Host is null in NsdServiceInfo of NsdManager.DiscoveryListener.onServiceFound

问题:

I'm trying to get the mHost of the NsdServiceInfo passed as parameter to NsdManager.DiscoveryListener.onServiceFound() but it's null. I have two android devices where device 1 is the server and device 2 is the client.

This is how I register the server in the device 1

public void registerService(int port, InetAddress myIp) {     NsdServiceInfo serviceInfo  = new NsdServiceInfo();     serviceInfo.setPort(port);     serviceInfo.setServiceName(this.serviceName);     serviceInfo.setServiceType(SERVICE_TYPE);     serviceInfo.setHost(myIp);      this.nsdManager.registerService(             serviceInfo, NsdManager.PROTOCOL_DNS_SD, registrationListener); } 

And this is how I initialize the DiscoveryListener

public void initializeDiscoveryListener() {     discoveryListener = new NsdManager.DiscoveryListener() {          @Override         public void onServiceFound(NsdServiceInfo service) {             Log.d(TAG, "Service discovery success" + service);             if (!service.getServiceType().equals(SERVICE_TYPE)) {                 Log.d(TAG, "Unknown Service Type: " + service.getServiceType());             } else if (service.getHost() == myIp) {                 Log.d(TAG, "Same machine: " + service.getHost());             } else if (service.getServiceName().contains(serviceName)){                 nsdManager.resolveService(service, resolveListener);             }         }    ...    } } 

But service.getHost() returns null.
Any suggestion?

回答1:

I just ran across this same issue and managed to solve it with a little help from Google's page on network discovery.

http://developer.android.com/training/connect-devices-wirelessly/nsd.html

The problem is that the connection information isn't known when the service is discovered. You have to resolve it first before getHost() will work.

You already have the line:

    nsdManager.resolveService(service, resolveListener); 

The resolveListener variable contains callbacks for success and failure. You want to use getHost() when the connection information has been successfully determined. Here's the resolve listener from Google:

    public void initializeResolveListener() {         resolveListener = new NsdManager.ResolveListener() {          @Override         public void onResolveFailed(NsdServiceInfo serviceInfo, int errorCode) {             // Called when the resolve fails.  Use the error code to debug.             Log.e(TAG, "Resolve failed" + errorCode);         }          @Override         public void onServiceResolved(NsdServiceInfo serviceInfo) {             Log.e(TAG, "Resolve Succeeded. " + serviceInfo);              if (serviceInfo.getServiceName().equals(mServiceName)) {                 Log.d(TAG, "Same IP.");                 return;             }             service = serviceInfo;             int port = service.getPort();             InetAddress host = service.getHost(); // getHost() will work now         }     }; } 

文章来源: Host is null in NsdServiceInfo of NsdManager.DiscoveryListener.onServiceFound