El objeto de interfaz no funciona cuando se llama desde otro fragmento

Ok, así que tengo una aplicación de Android que básicamente es una entrada a un servidor node.js. La estructura de archivos consta de: MainActivity.java, FirstFragment.java, MiddleMan.java y MySocket.java.

MainActivity.java

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package ""; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.widget.EditText; import java.net.URISyntaxException; public class MainActivity extends Activity implements MiddleMan { String SERVER_ADDRESS = ""; MySocket my_socket; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); //noinspection SimplifiableIfStatement if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } public void onConnectButtonPressed(EditText editText_ID){ System.out.println("Received connect request from first fragment."); my_socket = new MySocket(); try { my_socket.EstablishConnection(SERVER_ADDRESS, editText_ID); } catch (URISyntaxException e) { e.printStackTrace(); } } public void ConnectionEstablished() { System.out.println("Received established connection from MySocket.java."); } } 

FirstFragment.java

 package ""; import android.app.Activity; import android.app.Fragment; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; public class FirstFragment extends Fragment{ MiddleMan mCallback; @Override public void onAttach(Activity activity){ super.onAttach(activity); try { mCallback = (MiddleMan) activity; } catch (ClassCastException e) { throw new ClassCastException(activity.toString() + " must implement ReqestConnect"); } } private static TextView textView_state; private static EditText editText_ID; Button button_connect; Button button_disconnect; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){ View view = inflater.inflate(R.layout.first_fragment_root,container,false); textView_state = (TextView) view.findViewById(R.id.textView_state); editText_ID = (EditText) view.findViewById(R.id.editText_ID); button_connect = (Button) view.findViewById(R.id.button_connect); button_connect.setOnClickListener(new View.OnClickListener(){ public void onClick(View v){ buttonConnectClicked(); } }); Button button_disconnect = (Button) view.findViewById(R.id.button_disconnect); return view; } private void buttonConnectClicked() { System.out.println("Connect Button Pressed "); mCallback.onConnectButtonPressed(editText_ID); } } 

MiddleMan.java

 package ""; import android.widget.EditText; public interface MiddleMan { void onConnectButtonPressed(EditText editText_ID); void ConnectionEstablished(); } 

MySocket.java

 package ""; import android.app.Activity; import android.app.Fragment; import android.widget.EditText; import com.github.nkzawa.emitter.Emitter; import com.github.nkzawa.socketio.client.IO; import com.github.nkzawa.socketio.client.Socket; import java.net.URISyntaxException; public class MySocket extends Fragment{ public Socket lobby; MiddleMan mCallBack; @Override public void onAttach(Activity activity){ super.onAttach(activity); try { mCallBack = (MiddleMan) activity; } catch (ClassCastException e) { throw new ClassCastException(activity.toString() + " must implement ReqestConnect"); } } public String getUserID(EditText editText_ID) { String string = editText_ID.getText().toString(); if (string.length() > 0) { return string; } else { return null; } } public void EstablishConnection(String SERVER_ADDRESS,EditText editText_ID) throws URISyntaxException { lobby = IO.socket(SERVER_ADDRESS); final String client = getUserID(editText_ID); System.out.println("client: " + client); lobby.on(Socket.EVENT_CONNECT, new Emitter.Listener() { @Override public void call(Object... args) { System.out.println("Connection established"); mCallBack.ConnectionEstablished(); } }).on("event", new Emitter.Listener() { @Override public void call(Object... args) { } }).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() { @Override public void call(Object... args) { System.out.println("Connection terminated."); } }); lobby.connect(); } } 

Hay un activity_main.xml, un first_fragment_root.xml (que se come toda la pantalla) y MySocket.java no tiene ningún diseño asociado.

Hasta ahora lo que ocurre es que la aplicación arranque muestra un editText, textview, y dos botones: conectar y desconectar. Al ingresar un ID y luego hacer clic en el botón de conectar ejecuta este bit de código en FirstFragment.java:

 private void buttonConnectClicked() { System.out.println("Connect Button Pressed "); mCallback.onConnectButtonPressed(editText_ID); } 

Que pasa a MiddleMan.java para que MainActivity.java ejecute este bit:

 public void onConnectButtonPressed(EditText editText_ID){ System.out.println("Received connect request from first fragment."); my_socket = new MySocket(); try { my_socket.EstablishConnection(SERVER_ADDRESS, editText_ID); } catch (URISyntaxException e) { e.printStackTrace(); } } 

