = new Intent(context, TestIntentService.class);
        intent.setAction(ACTION_TEST);
        intent.putExtra(EXTRA_PARAM1, param1);
        context.startService(intent);
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        if (intent != null) {
            final String action = intent.getAction();
            if (ACTION_TEST.equals(action)) {
                final String param1 = intent.getStringExtra(EXTRA_PARAM1);
                handleActionTest(param1);
            }
        }
    }

    private void handleActionTest(String param1) {
        Log.d(TAG,"handleActionTest(String param1) param1:" + param1);

    }
}

二、IntentService

#2-1 源代码

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);
        }
    }

    public IntentService(String name) {
        super();
        mName = name;
    }

    public void setIntentRedelivery(boolean enabled) {
        mRedelivery = enabled;
    }

    @Override
    public void onCreate() {
        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);
    }

    @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();
    }

    @Override
    @Nullable
    public IBinder onBind(Intent intent) {
        return null;
    }

    @WorkerThread
    protected abstract void onHandleIntent(@Nullable Intent intent);
}

#2-2 创建Service

在Service被创建的时候，使用HandlerThread（继承于 Thread）创建一个多线程并运行起来，使用HandlerThread线程的Looper来创建一个Handler，使得此Handler处理的所有任务都运行在非主线程里。

   public void onCreate() {
        super.onCreate();
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

#2-3 处理任务

onStart在高版本SDK被onStartCommand替代，为了兼容低版本在onStartCommand调用onStart方法。任务最终通过运行在非主线程的onHandleIntent执行。

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

    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICK;
    }

    @WorkerThread
    protected abstract void onHandleIntent(@Nullable Intent intent);

#2-4 销毁Service

任务执行完毕后会调用stopSelf，在没有任何任务正在执行或即将执行的情况下Service会停止运行。

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

#2-5 注意事项

Service停止运行时要注意使用mServiceLooper.quit()退出Looper。如果不提供绑定服务默认返回null。

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

    @Override
    @Nullable
    public IBinder onBind(Intent intent) {
        return null;
    }

三、知识点总结

#3-1 HandlerThread

使用HandlerThread和Handler创建一个子线程独立运行，Handler#sendMessage(msg)将任务放在该子线程即将执行的任务队列里。

        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);

#3-2 Handler

使用Handler发送消息时通过obtainMessage()来获取消息，它有个消息池可以循环利用避免创建过多的Message消耗不必要的内存

        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);