Is Android WifiP2pManager.discoverServices able to discover NsdServiceInfo (by NsdManager.registerService)?

See also questions close to this topic

• Questions about the responsbilities of each component in Android Architecture Components

  I've been using MVP for a long time now and I'm starting to transfer to a hybrid state between MVP and MVVM

  In detail my apps will go like this:

  • Each Activity has a 0 to x Fragments that represent its views
  • Each Fragment will request the Activity's ViewModel so that they can retrieve data using LiveData
  • The Activity will have a seperate ViewModel which will act as the presenter. On creation that ViewModel will be injected with the Activity's ViewModel with the LiveData so that it can update the UI as needed
  • The presenter will get the messages sent to the data ViewModel and send the results back to it

  My questions:

  1. Could holding a reference to the data ViewModel in the presenter ViewModel cause a memory leak or adverse effects such as memory leaks?
  2. Where should business logic be? in the presenter or in the model part?

  For example, let's say I have a list of items and the user long presses one to edit them, what part of this architecture should be responsible for checking if the user has permission to do this and either let them edit the item or show an error message?

  3. Is there a way for the Fragments to only get part of the Activity's ViewModel?

  For example , assuming the activity has 3 Fragments under it, and one ViewModel to cater to them

  Can I use something like:

  class MainViewModel : ViewModel() , IFragmentA, IFragmentB, IFragmentC
  

  and then when I try to get the ViewModel in the fragments I can write something like:

  lateinit var viewModel: IFragmentA
  
  override fun onAttach(context: Context?) {
      super.onAttach(context)
      vm = ViewModelProviders.of(context as AppCompatActivity).get(IFragmentA::class.java)
  }
  

  note:I know the above code does not work , what I am asking is if there is a way for something similar to this could work

  4. Is the correct way to send back messages to the activity SingleEvents?

  For example, if the user tries to delete an entry , and I wish for them to enter a password, would the flow be:

  • The Fragment sends the message to delete to its ViewModel
  • The ViewModel passes it on to the Presenter
  • The Presenter decides that it needs password verification before moving on
  • The presenter sets the value of a SingleEvent in ViewModel
  • The ViewModel notifies the event's subscribers (in this case the MainActivity) that they should show a dialog asking for a password

  Thank you for any help you can provide
• Google Fitness: Dealing with TransactionTooLargeException without feedback

  I'm building an application integrating with Google Fit via the local (not REST) Google Fit API. I'm using Flutter 1.2.1, Kotlin 1.3.21, com.google.android.gms:play-services-fitness:16.0.1 and running the app on Android 8.1.0 with Google Play Services 16.0.89.

  Some HistoryClient.readData() requests disappear without any feedback (no calls to onSuccessListener, onCancelledListener, onFailureListener, onCompleteListener callbacks), and at these times I can see in the logs:

     W/Fitness: Error delivering batch 0. Attempt #2
      android.os.TransactionTooLargeException: data parcel size 572360 bytes
          at android.os.BinderProxy.transactNative(Native Method)
          at android.os.BinderProxy.transact(Binder.java:777)
          at crb.c(:com.google.android.gms@16089017@16.0.89 (040306-239467275):1)
          at yek.a(Unknown Source:8)
          at yta.a(:com.google.android.gms@16089017@16.0.89 (040306-239467275):52)
          at yta.a(:com.google.android.gms@16089017@16.0.89 (040306-239467275):31)
          at ytc.run(:com.google.android.gms@16089017@16.0.89 (040306-239467275):44)
          at rrt.b(:com.google.android.gms@16089017@16.0.89 (040306-239467275):32)
          at rrt.run(:com.google.android.gms@16089017@16.0.89 (040306-239467275):21)
          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
          at rxx.run(Unknown Source:7)
          at java.lang.Thread.run(Thread.java:764)
  

  My understanding is that either the local Fitness service (part of Google Play Services) fails to send a notification about failure, or that the client library to Google Fit that I'm using fails to pass it along. Is this correct?

  How are others using this API to workaround this problem? What's a good timespan to ask for to be reasonably certain that it will complete successfully on all phones?