Que lo envía a MySocket.java EstablishConnection:

 public void EstablishConnection(String SERVER_ADDRESS,EditText editText_ID) throws URISyntaxException { lobby = IO.socket(SERVER_ADDRESS); final String client = getUserID(editText_ID); System.out.println("client: " + client); lobby.on(Socket.EVENT_CONNECT, new Emitter.Listener() { @Override public void call(Object... args) { System.out.println("Connection established"); mCallBack.ConnectionEstablished(); } }).on("event", new Emitter.Listener() { @Override public void call(Object... args) { } }).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() { @Override public void call(Object... args) { System.out.println("Connection terminated."); } }); lobby.connect(); } 

Todo funcionó bien, hasta que añadí un poco sobre MySocket.java tener su propio objeto a Middle man para que pudiera decir MainActivity.java que está terminado. En lugar de ejecutar mCallBack.ConnectionEstablished (); El programa se rompe y me dice Attempt to invoke interface method 'void MiddleMan.ConnectionEstablished()' on a null object reference

No tengo ni idea de lo que estoy haciendo mal, supongo que el método onAttach en MySocket.java no es simplemente llamado así que el mCallBack aquí es nulo, pero ¿por qué? Gracias por leer.

Conclusión

He decidido publicar la versión de trabajo de este para ayudar a las personas que podrían tener el mismo problema o similar.

MainActivity.java

 package ""; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.widget.EditText; import java.net.URISyntaxException; public class MainActivity extends Activity implements MiddleMan { String SERVER_ADDRESS = ""; MySocket my_socket; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); //noinspection SimplifiableIfStatement if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } public void onConnectButtonPressed(EditText editText_ID){ if (my_socket==null) { System.out.println("Received connect request from first fragment."); my_socket = new MySocket(); my_socket.setListener(this); try { my_socket.EstablishConnection(SERVER_ADDRESS, editText_ID); } catch (URISyntaxException e) { e.printStackTrace(); } } } public void ConnectionEstablished() { System.out.println("Received established connection from MySocket.java."); System.out.println("Attempting to establish room for client."); my_socket.requestRoom(); runOnUiThread(new Runnable() { @Override public void run() { FirstFragment f = (FirstFragment) getFragmentManager().findFragmentById(R.id.first_fragment_root); f.updateTextViewState("Connected"); } }); } @Override public void onDisconnectButtonPressed() { if (my_socket!=null) { System.out.println("Received disconnect request from first fragment."); my_socket.requestDisconnect(); } } @Override public void DisconnectEstablished() { System.out.println("Received disconnected from MySocket.java."); my_socket = null; runOnUiThread(new Runnable() { @Override public void run() { FirstFragment f = (FirstFragment) getFragmentManager().findFragmentById(R.id.first_fragment_root); f.updateTextViewState("Disconnected"); } }); } } 

FirstFragment.java

 package ""; import android.app.Activity; import android.app.Fragment; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; public class FirstFragment extends Fragment{ MiddleMan mCallback; @Override public void onAttach(Activity activity){ super.onAttach(activity); try { mCallback = (MiddleMan) activity; } catch (ClassCastException e) { throw new ClassCastException(activity.toString() + " must implement ReqestConnect"); } } private static TextView textView_state; private EditText editText_ID; Button button_connect; Button button_disconnect; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){ View view = inflater.inflate(R.layout.first_fragment_root,container,false); textView_state = (TextView) view.findViewById(R.id.textView_state); editText_ID = (EditText) view.findViewById(R.id.editText_ID); button_connect = (Button) view.findViewById(R.id.button_connect); button_connect.setOnClickListener(new View.OnClickListener(){ @Override public void onClick(View v){ buttonConnectClicked(); } }); button_disconnect = (Button) view.findViewById(R.id.button_disconnect); button_disconnect.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { buttonDisconnectClicked(); } }); return view; } private void buttonDisconnectClicked() { System.out.println("Disconnect Button Pressed "); mCallback.onDisconnectButtonPressed(); } private void buttonConnectClicked() { System.out.println("Connect Button Pressed "); if (this.editText_ID.getText().toString()!=null && !this.editText_ID.getText().toString().isEmpty()) { mCallback.onConnectButtonPressed(editText_ID); } } public void updateTextViewState(String s){ textView_state.setText(s); } } 

