如何使用IntentService

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参考 https://developer.android.google.cn/reference/android/app/IntentService.html

IntentService定义

IntentService继承与Service，用来处理异步请求。客户端可以通过startService(Intent)方法传递请求给IntentService。IntentService在onCreate()方法中通过HandlerThread单独开启一个线程来依次处理所有Intent请求对象所对应的任务，这样以免事务处理阻塞主线程(ANR)。执行完所一个Intent请求对象所对应的工作之后，如果没有新的Intent请求达到，则**自动停止**Service；否则执行下一个Intent请求所对应的任务。
IntentService在处理事务时，还是采用的Handler方式，创建一个名叫ServiceHandler的内部Handler，并把它直接绑定到HandlerThread所对应的子线程。 ServiceHandler把处理一个intent所对应的事务都封装到叫做onHandleIntent的抽象方法；因此我们直接实现抽象方法onHandleIntent，再在里面根据Intent的不同进行不同的事务处理就可以了。另外，IntentService默认实现了onbind()方法，返回值为null。

源码

public abstract class IntentService extends Service {    private volatile Looper mServiceLooper;    private volatile ServiceHandler mServiceHandler;    private String mName;    private boolean mRedelivery;    // 内部Handler处理    private final class ServiceHandler extends Handler {        public ServiceHandler(Looper looper) {            super(looper);        }        @Override        public void handleMessage(Message msg) {            onHandleIntent((Intent)msg.obj);            // 关闭当前Service            stopSelf(msg.arg1);        }    }    public IntentService(String name) {        super();        mName = name;e;         }    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) {        // 发送消息(Intent)        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;    }    // 需要覆盖该方法进行一步处理    @WorkerThread    protected abstract void onHandleIntent(@Nullable Intent intent);}

实现方式

定义一个TestIntentService继承IntentService

public class TestIntentService extends IntentService {    // 注意构造函数参数为空，这个字符串就是WorkThread的名字    public TestIntentService() {        super("TestIntentService");    }    @Override    public void onCreate() {        Log.d("TIS","onCreate()");        super.onCreate();    }    @Override    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {        Log.d("TIS","onStartCommand()");        return super.onStartCommand(intent, flags, startId);    }    @Override    public void onDestroy() {        super.onDestroy();        Log.d("TIS","onDestroy()");    }    @Override    protected void onHandleIntent(@Nullable Intent intent) {        if (intent != null) {            int taskId = intent.getIntExtra("taskId", -1);            // 依次处理Intent请求            switch (taskId) {                case 0:                    Log.d("TIS","handle task0");                    break;                case 1:                    Log.d("TIS","handle task1");                    break;                case 2:                    Log.d("TIS","handle task2");                    break;            }        }    }}

Manifest.xml中注册

<application    ........>    <activity .../>    <service android:name=".service.TestIntentService" /></application>

启动Service

//同一服务只会开启一个WorkThread，在onHandleIntent函数里依次处理Intent请求。Intent i0 = new Intent(this, TestIntentService.class);Bundle b0 = new Bundle();b0.putInt("taskId",0);i0.putExtras(b0);startService(i0);Intent i1 = new Intent(this, TestIntentService.class);Bundle b1 = new Bundle();b1.putInt("taskId",1);i1.putExtras(b1);startService(i1);Intent i2 = new Intent(this, TestIntentService.class);Bundle b2 = new Bundle();b2.putInt("taskId",2);i2.putExtras(b2);startService(i2);startService(i1);startService(i0);

运行结果及生命周期

D/TIS: onCreate()D/TIS: onStartCommand()D/TIS: handle task0D/TIS: onStartCommand()D/TIS: onStartCommand()D/TIS: onStartCommand()D/TIS: handle task1D/TIS: onStartCommand()D/TIS: handle task2D/TIS: handle task1D/TIS: handle task0D/TIS: onDestroy()

Android Studio自动创建IntentService如下:

代码没做，模板代码是提供静态方法，方便调用，推荐使用这种方式

public class HelloIntentService extends IntentService {    // TODO: Rename actions, choose action names that describe tasks that this    // IntentService can perform, e.g. ACTION_FETCH_NEW_ITEMS    private static final String ACTION_FOO = "com.cyxoder.interstudy.service.action.FOO";    private static final String ACTION_BAZ = "com.cyxoder.interstudy.service.action.BAZ";    // TODO: Rename parameters    private static final String EXTRA_PARAM1 = "com.cyxoder.interstudy.service.extra.PARAM1";    private static final String EXTRA_PARAM2 = "com.cyxoder.interstudy.service.extra.PARAM2";    public HelloIntentService() {        super("HelloIntentService");    }    /**     * Starts this service to perform action Foo with the given parameters. If     * the service is already performing a task this action will be queued.     *     * @see IntentService     */    // TODO: Customize helper method    public static void startActionFoo(Context context, String param1, String param2) {        Intent intent = new Intent(context, HelloIntentService.class);        intent.setAction(ACTION_FOO);        intent.putExtra(EXTRA_PARAM1, param1);        intent.putExtra(EXTRA_PARAM2, param2);        context.startService(intent);    }    /**     * Starts this service to perform action Baz with the given parameters. If     * the service is already performing a task this action will be queued.     *     * @see IntentService     */    // TODO: Customize helper method    public static void startActionBaz(Context context, String param1, String param2) {        Intent intent = new Intent(context, HelloIntentService.class);        intent.setAction(ACTION_BAZ);        intent.putExtra(EXTRA_PARAM1, param1);        intent.putExtra(EXTRA_PARAM2, param2);        context.startService(intent);    }    @Override    protected void onHandleIntent(Intent intent) {        if (intent != null) {            final String action = intent.getAction();            if (ACTION_FOO.equals(action)) {                final String param1 = intent.getStringExtra(EXTRA_PARAM1);                final String param2 = intent.getStringExtra(EXTRA_PARAM2);                handleActionFoo(param1, param2);            } else if (ACTION_BAZ.equals(action)) {                final String param1 = intent.getStringExtra(EXTRA_PARAM1);                final String param2 = intent.getStringExtra(EXTRA_PARAM2);                handleActionBaz(param1, param2);            }        }    }    /**     * Handle action Foo in the provided background thread with the provided     * parameters.     */    private void handleActionFoo(String param1, String param2) {        // TODO: Handle action Foo        throw new UnsupportedOperationException("Not yet implemented");    }    /**     * Handle action Baz in the provided background thread with the provided     * parameters.     */    private void handleActionBaz(String param1, String param2) {        // TODO: Handle action Baz        throw new UnsupportedOperationException("Not yet implemented");}

原理
IntentService在onCreate()函数中通过HandlerThread单独开启一个线程来依次处理所有Intent请求对象所对应的任务。通过onStartCommand()传递给服务intent被依次插入到工作队列中。工作队列又把intent逐个发送给onHandleIntent()。

注意：所有请求都是在一个单独的工作线程上处理的——它们可能会在必要的时候（并不会阻塞应用程序的主循环），但每次只处理一个请求。

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