  Note: I tried posting this as a bug on https://issuetracker.google.com/issues/130402455, but I didn't get a response and I'm not even sure if it was the right place for that.
• Unresolved class '@string/appbar_scrolling_view_behavior' in fragment results into behaviour OnCreate not fired

  Please refer to my below fragment .XML

  <?xml version="1.0" encoding="utf-8"?>
  <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:id="@+id/consulting_frame"
      tools:context=".fragments.ConsultingFragment">
  
      <!-- TODO: Update blank fragment layout -->
      <android.support.design.widget.CoordinatorLayout
          android:id="@+id/main_content"
          android:layout_width="match_parent"
          android:layout_height="match_parent">
  
          <android.support.design.widget.AppBarLayout
              android:id="@+id/appbar"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
  
              <android.support.design.widget.TabLayout
                  android:id="@+id/consulting_tabs"
                  app:tabSelectedTextColor="@color/colorPrimaryDark"
                  app:tabIndicatorColor="@color/colorPrimary"
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content"
                  app:tabMode="scrollable"/>
          </android.support.design.widget.AppBarLayout>
  
          <android.support.v4.view.ViewPager
              android:id="@+id/viewpager"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              **app:layout_behavior="@string/appbar_scrolling_view_behavior"/>**
  
      </android.support.design.widget.CoordinatorLayout>
  

  in the above file line

  app:layout_behavior="@string/appbar_scrolling_view_behavior"/>
  

  displays error "Unresolved reference" in the editor, however it doesn't generate any compilation error.

  I have searched net and stackoverflow to find solution, it has mentioned that

  implementation 'com.android.support:design:28.0.0'
  implementation 'com.android.support:support-v4:28.0.0'
  

  must be included in the app gradle file. I have checked it, and both files are there in my app gradle file.

  I am not able to resolve the error. Please help with this error. Further to above error, I am also facing other erratic behaviour in my app, which is as explained below:

  When my above viewpager (Containing error) is initialized, I am instantiating four tabs and where four fragments are opened. My fragment file is as below:

  package com.mobiapp.hospmgmt.fragments;
  
  
  import android.os.Bundle;
  import android.support.annotation.Nullable;
  import android.support.design.widget.TabLayout;
  import android.support.v4.app.Fragment;
  import android.support.v4.app.FragmentManager;
  import android.support.v4.app.FragmentPagerAdapter;
  import android.support.v4.view.ViewPager;
  import android.view.LayoutInflater;
  import android.view.View;
  import android.view.ViewGroup;
  
  import com.mobiapp.hospmgmt.R;
  import com.mobiapp.hospmgmt.SessionHandler;
  import com.mobiapp.hospmgmt.User;
  import com.mobiapp.hospmgmt.helper.HospMgmtConstants;
  
  import java.util.ArrayList;
  import java.util.List;
  
  
  /**
   * A simple {@link Fragment} subclass.
   */
  public class ConsultingFragment extends Fragment {
  
      private SessionHandler session;
      User user;
  
      public ConsultingFragment() {
          // Required empty public constructor
      }
  
      @Override
      public void onCreate(@Nullable Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
  
          getActivity().setTitle(HospMgmtConstants.TAG_CONSULTING);
  
          session = new SessionHandler(getContext());
          user = session.getUserDetails();
  
      }
  
      @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
                               Bundle savedInstanceState) {
          // Inflate the layout for this fragment
  
          View view = inflater.inflate(R.layout.fragment_consulting, container, false);
          // Setting ViewPager for each Tabs
          ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewpager);
          setupViewPager(viewPager);
          // Set Tabs inside Toolbar
          TabLayout tabs = (TabLayout) view.findViewById(R.id.consulting_tabs);
          tabs.setupWithViewPager(viewPager);
  
  
          return view;
  
      }
  
      private void setupViewPager(ViewPager viewPager) {
  
          Adapter adapter = new Adapter(getChildFragmentManager());
          adapter.addFragment(new PatientConsultingFragment(), "Patient");
          adapter.addFragment(new DiagnosisConsultingFragment(), "Diagnosis");
          adapter.addFragment(new LabtestsConsultingFragment(), "Lab Tests");
          adapter.addFragment(new PrescribeConsultingFragment(), "Prescribe");
          viewPager.setAdapter(adapter);
  
      }
  
      static class Adapter extends FragmentPagerAdapter {
          private final List<Fragment> mFragmentList = new ArrayList<>();
          private final List<String> mFragmentTitleList = new ArrayList<>();
  
          public Adapter(FragmentManager manager) {
              super(manager);
          }
  
          @Override
          public Fragment getItem(int position) {
              return mFragmentList.get(position);
          }
  
          @Override
          public int getCount() {
              return mFragmentList.size();
          }
  
          public void addFragment(Fragment fragment, String title) {
              mFragmentList.add(fragment);
              mFragmentTitleList.add(title);
          }
  
          @Override
          public CharSequence getPageTitle(int position) {
              return mFragmentTitleList.get(position);
          }
      }
  }
  

  Now, issue is along with first fragment, second fragment is also getting instantiated, and onCreate method is fired for both. However, after that even if, I click on tab-2 (Diagnosis), onCreate is not fired. However, for other two fragments (TAB-3 (Lab Tests) and TAB-4 (Prescribe)) every time onCreate is getting fired whenever those tabs are clicked.

  I am failed to understand this erratic behaviour. Is this due to above Unresolved reference? I have tried to remove the line app:layout_behavior="@string/appbar_scrolling_view_behavior", but above erratic behaviour remains as it is.