MySocket.java

 package ""; import android.app.Fragment; import android.content.Context; import android.widget.EditText; import com.github.nkzawa.emitter.Emitter; import com.github.nkzawa.socketio.client.IO; import com.github.nkzawa.socketio.client.Socket; import java.net.URISyntaxException; public class MySocket extends Fragment{ public Socket lobby; String client; MiddleMan mCallBack; public void setListener(Context callback) { try { mCallBack = (MiddleMan) callback; } catch (ClassCastException e) { throw new ClassCastException(callback.toString() + " must implement ReqestConnect"); } } public String getUserID(EditText editText_ID) { String string = editText_ID.getText().toString(); if (string.length() > 0) { return string; } else { return null; } } public void EstablishConnection(String SERVER_ADDRESS,EditText editText_ID) throws URISyntaxException { lobby = IO.socket(SERVER_ADDRESS); final String client = getUserID(editText_ID); this.client = client; System.out.println("client: " + this.client); lobby.on(Socket.EVENT_CONNECT, new Emitter.Listener() { @Override public void call(Object... args) { System.out.println("Connection established"); mCallBack.ConnectionEstablished(); } }).on("event", new Emitter.Listener() { @Override public void call(Object... args) { String s = (String) args[0]; System.out.println(s); } }).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() { @Override public void call(Object... args) { System.out.println("Connection terminated."); if (lobby!=null) { Disconnect(); } } }).on("room_created", new Emitter.Listener() { @Override public void call(Object... args) { String s = (String) args[0]; System.out.println(s); } }); lobby.connect(); } public void requestRoom() { lobby.emit("request_user_room", this.client); } public void requestDisconnect() { if (lobby!=null) { if (lobby.connected()) { lobby.disconnect(); } } } private void Disconnect() { lobby.off(Socket.EVENT_CONNECT); lobby.off("event"); lobby.off(Socket.EVENT_DISCONNECT); lobby.off("room_created"); lobby = null; mCallBack.DisconnectEstablished(); } } 

MiddleMan.java

 package ""; import android.widget.EditText; public interface MiddleMan { void onConnectButtonPressed(EditText editText_ID); void ConnectionEstablished(); void onDisconnectButtonPressed(); void DisconnectEstablished(); } 

Activity_main.xml

 <RelativeLayout 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" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"> <fragment android:layout_width="match_parent" android:layout_height="match_parent" android:name="<<PATH_TO_>>.FirstFragment" android:id="@+id/first_fragment_root" tools:layout="@layout/first_fragment_root"/> </RelativeLayout> 

First_fragment_root.xml

 <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceMedium" android:text="@string/textView_ID" android:id="@+id/textView_ID" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:layout_marginTop="23dp" /> <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:inputType="phone" android:ems="10" android:id="@+id/editText_ID" android:hint="@string/editText_ID" android:layout_marginLeft="23dp" android:layout_marginStart="23dp" android:layout_alignBottom="@+id/textView_ID" android:layout_toRightOf="@+id/textView_ID" android:layout_toEndOf="@+id/textView_ID" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceMedium" android:text="@string/textView_status" android:id="@+id/textView_status" android:layout_alignParentBottom="true" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceMedium" android:text="@string/textView_state" android:id="@+id/textView_state" android:layout_alignParentBottom="true" android:layout_toRightOf="@+id/textView_status" android:layout_marginLeft="23dp" android:layout_marginStart="23dp" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/button_connect" android:id="@+id/button_connect" android:layout_below="@+id/textView_ID" android:layout_alignLeft="@+id/editText_ID" android:layout_alignStart="@+id/editText_ID" android:layout_marginTop="25dp" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/button_disconnect" android:id="@+id/button_disconnect" android:layout_alignBottom="@+id/button_connect" android:layout_alignRight="@+id/editText_ID" android:layout_alignEnd="@+id/editText_ID" /> </RelativeLayout> 

 onAttach(Context context) Called when a fragment is first attached to its context. 

 @Override public void onAttach(Activity activity){ super.onAttach(activity); try { mCallBack = (MiddleMan) activity; } catch (ClassCastException e) { throw new ClassCastException(activity.toString() + " must implement ReqestConnect"); } } 

 public void setListener(ReqestConnect callback) { mCallBack = callback; } 

 public void onConnectButtonPressed(EditText editText_ID){ System.out.println("Received connect request from first fragment."); my_socket = new MySocket(); my_socket.setListener(this); try { my_socket.EstablishConnection(SERVER_ADDRESS, editText_ID); } catch (URISyntaxException e) { e.printStackTrace(); } }