Android IntentService 分析和用法

IntentService的分析和用法，实用性介绍。

IntentService 简介

• IntentService继承自Service，可用startService启动，也需要在AndroidManifest.xml中注册
• IntentService在一个单独的worker线程中处理任务
• 任务完成后，会自动停止
• 可多次启动同一个IntentService，它们会自一个接一个地排队处理

IntentService 与 Service

耗时任务可以不用在Service中手动开启线程。
当操作完成时，我们不用手动停止IntentService，它会自动判定停止。

IntentService 自动停止

参考IntentService源码：

private volatile ServiceHandler mServiceHandler;

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); // 传入startID
    }
}

@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; // 这个是停止服务的依据
    msg.obj = intent;
    mServiceHandler.sendMessage(msg);
}

利用ServiceHandler来控制生命周期。onCreate方法中开启了一个HandlerThread来处理请求。
在onStart中获取到startId。在ServiceHandler中每次处理完一个命令都会调用stopSelf(int startId)方法来停止服务。
IntentService直到命令队列中的所有命令被执行完后才会停止服务。

用法示例

新建一个模拟计算的后台服务CalIntentService继承IntentService

/**
 * 模拟计算的后台服务
 * Created by Rust on 2017/6/9.
 */
public class CalIntentService extends IntentService {

    private static final String TAG = "rustApp";
    private int mStartId = 0;

    /**
     * 一定要一个无参构造器
     */
    public CalIntentService() {
        this("cal_intent_service_name");
    }

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

    @Override
    public void onStart(@Nullable Intent intent, int startId) {
        super.onStart(intent, startId);
        mStartId = startId;
        Log.d(TAG, "[CalIntentService] onStart, startId=" + mStartId); // 复写这个方法来看startId
    }

    @Override
    public void onDestroy() {
        super.onDestroy(); // 观察生命周期
        Log.d(TAG, "[CalIntentService] onDestroy. StartId=" + mStartId);
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) {
        if (null != intent) {
            String name = intent.getStringExtra("name");
            String msg = intent.getStringExtra("msg");
            Log.d(TAG, "[CalIntentService] 收到 name:" + name + ", msg:" + msg + ", at "
                    + Thread.currentThread().toString());
        }
        try {
            Thread.sleep(1000); // 模拟耗时操作
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        Log.d(TAG, "[CalIntentService] 计算结束.  mStartId=" + mStartId);
    }
}

AndroidManifest中注册这个服务。目前只允许本App使用

<service
    android:name="com.rustfisher.service.CalIntentService"
    android:exported="false" />

Activity中启动这个服务

btn2.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Intent calIntent = new Intent(getApplicationContext(), CalIntentService.class);
        calIntent.putExtra("name", "Rust");
        calIntent.putExtra("msg", "Click event: " + mClickCount++);
        startService(calIntent);
    }
});

在手机上运行，快速点击几次按钮，启动IntentService，logcat输出

[CalIntentService] onStart, startId=1
[CalIntentService] 收到 name:Rust, msg:Click event: 0, at Thread[IntentService[cal_intent_service_name],5,main]
[CalIntentService] onStart, startId=2
[CalIntentService] onStart, startId=3
[CalIntentService] onStart, startId=4
[CalIntentService] 计算结束.  最新StartId=4
[CalIntentService] 收到 name:Rust, msg:Click event: 1, at Thread[IntentService[cal_intent_service_name],5,main]
[CalIntentService] 计算结束.  最新StartId=4
[CalIntentService] 收到 name:Rust, msg:Click event: 2, at Thread[IntentService[cal_intent_service_name],5,main]
[CalIntentService] 计算结束.  最新StartId=4
[CalIntentService] 收到 name:Rust, msg:Click event: 3, at Thread[IntentService[cal_intent_service_name],5,main]
[CalIntentService] 计算结束.  最新StartId=4
[CalIntentService] onDestroy. StartId=4

可以看出，先执行onStart，然后排队执行onHandleIntent。任务全部结束后自行停止。