  So, please help me in resolving above mentioned unresolved reference error and also above erratic behaviour of fragment initialization.
• Setup Android Wi-Fi P2P local service without ability to connect

  I would like to setup Android Wi-Fi P2P local service with some dns records, and i've already done it. My application needs only these records and there is no needs to make connection between peers. But I'm facing with a problem, the service is visible from other android users, and they could try to connect to my application's service. My app's user will see acceptance dialog: "Accept sharing request?" and it's quite annoying. Is there any way to make my service not accessible or drop connections before showing acceptance dialog or make password authentication like in wifi hotspot? Thanks.

  private WifiP2pManager manager;
  private WifiP2pManager.Channel channel;
  private WifiP2pDnsSdServiceInfo serviceInfo;
  private final int PERIOD = 5000;
  private String Tag = "WifiP2PService";
  String SERVICE_INSTANCE = "P2p_Service";
  private WifiP2pDnsSdServiceRequest serviceRequest;
  
  public WifiP2PService(Context ctx){
      manager = (WifiP2pManager) ctx.getSystemService(Context.WIFI_P2P_SERVICE);
      channel = manager.initialize(ctx, ctx.getMainLooper(), null);
      serviceRequest = WifiP2pDnsSdServiceRequest.newInstance();
      Map record = new HashMap();
      record.put("user_id", ""+(int)(Math.random() * 1000));
      serviceInfo = WifiP2pDnsSdServiceInfo.newInstance(SERVICE_INSTANCE, "_http._tcp", record);
      manager.setDnsSdResponseListeners(channel, null, new WifiP2pManager.DnsSdTxtRecordListener() {
          @Override
          public void onDnsSdTxtRecordAvailable(String fullDomainName, Map<String, String> txtRecordMap, WifiP2pDevice srcDevice) {
              Log.i(Tag, "Finded: "+txtRecordMap.get("user_id"));
          }
      });
  }
  
  public void startBroadcastingService(){
      manager.clearLocalServices(channel, new WifiP2pManager.ActionListener() {
          @Override
          public void onSuccess() {
              manager.addLocalService(channel, serviceInfo,
                      new WifiP2pManager.ActionListener() {
                          @Override
                          public void onSuccess() {
                              Log.i(Tag, "Started");
                              setWifiDirectName("WifiP2p Android");
                          }
  
                          @Override
                          public void onFailure(int error) {
                              Log.i(Tag, "Failed to start");
                          }
                      });
          }
  
          @Override
          public void onFailure(int error) {
              Log.i(Tag, "Failed to clean");
          }
      });
  }
  
  public void startSearching() {
      manager.removeServiceRequest(
              channel,
              serviceRequest,
              new WifiP2pManager.ActionListener() {
                  @Override
                  public void onSuccess() {
                      manager.addServiceRequest(channel, serviceRequest, new WifiP2pManager.ActionListener() {
                                  @Override
                                  public void onSuccess() {
                                      manager.discoverServices(channel, new WifiP2pManager.ActionListener() {
                                          @Override
                                          public void onSuccess() {
  
                                          }
                                          @Override
                                          public void onFailure(final int error) {
                                          }
                                      });
                                  }
                                  @Override
                                  public void onFailure(final int reason) {
                                  }
                              }
                      );
                  }
                  @Override
                  public void onFailure(final int reason) {
                  }
              }
      );
  }
  
  public void setWifiDirectName(final String deviceName) {
      try {
          final Class[] paramTypes = new Class[3];
          paramTypes[0] = WifiP2pManager.Channel.class;
          paramTypes[1] = String.class;
          paramTypes[2] = WifiP2pManager.ActionListener.class;
          final Method setDeviceName = manager.getClass().getMethod(
                  "setDeviceName", paramTypes);
          setDeviceName.setAccessible(true);
  
          final Object[] arglist = new Object[3];
          arglist[0] = channel;
          arglist[1] = deviceName;
          setDeviceName.invoke(manager, arglist);
      } catch (final Exception e) {
          e.printStackTrace();
      }
  }
  
  public void stopLocalService() {
      Log.i(Tag, "Stopped");
      manager.clearLocalServices(channel, null);
      manager.removeServiceRequest(channel, serviceRequest, null);
  }
  
• App crash while sending data over a socket using WifiP2p connection

  App crashes while sending data over a socket using wifi p2p connection

  I am testing a simple chat application between HTC_Desire_10 pro (running Android 6.0) and OPPO A83 (running Android 7.1.1). I have the same app running on the two devices. The app first turns wifi on, then starts discovering peers on a users click event. The user can choose the device they want to connect to from a dynamically generated peer list. The two devices are able to connect successfully. I am able to send a text message from the HTC to OPPO phone but when I try to send a message from the OPPO phone, the app crashes.

