停止 AsyncTask 会导致服务结束

Question

我有一个运行两个异步任务的服务。一个用于接收组播数据包，另一个用于接收 udp 数据包。我已经注册了一个 wifi 状态监听器，并希望在与接入点的连接丢失时停止监听数据包。但是当我尝试关闭任何一个套接字并尝试结束 while 循环时，服务本身就会关闭。我希望该服务在我的活动退出之前一直运行。 以下是我的代码的相关部分。括号可能放错了...

public class ReceiveService extends Service {

private Receive r;
private ReceiveMulticast rm;
private boolean running = true;

private boolean receive = false, receivemulti = false;


@Override
public IBinder onBind(Intent arg0) {
    // return binder;
    return null;
}

@Override
public void onCreate() {

    try {

        r = new Receive();
        rm = new ReceiveMulticast();


        if (wifi.checkwifi(this)) {//check if connected to access point
            wifiInit();
            receive();
            receivemulti();
        }

    } catch (Exception e) {
        Log.d("test", "exception in oncreate");
        //e.printStackTrace();
    }

}

public void wifiInit() {
    wm = wifi.getWifiManager(this);
    myip = wifi.getmyip(wm);
    wifi.acquirelock(wm);
}

public void receive() {
    r.execute();
    receive = true;

}

public void receivemulti() {
    rm.execute();
    receivemulti = true;

}

private BroadcastReceiver WifiStateChangedReceiver = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {

        //monitor changes in wifi state
    }
};

@Override
public void onDestroy() {
    try {
        if (!r.ds1.isClosed())
            r.ds1.close();
        if (!rm.s.isClosed()) {
            rm.s.leaveGroup(rm.group);
            rm.s.close();
        }

        super.onDestroy();
    } catch (Exception e) {
        Log.d("test", "Exception in destroy");
    }
}

private class Receive extends AsyncTask<Void, String, Void> {

    private DatagramSocket ds1;
    private DatagramPacket p;

    protected void onPreExecute() {

    }

    protected Void doInBackground(Void... params) {

        try {
            ds1 = new DatagramSocket(7777);
        } catch (SocketException e) {
            Log.d("test", "Exception in new datagram");
            //e.printStackTrace();
        }
        int buffer_size = 1024;
        byte buffer1[] = new byte[buffer_size];
        p = new DatagramPacket(buffer1, buffer1.length);

        while (running) {
            try {
                ds1.receive(p);
                String sip = p.getAddress().getHostAddress();
                String rec = new String(p.getData(), 0, p.getLength());

                //publishProgress(sip + "+" + rec);
            } catch (Exception e) {

                running = false;
            }
        }
        return null;

    }

    protected void onProgressUpdate(String... progress) {
        //do stuff

    }

    protected void onPostExecute(Void result) {
        stopSelf();
    }

}

private class ReceiveMulticast extends AsyncTask<Void, String, Void> {

    private String ip = "224.0.0.10";
    private int port = 6789;
    private MulticastSocket s;
    private DatagramPacket mp;
    private InetAddress group;

    protected void onPreExecute() {

    }

    protected Void doInBackground(Void... params) {

        try {
            group = InetAddress.getByName(ip);
            s = new MulticastSocket(port);
            s.joinGroup(group);
        } catch (UnknownHostException e1) {
            Log.d("test", "exception unknown host rm");

            //e1.printStackTrace();
        } catch (IOException e) {
            Log.d("test", "exception io rm");

            //e.printStackTrace();
        }

        byte[] buffer2 = new byte[1024];
        mp = new DatagramPacket(buffer2, buffer2.length);

        while (running) {

            try {
                s.receive(mp);
                String sip = mp.getAddress().getHostAddress();
                String rec = new String(mp.getData(), 0, mp.getLength());

                //publishProgress(sip + "+" + rec);
            } catch (Exception e) {

                running = false;

            }
        }
        return null;
    }

    protected void onProgressUpdate(String... progress) {

        //do stuff


        }

    }

    protected void onPostExecute(Void result) {
        stopSelf();
    }
}

}

Answer 1

正常停止还是异常停止？

您正在 AsyncTask 之一的 postExecute() 中调用 stopSelf()。如果您遇到异常，您的 while(true) ... 循环将退出，然后调用 postExecute()，它调用 stopSelf()。这可能是原因，但由于您没有记录异常，因此无法知道。

Answer 2

AsyncTask 只能在 UI 线程上运行。