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

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• Android PDF Viewer null object reference error

  I am using barteksc Android PDF Viewer like many others (https://github.com/barteksc/AndroidPdfViewer). I keep receiving a null object reference error. This is the error.

  E/AndroidRuntime: FATAL EXCEPTION: main
                    Process: group6.interactivehandwriting, PID: 24037
                    java.lang.RuntimeException: Unable to start activity ComponentInfo{group6.interactivehandwriting/group6.interactivehandwriting.activities.RoomActivity.RoomActivity}: android.view.InflateException: Binary XML file line #9: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
  

  I have checked to make sure I am referencing the views correctly. The asset I am loading called "sample.pdf" is in my assets.

  * Can you see any reason why I am receiving this error? *

  I realize there are multiple post about this library, however every instance seems to be unique so I decided to go ahead and ask.

  RoomActivity.java

  package group6.interactivehandwriting.activities.RoomActivity;
  
  import android.content.res.AssetManager;
  import android.os.Bundle;
  import android.app.Activity;
  import android.util.Log;
  import android.view.View;
  
  import com.github.barteksc.pdfviewer.PDFView;
  import com.github.barteksc.pdfviewer.listener.OnLoadCompleteListener;
  import com.github.barteksc.pdfviewer.listener.OnPageChangeListener;
  import com.github.barteksc.pdfviewer.scroll.DefaultScrollHandle;
  
  import group6.interactivehandwriting.R;
  import group6.interactivehandwriting.activities.RoomActivity.views.DocumentView;
  import group6.interactivehandwriting.activities.RoomActivity.views.RoomView;
  
  public class RoomActivity extends Activity implements OnPageChangeListener, OnLoadCompleteListener {
      RoomView roomView;
      DocumentView docView;
      PDFView pView;
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          Log.d("Android: ", "Setting content view to an instance of RoomView in: " + this.getClass().getName());
          setContentView(R.layout.activity_draw);
  
          System.out.println("Attempting to set ImageView..");
          pView = (PDFView) findViewById(R.id.pdfView);
          pView.fromAsset("sample.pdf").defaultPage(0)
                  .enableSwipe(true).swipeHorizontal(false).
                  onPageChange(this).enableAnnotationRendering(true).onLoad(this).scrollHandle(new DefaultScrollHandle(this)).load();
  
  
      }
  
      @Override
      public void onPageChanged(int page, int pageCount) {
          setTitle(String.format("%s %s / %s", "Sample", page + 1, pageCount));
      }
  
      @Override
      public void loadComplete(int nbPages) {
      }
  }
  

  AndroidManifest.xml

  <?xml version="1.0" encoding="utf-8"?>
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="group6.interactivehandwriting">
  
      <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
      <application
          android:allowBackup="true"
          android:icon="@mipmap/ic_launcher"
          android:label="@string/app_name"
          android:roundIcon="@mipmap/ic_launcher_round"
          android:supportsRtl="true"
          android:theme="@style/AppTheme">
          <activity
              android:name=".activities.RoomActivity.RoomActivity"
              android:label="@string/title_activity_menu"
              android:theme="@style/AppTheme.NoActionBar">
              <intent-filter>
                  <action android:name="android.intent.action.MAIN" />
  
                  <category android:name="android.intent.category.LAUNCHER" />
              </intent-filter>
          </activity>
      </application>
  
  </manifest>
  

  activity_draw.xml

  <?xml version="1.0" encoding="utf-8"?>
  <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".activities.RoomActivity.RoomActivity">
  
      <view
          android:id="@+id/room_view"
          id="@+id/view"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          app:layout_constraintBottom_toBottomOf="parent"
          app:layout_constraintEnd_toEndOf="parent"
          app:layout_constraintStart_toStartOf="parent"
          app:layout_constraintTop_toTopOf="parent" />
  
      <com.github.barteksc.pdfviewer.PDFView
          android:id="@+id/pdfView"
          android:layout_width="match_parent"
          android:layout_height="match_parent"/>
  
      <TextView
          android:id="@+id/textView"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginStart="8dp"
          android:layout_marginTop="8dp"
          android:text="@string/room"
          app:layout_constraintStart_toStartOf="parent"
          app:layout_constraintTop_toTopOf="parent" />
  
  </android.support.constraint.ConstraintLayout>
  

  Dependencies:

  compile 'com.github.barteksc:android-pdf-viewer:2.8.2'
  
  compile 'org.apache.commons:commons-collections4:4.1'
  
• Trying to fit the settings activity in a fragment window - Android Studio

  I am working on an app and something troubles me, I want to create a settings activity in a fragment layout and the thing is that if I create a settings activity from the android studio's menu (this), there's no way that I can transform it into a fragment. I want to make it be this way (photo) .