  This is the code that assigns which device will be the host or client

  WifiP2pManager.ConnectionInfoListener connectionInfoListener = new WifiP2pManager.ConnectionInfoListener() {
      @Override
      public void onConnectionInfoAvailable(WifiP2pInfo wifiP2pInfo) {
          final InetAddress groupOwnerAddress = wifiP2pInfo.groupOwnerAddress;
          if(wifiP2pInfo.groupFormed&&wifiP2pInfo.isGroupOwner) {
              ConnectionStatus.setText("Host");
              serverClass = new ServerClass();
              serverClass.start();
          } else if(wifiP2pInfo.groupFormed) {
              ConnectionStatus.setText("Client");
              clientClass = new ClientClass(groupOwnerAddress);
              clientClass.start();
          }
      }
  };
  

  And this is the code for the ServerThread, ClientThread and SendRecieveThread

  public class ServerClass extends Thread{
      Socket socket;
      ServerSocket serverSocket;
  
      @Override
      public void run() {
          try {
              serverSocket = new ServerSocket(8888);
              socket = serverSocket.accept();
              sendReceive = new SendReceive(socket);
              sendReceive.start();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  }
  
  private class SendReceive extends Thread {
      private Socket socket;
      private InputStream inputStream;
      private OutputStream outputStream;
  
      public SendReceive(Socket skt) {
          socket = skt;
          try {
              inputStream = socket.getInputStream();
              outputStream = socket.getOutputStream();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  
      @Override
      public void run() {
          byte[] buffer = new byte[1024];
          int bytes;
          while (socket!=null) {
              try {
                  bytes = inputStream.read(buffer);
                  if(bytes>0) {
                      handler.obtainMessage(MESSAGE_READ,bytes,-1,buffer).sendToTarget();
                  }
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }
  
      public void write(byte[] bytes) {
          try {
              outputStream.write(bytes);
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  }
  
  public class ClientClass extends Thread {
      Socket socket;
      String hostAdd;
      public ClientClass(InetAddress hostAddress) {
          hostAdd = hostAddress.getHostAddress();
          socket = new Socket();
      }
  
      @Override
      public void run() {
          try {
              socket.connect(new InetSocketAddress(hostAdd, 8888),1000);
              sendReceive = new SendReceive(socket);
              sendReceive.start();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  }
  

  The SendRecieve functionality gets invoked when a user clicks a send message button.

  btnSend.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
          String msg = writeMsg.getText().toString();
          sendReceive.write(msg.getBytes());
      }
  });
  

  I've run the app in USB-debugging mode using android studio and obtained the crash report from the adb logcat command:

  --------- beginning of crash
  03-27 22:16:54.115  6904  6904 E AndroidRuntime: FATAL EXCEPTION: main
  03-27 22:16:54.115  6904  6904 E AndroidRuntime: Process: june.androidapps.clatt, PID: 6904
  03-27 22:16:54.115  6904  6904 E AndroidRuntime: android.os.NetworkOnMainThreadException
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1318)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:111)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at java.net.SocketOutputStream.write(SocketOutputStream.java:145)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at june.androidapps.clatt.MainActivity$SendReceive.write(MainActivity.java:264)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at june.androidapps.clatt.MainActivity$5.onClick(MainActivity.java:135)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at android.view.View.performClick(View.java:5773)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at android.view.View$PerformClick.run(View.java:23035)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at android.os.Handler.handleCallback(Handler.java:836)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at android.os.Handler.dispatchMessage(Handler.java:103)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at android.os.Looper.loop(Looper.java:232)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at android.app.ActivityThread.main(ActivityThread.java:6802)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at java.lang.reflect.Method.invoke(Native Method)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1103)
  03-27 22:16:54.115  6904  6904 E AndroidRuntime:    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:964)
  03-27 22:17:06.089  7393  7393 E AndroidRuntime: FATAL EXCEPTION: main
  

  ...

  You can see the full log here https://drive.google.com/file/d/1CfKU5x2dQgkGBKHTvMywaNfPtMdCNEXG/view

  Can anyone please explain why the app behaves this way? I have gone through the entire logs for about an hour and I cant seem to find what's exactly going wrong in my code. Any help will be appreciated.

  with regards.
• I have been trying for the past week to get this to work routinely. My WifiP2P will sometimes work but it mostly crashes and I have no idea why

  So I'm just starting to learn how to connect two phones wirelessly over WifiP2p using my app.

  My app is a simple game of Rock, Paper, Scissors. Nothing overly complicated, and I'm trying to get the two test phones I'm using to "talk" to each other (example: one chooses rock, other chooses paper, and they update appropriately).

