在Android中使用网络服务发现的内部错误

概述在使用示例和 tutorial on the developer page首次实施NSDManager期间,应用程序成功启动了发现并找到了设备. 然而现在它似乎被打破了…… 程序启动后,在初始化后,代码进入以下方法并成功运行： public void discoverServices() { Log.d(TAG, "Initializing discovery on NSD"); 在使用示例和 tutorial on the developer page首次实施NSDManager期间,应用程序成功启动了发现并找到了设备. @H_403_2@然而现在它似乎被打破了……

@H_403_2@程序启动后,在初始化后,代码进入以下方法并成功运行：

public voID discoverServices() {    Log.d(TAG,"Initializing discovery on NSD");    mNsdManager.discoverServices(            SERVICE_TYPE,NsdManager.PROTOCol_DNS_SD,mdiscoveryListener);}

@H_403_2@收到日志消息.经过一段时间(约5分钟),这是从程序输出：

05-21 11:08:32.518: E/NsdCamera(12236): discovery Failed: Error code:005-21 11:08:32.518: W/dalvikvm(12236): threadID=12: thread exiting with uncaught exception (group=0x40c9c930)05-21 11:08:32.518: E/AndroIDRuntime(12236): FATAL EXCEPTION: NsdManager05-21 11:08:32.518: E/AndroIDRuntime(12236): java.lang.NullPointerException05-21 11:08:32.518: E/AndroIDRuntime(12236):    at androID.net.nsd.NsdManager$ServiceHandler.handleMessage(NsdManager.java:338)05-21 11:08:32.518: E/AndroIDRuntime(12236):    at androID.os.Handler.dispatchMessage(Handler.java:99)05-21 11:08:32.518: E/AndroIDRuntime(12236):    at androID.os.Looper.loop(Looper.java:137)05-21 11:08:32.518: E/AndroIDRuntime(12236):    at androID.os.HandlerThread.run(HandlerThread.java:60)

@H_403_2@还来自服务：

05-21 11:50:49.108: E/NativeDaemonConnector.ResponseQueue(8858): Timeout waiting for response05-21 11:50:49.108: E/mDnsConnector(8858): timed-out waiting for response to 10 mdnssd discover 6 _http._tcp.05-21 11:50:49.108: E/NsdService(8858): Failed to discoverServices com.androID.server.NativeDaemonConnector$NativeDaemonFailureException: command '10 mdnssd discover 6 _http._tcp.' Failed with 'null'

@H_403_2@错误代码“0”在NSDManager class中描述为内部错误.
我做的主要更新是访问名为NsdCamera的helper类中的上下文.
这里有一些可能是邪恶的代码片段：

@H_403_2@助手级构造函数：

public NsdCamera(CameraChooseActivity context) {    mContext = context;    updateUI =  new UpdateUI();    mNsdManager = (NsdManager) context.getSystemService(Context.NSD_SERVICE);    mServicename = new Vector<NsdServiceInfo>();

@H_403_2@Helper级NSD初始化：

public voID initialiZensd() {    initializediscoveryListener();}public voID initializediscoveryListener() {    mdiscoveryListener = new NsdManager.discoveryListener() {        @OverrIDe        public voID ondiscoveryStarted(String regType) {            Log.d(TAG,"Service discovery started");        }        /**         * A name check to see if the DNS discovery was correct. Checks if it contains          * AXIS and has the desired MAC address-space         * @param hostname,the inputted hostname from the discovery cycle         * @return true if it's an Axis camera.          */        public boolean nameCheck(String hostname){            return (hostname.contains("AXIS") && hostname.contains("00408C"));        }        @OverrIDe        public voID onServiceFound(NsdServiceInfo service) {            Log.d(TAG,"Service discovery success: " + service.getServicename());            if (!service.getServiceType().equals(SERVICE_TYPE)) {                Log.d(TAG,"UnkNown Service Type: " + service.getServiceType());            } else if (nameCheck(service.getServicename())){                mServicename.add(service);//                  updateUI.execute(new BundleUI(mContext,service,null));            }        }        @OverrIDe        public voID onServiceLost(NsdServiceInfo service) {            Log.e(TAG,"service lost" + service);            if(mServicename.remove(service)){                //Todo                Log.e(TAG,"remove the vIEw,service is lost");            }        }        @OverrIDe        public voID ondiscoveryStopped(String serviceType) {            Log.i(TAG,"discovery stopped: " + serviceType);            //Necessary??            mServicename.clear();        }        @OverrIDe        public voID onStartdiscoveryFailed(String serviceType,int errorCode) {            Log.e(TAG,"discovery Failed: Error code:" + errorCode);            mNsdManager.stopServicediscovery(this);        }        @OverrIDe        public voID onStopdiscoveryFailed(String serviceType,"discovery Failed: Error code:" + errorCode);            mNsdManager.stopServicediscovery(this);        }    };}

@H_403_2@CameraChooseActivity – > onCreate正在调用helper-class

protected voID onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentVIEw(R.layout.activity_camerachoose);    //Setup the animation for the text in the relativelayout    mDescription = (TextSwitcher) findVIEwByID(R.ID.camera_add);    mDescription.setFactory(this);    mDescription.setInAnimation(AnimationUtils.loadAnimation(this,androID.R.anim.fade_in));    mDescription.setoutAnimation(AnimationUtils.loadAnimation(this,androID.R.anim.fade_out));    mDescription.setText(getText(R.string.camera_add));    //Building alert dialog    mBuilder = new AlertDialog.Builder(this,AlertDialog.theme_HolO_DARK);    mBuilder.setMessage(R.string.dialog_about).setTitle(R.string.action_about);    mBuilder.setIcon(androID.R.drawable.ic_dialog_info);    mLayout = (relativeLayout) findVIEwByID(R.ID.layout_camerachoose);    //Initialize the NSD    mNSDHelper = new NsdCamera(this);    mNSDHelper.initialiZensd();

解决方法 根据我的经验,我认为这是一个听众终身问题. @H_403_2@因为您为系统NSD服务提供了两个侦听器,一个用于startServicediscovery(),另一个用于stopServicediscovery().当系统访问这些侦听器时,您需要确保这些侦听器仍处于活动状态.

@H_403_2@一个事实是,在调用startServicediscovery()2分钟后调用onStartdiscoveryFailed(),与侦听器的生命周期相比,它应该是一个很长的时间.

@H_403_2@因此,如果侦听器是本地对象并在调用startServicediscovery()之后释放,则可能导致NSD服务崩溃.

@H_403_2@public voID stopServicediscovery (NsdManager.discoveryListener
Listener)

@H_403_2@Stop service discovery initiated with discoverServices(). An active
service discovery is notifIEd to the application with
ondiscoveryStarted(String) and it stays active until the application
invokes a stop service discovery. A successful stop is notifIEd to
with a call to ondiscoveryStopped(String).

@H_403_2@Upon failure to stop service discovery,application is notifIEd
through onStopdiscoveryFailed(String,int).

@H_403_2@Parameters Listener This should be the Listener object that was passed
to discoverServices(String,int,NsdManager.discoveryListener). It
IDentifIEs the discovery that should be stopped and notifIEs of a
successful stop.

@H_403_2@并在下面的代码段确保不要调用任何NsdManager API.

@OverrIDepublic voID onStartdiscoveryFailed(String serviceType,int errorCode) {     Log.i(TAG,"onStartdiscoveryFailed : Error code:" + errorCode);}@OverrIDepublic voID onStopdiscoveryFailed(String serviceType,int errorCode) {    Log.i(TAG,"onStopdiscoveryFailed : Error code:" + errorCode);}

@H_403_2@祝好运.

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