  The thing is that when i change fragments, i use theFragment = new fragment_body();, where it is public class fragment_body extends Fragment, with its onCreateView of:

  public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
          return inflater.inflate(R.layout.view_settings, null);
      }
  

  where on the settings activity i don't have any of these things, i've tried multiple things but i don't know how to do it. Where the settings activity is: public class SettingsActivity extends PreferenceActivity. Please guide me of how to do this, Thanks in advance.
• Exception: com.android.volley.AuthFailureError is never thrown in the method

  I am using volley. In there I have added a method getParams. But AuthFailureError is getting grayed, when I type "return params" in the body. Due to which I am unable to save data in the database. I am wamp server. I have googled a lot but no luck.

  
• How do I connect raspberry pi(Slave) to a single android device(Master) with WIFI Direct/P2P

  How do you connect a raspberry pi(slave) to a single android device(master)? I've seen the other way round android device to raspberry pi but wasn't able to find raspberry pi -> android device.
• Data Transferring on WiFi P2P

  Are there any way excludes the Socket for data transferring on the WiFi P2P connection? Something like Volley library?

  I watched Sarthi Technology | Android WiFi Direct Tutorial but it uses theSocket, are there any other way for it?

  And I searched web but no thing found ...
• When we need to a socket connect is an Android app

  What is the socket and when we need to it in an Android app? Is it just for peer-to-peer data transferring or it is necessary for networking too? Can we transfer data in WiFiP2P without that?

  I watched Sarthi Technology | Android WiFi Direct Tutorial but I can't understand what is our need to that.
• Android NSD DiscoveryListener no service found behaviour

  I was using the NsdManager to discover and resolve WIFI services. Untill there are some services found, no problem, but how can i handle the situation when no services found, i need to perform some action also on this event. Instead i get a UI crash since the listener already exist. I'm doing mNsdManager.stopServiceDiscovery(mDiscoveryListener); when the service is found but how can i stop it if there is no services found? Is there any way to handle this situation? Thanks a lot in advance, Liudmila
• How to scan all Device Connected to wifi in android accurately?

  Hi i am trying to find all devices connected to My WIFI Router from android and ,i need to device Mac address and local ip address of each device , right now , i am trying to find from ARP cache table . but sometime in the scan some devices are missing , it is not so accurate .

  My Code :

   List<LocalDeviceInfo> devicesInfos = new ArrayList<>();
  
  
          BufferedReader bufferedReader = null;
  
          try {
              bufferedReader = new BufferedReader(new FileReader("/proc/net/arp"));
  
              String line;
              while ((line = bufferedReader.readLine()) != null) {
                  String[] splitted = line.split(" +");
                  if (splitted != null && splitted.length >= 4) {
                      String ip = splitted[0];
                      String mac = splitted[3];
                      if (mac.matches("..:..:..:..:..:..")) {
                          LocalDeviceInfo thisNode = new LocalDeviceInfo(ip, mac);
                          devicesInfos.add(thisNode);
                      }
                  }
              }
  
          } catch (FileNotFoundException e) {
              e.printStackTrace();
          } catch (IOException e) {
              e.printStackTrace();
          } finally{
              try {
                  bufferedReader.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
  
          // Print Description
          for (LocalDeviceInfo devicesInfo :devicesInfos)
          {
              System.out.print("✅");
              System.out.println("IP : "+devicesInfo.getIp());
              System.out.println("Mac : "+devicesInfo.getMacAddress());
          }
  

  ---

  How can i scan all devices (IP address and Mac address) in android accurately .

  ---
• Network Service Discovery: empty NsdServiceInfo in onServiceRegistered()-Callback of the RegistrationListener

  When I register a service, following the guidelines from android developers, the NsdServiceInfo-Object does not contain all the information it should contain after the service was registered.

  mRegistrationListener = new NsdManager.RegistrationListener() {
  
    @Override
    public void onServiceRegistered(NsdServiceInfo _NsdServiceInfo) {
    Log.i(TAG, "Service registered: "+_NsdServiceInfo);
    }
  
  [...]
  
  }
  

  So when the onServiceRegistered()-callback is fired (that should only be, if the service was successfully registered) the log-message says:

  Service registered: name: LTCServer_Niklas' Galaxy A3, type: null, host: null, port: 0, txtRecord: 
  

  So the, for the registration inserted, type (-http.-tcp.) was deleted and there is no host or port in the _NsdServiceInfo. This could not be correct.

  This happens on various devices with various android-versions.

  Does someone have an explanation about this?