  My issue is that my app will constantly crash, or if I put in

      if (android.os.Build.VERSION.SDK_INT >= 23) {
              StrictMode.ThreadPolicy policy = new 
      StrictMode.ThreadPolicy.Builder().permitAll().build();
              StrictMode.setThreadPolicy(policy);
          }
  

  just to get it to run for testing purposes (I know the above stated code is a horrible idea), it will sometimes work, but mostly just crash.

  I also constantly keep getting the NetworkOnMainThreadException, which I thought I shouldn't since I extended the Thread class.

  So I've added in all the needed permissions

      <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
      <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
      <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
      <uses-permission android:name="android.permission.INTERNET" />
      <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
      <uses-permission 
      android:name="android.permission.ACCESS_COARSE_LOCATION"/>
      <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
  

  And I've tried creating "implements Runnable" methods to no avail. I considered using AsyncTask, but from what I've read, it'n not entirely the best choice, and also the android developers corner suggested using the Thread class for the simplicity of what I'm trying to do, which is essentially just sending a message from one phone to another.

  My code was created by following the tutorial from "Sarthi Technology", specifically this line of videos: https://www.youtube.com/watch?v=nw627o-8Fok&list=PLFh8wpMiEi88SIJ-PnJjDxktry4lgBtN3&index=1

  Still can't get anything working.

  I have two classes that are trying to run everything, a broadcast receiver class here:

  public class Wifi_P2P_Receiver extends BroadcastReceiver {
  
      private WifiP2pManager mManager;
      private WifiP2pManager.Channel mChannel;
      private MultiPlayer mActivity;
  
      public Wifi_P2P_Receiver(WifiP2pManager manager, WifiP2pManager.Channel channel, MultiPlayer mainActivity) {
          this.mManager = manager;
          this.mChannel = channel;
          this.mActivity = mainActivity;
      }
  
      @Override
      public void onReceive(Context context, Intent intent) {
          String action = intent.getAction();
  
          if(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
              int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
              if(state == WifiP2pManager.WIFI_P2P_STATE_ENABLED){
  //                Toast.makeText(context, "Wifi is ON", Toast.LENGTH_LONG).show();
              } else {
  //                Toast.makeText(context, "Wifi is OFF", Toast.LENGTH_LONG).show();
              }
          }
          if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {
              if(mManager != null) {
                  mManager.requestPeers(mChannel, mActivity.peerListListener);
              }
          }
          else if(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {
              if(mManager == null){
                  return;
              }
              NetworkInfo networkInfo = intent.getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO);
  
              if(networkInfo.isConnected()){
                  mManager.requestConnectionInfo(mChannel, mActivity.CIL);
              } else {
                  mActivity.status.setText("Device Disconnected");
              }
          }
          else if(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {
  
          }
      }
  }
  

  And then I have my main multiplayer class caller Multiplayer, which is very large so I'll break it up.

  Here's the first part up to the onCreate() method:

  public class MultiPlayer extends AppCompatActivity {
  
      Button btnDiscover;
      Button sendRock;
      Button sendPaper;
      Button sendScissors;
      String tempMsg = "";
      TextView status;
      TextView opponentChoice;
      TextView gameResult;
      String playerChoice = "";
      ListView playerList;
      WifiP2pManager mManager;
      WifiP2pManager.Channel mChannel;
      IntentFilter filter;
      Wifi_P2P_Receiver mReceiver;
      WifiManager wifi;
  
      List<WifiP2pDevice> peers = new ArrayList<WifiP2pDevice>();
      String[] deviceNameArray;
      WifiP2pDevice[] deviceArray;
  
      static final int MESSAGE_READ = 1;
  
      ServerClass serverClass;
      ClientClass clientClass;
      SendReceive sendReceive;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.connect);
  
          initialWork();
          exqListener();
      }
  

  initialWork() and exqListener() do all the main work. Here's initialWork():

  public void initialWork() {
          btnDiscover = (Button) findViewById(R.id.btnFindPlayers);
          playerList = (ListView) findViewById(R.id.listPlayerView);
  
          wifi = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
  
          mManager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
          mChannel = mManager.initialize(this, getMainLooper(), null);
  
          mReceiver = new Wifi_P2P_Receiver(mManager, mChannel, this);
  
          filter = new IntentFilter();
          filter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
          filter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
          filter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
          filter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
  
          sendRock = (Button) findViewById(R.id.btnSendRock);
          sendPaper = (Button) findViewById(R.id.btnSendPaper);
          sendScissors = (Button) findViewById(R.id.btnSendScissors);
      }
  

  And exqListener() handles all of the button presses (I have a button for Rock, Paper, and Scissors which sends a String "message" over the network):

  private void exqListener() {
          status = (TextView) findViewById(R.id.connectStatusTV);
          opponentChoice = (TextView) findViewById(R.id.opponentChoiceTV);
          gameResult = (TextView) findViewById(R.id.gameResultTV);
  
          btnDiscover = (Button) findViewById(R.id.btnFindPlayers);
          btnDiscover.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  mManager.discoverPeers(mChannel, new WifiP2pManager.ActionListener() {
                      @Override
                      public void onSuccess() {
  //                        Toast.makeText(getApplication(), "Discovery Started", Toast.LENGTH_LONG).show();
                          status.setText("Discovery Started");
                      }
  
                      @Override
                      public void onFailure(int i) {
  //                        Toast.makeText(getApplication(), "Discovery Failed", Toast.LENGTH_LONG).show();
                          status.setText("Discovery Failed");
                      }
                  });
              }
          });
  
          playerList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
              @Override
              public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                  final WifiP2pDevice device = deviceArray[i];
                  WifiP2pConfig config = new WifiP2pConfig();
                  config.deviceAddress = device.deviceAddress;
  
                  mManager.connect(mChannel, config, new WifiP2pManager.ActionListener() {
                      @Override
                      public void onSuccess() {
                          Toast.makeText(getApplication(), "Connected to " + device.deviceName, Toast.LENGTH_LONG).show();
                      }
  
                      @Override
                      public void onFailure(int i) {
                          Toast.makeText(getApplication(), "Not connected", Toast.LENGTH_LONG).show();
                      }
                  });
              }
          });
  
          sendRock.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  String msg = "Rock";
                  playerChoice = "Rock";
                  sendReceive.write(msg.getBytes());
                  if(tempMsg.length() > 0){
                      colorChange();
                  }
              }
          });
  
          sendPaper.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  String msg = "Paper";
                  playerChoice = "Paper";
                  sendReceive.write(msg.getBytes());
                  if(tempMsg.length() > 0){
                      colorChange();
                  }
              }
          });
  
          sendScissors.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  String msg = "Scissors";
                  playerChoice = "Scissors";
                  sendReceive.write(msg.getBytes());
                  if(tempMsg.length() > 0){
                      colorChange();
                  }
              }
          });
      }
  

  I have a listView that displays all nearby devices, which a user can connect to by item click. I also have a WifiP2pManager.ConnectionInfoListener and the appropriate methods for setting a user to host and another to client. These seem to be working so I won't paste the code in an effort to avoid as much clutter as possible. I also won't post the onResume() or onPause() methods as they are not an issue.

  I have a ServerClass, SendReceive, and ClientClass which are all subclasses of Multiplayer. Here's the ServerClass:

  public class ServerClass extends Thread {
  
          Socket socket;
          ServerSocket serverSocket;
  
          @Override
          public void run(){
              try {
                  serverSocket = new ServerSocket(8888);
                  socket = serverSocket.accept();
                  sendReceive = new SendReceive(socket);
                  sendReceive.start();
              } catch(IOException e) {
                  e.printStackTrace();
              }
          }
      }
  

  And my ClientClass:

  public class ClientClass extends Thread {
          Socket socket;
          String hostAdd;
  
          public ClientClass(InetAddress hostAddress){
              hostAdd = hostAddress.getHostAddress();
              socket = new Socket();
          }
  
          @Override
          public void run(){
  //            super.run();
              try {
                  socket.connect(new InetSocketAddress(hostAdd, 8888), 500);
                  sendReceive = new SendReceive(socket);
                  sendReceive.start();
              } catch(IOException e){
                  e.printStackTrace();
              }
          }
      }
  

  And finally the SendReceive subclass:

  private class SendReceive extends Thread {
          private Socket socket;
          private InputStream inputStream;
          private OutputStream outputStream;
  
          public SendReceive(Socket skt) {
              socket = skt;
              try {
                  inputStream = socket.getInputStream();
                  outputStream = socket.getOutputStream();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
  
          @Override
          public void run() {
  //            super.run();
              byte[] buffer = new byte[1024];
              int bytes;
  
              while(socket != null){
                  try {
                      bytes = inputStream.read(buffer);
                      if(bytes > 0){
                          handler.obtainMessage(MESSAGE_READ, bytes, -1, buffer).sendToTarget();
                      }
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              }
          }
  
          public void write(byte[] bytes){
              try {
                  outputStream.write(bytes);
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }
  

  One final thing I forgot to mention is my handler method, which is just part of the Multiplayer class by itself. So this is what I'm doing with the messages:

  Handler handler = new Handler(new Handler.Callback() {
          @SuppressLint("ResourceAsColor")
          @Override
          public boolean handleMessage(Message message) {
              switch(message.what){
                  case MESSAGE_READ:
                      byte[] readBuff = (byte[]) message.obj;
                      tempMsg = new String(readBuff, 0, message.arg1);
                      opponentChoice.setText("Your opponent chooses " + tempMsg + "!");
                      break;
              }
              return true;
          }
      });
  

  I believe that one of the main issues is the write(byte[] bytes) method, since every time I press one of the buttons, such as Rock, I get a NetworkOnMainThreadException, where the stackTrace points to the sendReceive.write(msg.getBytes()); line of the button's code. So I'm thinking it has somethign to do with the SendReceive class being on the main UI thread, which I thought it wouldn't be since I overrode the run() method when I had the subclass extend the Thread class.

  Any help would be greatly appreciated.
• Android NSD: registerService returns Port 0 and Host null

  I'm trying to connect two Android devices via Network Service Discovery API (NSD) in a network. I followed the official Android webpage during implementation. One of the devices acts as the server and the other acts as the client. I ask the network for the next free port. But as soon as I register the Server in the network via registerService(nsdsInfo, NsdManager.PROTOCOL_DNS_SD, mRegistrationListener) the parameters in nsdsInfo are empty. So before calling this line of code nsdsInfo object contains a correct port and a correct host etc. After calling this method the Callback method in the listener onServiceRegistered() contains Port = 0 and Host = null.

  Are there any guesses why the port and hostname is lost during registration process but the registrtation nevertheless successful? On the other side, the other device cannot discover the server, even if the registration callback "onServiceRegistrered()" is fired.

  Thanks in advance guys!

  //Const
      private static final String SERVICE_TYPE = "_speech._tcp";
      private static final String SERVICE_NAME = "speech";
  
      public WiFiServiceRegistry(Context ctx) throws IOException {
  
          this.context = ctx;
  
          initializeSocketAndPort();
          initializeNsdService();
          initializeRegistrationListener();
  
          if (nsdManager == null)
              nsdManager = (NsdManager) context.getSystemService(Context.NSD_SERVICE);
          System.out.println("nsdsinfo host" + nsdsInfo.getServiceName());
          System.out.println("nsdsinfo port" + nsdsInfo.getPort());
          nsdManager.registerService(nsdsInfo, NsdManager.PROTOCOL_DNS_SD, mRegistrationListener);
      }
  
      /**
       * Initializes the NsdServiceInfo.
       */
      private void initializeNsdService(){
          nsdsInfo = new NsdServiceInfo();
          nsdsInfo.setServiceName(SERVICE_NAME);
          nsdsInfo.setServiceType(SERVICE_TYPE);
          nsdsInfo.setPort(mLocalPort);
      }
  
      /**
       * Initializes the socket and port. Parameter 0 means that the next available port is used (dynamic).
       * @throws IOException
       */
      private void initializeSocketAndPort() throws IOException {
          mServerSocket = new ServerSocket(0);
          mLocalPort = mServerSocket.getLocalPort();
      }
  
      /**
       * Inizializes the registrationListener. Keeps track of the registration status.
       */
      private void initializeRegistrationListener(){
          mRegistrationListener = new NsdManager.RegistrationListener() {
              @Override
              public void onRegistrationFailed(NsdServiceInfo serviceInfo, int errorCode) {
                  System.out.println("WiFiServiceRegistry: Registration failed");
              }
  
              @Override
              public void onUnregistrationFailed(NsdServiceInfo serviceInfo, int errorCode) {
                  System.out.println("WiFiServiceRegistry: Unregistration failed");
              }
  
              @Override
              public void onServiceRegistered(NsdServiceInfo serviceInfo) {
                  System.out.println("WiFiServiceRegistry: Registered service");
                  System.out.println("WiFiServiceRegistry: Port " + serviceInfo.getPort());
                  System.out.println("WiFiServiceRegistry: Host " + serviceInfo.getHost());
                  System.out.println("WiFiServiceRegistry: ServiceName " + serviceInfo.getServiceName());
              }
  
              @Override
              public void onServiceUnregistered(NsdServiceInfo serviceInfo) {
                  System.out.println("WiFiServiceRegistry: Unregistered service");
              }
          };
      }
  
• Network Service Discovery not woking when app returns from AirPlane mode to Wifi during the running app

  I am having a problem related to Network Service Discovery.

  When I start the app with wifi connected, NSD Works Totally fine discovering the service and smoothly resolving them. But the problem arises when we connect wifi, after disabling wifi or switching the wifi from airplane mode.

  It just gets stuck on DiscoveryStarted and never proceeds from there, although it establishes the connection to the wifi router after turning off airplane mode.

  In code I have also ensured that the discovery will only start when the wifi connection is ensured but, no luck.

  Right now I have to kill the app in order for NSD to work properly.

  I am using NSD Helper from Google Gist:

  https://android.googlesource.com/platform/development/+/master/samples/training/NsdChat/src/com/example/android/nsdchat/NsdHelper.java

  NsdHelper helper;
      BroadcastReceiver wifiReciever = new BroadcastReceiver() {
          @Override
          public void onReceive(Context context, Intent intent) {
              final String action = intent.getAction();
              if (action.equals(WifiManager.SUPPLICANT_CONNECTION_CHANGE_ACTION)) {
                  if (intent.getBooleanExtra(WifiManager.EXTRA_SUPPLICANT_CONNECTED, false)) {
                      //do stuff
                      helper.stopDiscovery();
                      helper = new NsdHelper(context);
                      helper.discoverServices();
                  } else {
                      // wifi connection was lost
                      helper.stopDiscovery();
                  }
              }
          }
      };
  
  
  
  
      @Nullable
      @Override
      public IBinder onBind(Intent intent) {
          return null;
      }
  
      @Override
      public void onCreate() {
          super.onCreate();
          //startDiscovery();
  //        helper = new NsdHelper(this);
  //        helper.discoverServices();
  
          IntentFilter intentFilter = new IntentFilter();
          intentFilter.addAction(WifiManager.SUPPLICANT_CONNECTION_CHANGE_ACTION);
          registerReceiver(wifiReciever, intentFilter);
  
  
  
  
          Toast.makeText(this,"Service Started",Toast.LENGTH_SHORT).show();
      }
  
      @Override
      public void onDestroy() {
  //        if(service!= null)
  //        {
  //            service.stop();
  
  //        helper.stopDiscovery();
  //        }
          unregisterReceiver(wifiReciever);
  //
         Toast.makeText(this,"Service destroyed",Toast.LENGTH_SHORT).show();
          super.onDestroy();
      }
  
• NSDManager doesn't find services, only if searching for printers in standard app

  So, I hope I'm in the correct section since this is my first post.

  I have the following problem: I implemented a NSDManager after the example of this: https://github.com/ymitis/xamarin-android-nsd-chat I used his NSDHelper-class, and did everything else so it was fitting for my purpose.

  If I scan for services with this app, I don't find any of them. However, if I leave this application running, open notes and search for wireless printers, I suddenly find exactly these printers in my NSD-app. Seems like there is a core feature missing and I have no clue what it could be, since the git is working fine, but my app not.

  So for now, what I realised: When I start the phone, and the first thing I do is search for printers with a standard app, then starting my application, I find all services. But if I just start the device and then my app, I don't find any...

  My Code for my NSDHelper is the same as in here: https://github.com/ymitis/xamarin-android-nsd-chat/blob/master/XamarinAndroidNsdChatApp/XamarinAndroidNsdChatApp/NsdHelper.cs I just changed the servicename to search for.

  My Main Activity looks like this:

  using Android.App;
  using Android.Widget;
  using Android.OS;
  using System.Net.Sockets;
  using System.Net;
  using System.Threading.Tasks;
  using System.Linq;
  using System.Text;
  using Android.Net.Nsd;
  using Android.Content;
  using Android.Net.Wifi.P2p;
  using Android.Net.Wifi;
  using System.Threading;
  using Makaretu.Dns;
  using Orekaria.Lib.P2P;
  
  [assembly: UsesPermission(Android.Manifest.Permission.ChangeWifiMulticastState)]
  [assembly: UsesPermission(Android.Manifest.Permission.AccessWifiState)]
  [assembly: UsesPermission(Android.Manifest.Permission.AccessNetworkState)]
  [assembly: UsesPermission(Android.Manifest.Permission.ChangeWifiState)]
  [assembly: UsesPermission(Android.Manifest.Permission.Internet)]
  
  namespace NetworkDiscoveryTest
  {
     [Activity(Label = "NetworkDiscoveryTest", MainLauncher = true)]
     public class MainActivity : Activity
     {
  
        WifiManager wifi;
        WifiManager.MulticastLock mlock;
        static TextView console;
        NsdHelper nsd;
  
        protected override async void OnCreate(Bundle savedInstanceState)
        {
           base.OnCreate(savedInstanceState);
           SetContentView(Resource.Layout.Main);
  
           nsd = new NsdHelper(this);
           await Task.Run(new System.Action(Initialize));
  
  
           //Layout naming
           Button startButton = FindViewById<Button>(Resource.Id.startButton);
           Button endButton = FindViewById<Button>(Resource.Id.endButton);
           Button disButton = FindViewById<Button>(Resource.Id.disButton);
           console = FindViewById<TextView>(Resource.Id.console);
  
           startButton.Click += (s, args) => 
           {
              nsd.RegisterService(5353);
           };
  
           disButton.Click += (s, args) => 
           {
              nsd.DiscoverServices();
           };
  
           endButton.Click += (s, args) =>
           {
              nsd.StopDiscovery();
              nsd.TearDown();
           };
        }
  
        public void Initialize()
        {
           nsd.InitializeNsd();
        }
     }
  }
  

  I don't think that it's something really in the code, but maybe I'm missing a command for activating something?