ERROR: must implement OnFragmentInteractionListener

Question

It's trowing an error saying I must implment the OnFragmentInteractionListener, but as far as I'm aware I'm implementing it properly ... Any help would be greatly appreciated.

Main Activity

    import android.app.Activity; import android.app.FragmentManager; import android.app.FragmentTransaction; import android.os.Bundle;   public class MainActivity extends Activity implements NavFragment.OnFragmentInteractionListener, ContentFragment.OnFragmentInteractionListener{      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          FragmentManager fragmentManager = getFragmentManager();         FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();         fragmentTransaction.add(R.id.nav, new NavFragment());         fragmentTransaction.commit();          fragmentTransaction = fragmentManager.beginTransaction();         fragmentTransaction.add(R.id.content, new ContentFragment());         fragmentTransaction.commit();     }      @Override     public void onNavFragmentInteraction(String string) {         Bundle args = new Bundle();         args.putString("string", string);         ContentFragment content = new ContentFragment();         content.setArguments(args);          FragmentManager fragmentManager = getFragmentManager();         FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();          fragmentTransaction.addToBackStack(null);         fragmentTransaction.commit();     }      @Override     public void onContentFragmentInteraction(String string){      }  } 

NavFragment

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;  public class NavFragment extends Fragment implements View.OnClickListener {     private static final String ARG_PARAM1 = "param1";     private static final String ARG_PARAM2 = "param2";     private String mParam1;     private String mParam2;     private Button button;     private OnFragmentInteractionListener mListener;      public static NavFragment newInstance(String param1, String param2) {         NavFragment fragment = new NavFragment();         Bundle args = new Bundle();         args.putString(ARG_PARAM1, param1);         args.putString(ARG_PARAM2, param2);         fragment.setArguments(args);         return fragment;     }      public NavFragment() {      }      @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         if (getArguments() != null) {             mParam1 = getArguments().getString(ARG_PARAM1);             mParam2 = getArguments().getString(ARG_PARAM2);         }     }      @Override     public View onCreateView(LayoutInflater inflater, ViewGroup container,                              Bundle savedInstanceState) {          View v = inflater.inflate(R.layout.fragment_nav, container, false);          button = (Button) v.findViewById(R.id.submit);         button.setOnClickListener(this);          return v;     }      public void onButtonPressed(String string) {      }      @Override     public void onAttach(Activity activity) {         super.onAttach(activity);         try {             mListener = (OnFragmentInteractionListener) activity;         } catch (ClassCastException e) {             throw new ClassCastException(activity.toString()                     + " must implement OnFragmentInteractionListener");         }     }      @Override     public void onDetach() {         super.onDetach();         mListener = null;     }      @Override     public void onClick(View v) {         String string =  ((EditText) v.findViewById(R.id.gridSize)).toString();         mListener.onNavFragmentInteraction(string);     }      public interface OnFragmentInteractionListener {         public void onNavFragmentInteraction(String string);     }  } 

ContentFragment

import android.app.Activity; import android.app.Fragment; import android.net.Uri; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.GridView;   public class ContentFragment extends Fragment {     private static final String ARG_PARAM1 = "param1";     private static final String ARG_PARAM2 = "param2";     private String mParam1;     private String mParam2;     private OnFragmentInteractionListener mListener;      public static ContentFragment newInstance(String param1, String param2) {         ContentFragment fragment = new ContentFragment();         Bundle args = new Bundle();         args.putString(ARG_PARAM1, param1);         args.putString(ARG_PARAM2, param2);         fragment.setArguments(args);         return fragment;     }      public ContentFragment() {         // Required empty public constructor     }      @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         if (getArguments() != null) {             mParam1 = getArguments().getString(ARG_PARAM1);             mParam2 = getArguments().getString(ARG_PARAM2);         }     }      @Override     public View onCreateView(LayoutInflater inflater, ViewGroup container,                              Bundle savedInstanceState) {          View v = inflater.inflate(R.layout.fragment_content_fragmet, container, false);          String string = "1";          if (getArguments() != null) {             Bundle args = getArguments();             string = (String) args.get("string");         }         GridView gridView = (GridView) v.findViewById(R.id.gridview);          gridView.setNumColumns(Integer.parseInt(string));         gridView.setAdapter(new GridAdapter(this, Integer.parseInt(string)));          return v;     }      public void onButtonPressed(Uri uri) {      }      @Override     public void onAttach(Activity activity) {         super.onAttach(activity);         try {             mListener = (OnFragmentInteractionListener) activity;         } catch (ClassCastException e) {             throw new ClassCastException(activity.toString()                     + " must implement OnFragmentInteractionListener");         }     }      @Override     public void onDetach() {         super.onDetach();         mListener = null;     }      public interface OnFragmentInteractionListener {         public void onContentFragmentInteraction(String string);     } } 

error

03-02 18:46:47.254    1958-1958/com.peterchappy.lab5 E/AndroidRuntime﹕ FATAL EXCEPTION: main     Process: com.peterchappy.lab5, PID: 1958     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.peterchappy.lab5/com.peterchappy.lab5.MainActivity}: java.lang.ClassCastException: com.peterchappy.lab5.MainActivity@2298f3ca must implement OnFragmentInteractionListener         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)         at android.app.ActivityThread.access$800(ActivityThread.java:144)         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)         at android.os.Handler.dispatchMessage(Handler.java:102)         at android.os.Looper.loop(Looper.java:135)         at android.app.ActivityThread.main(ActivityThread.java:5221)         at java.lang.reflect.Method.invoke(Native Method)         at java.lang.reflect.Method.invoke(Method.java:372)         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)      Caused by: java.lang.ClassCastException: com.peterchappy.lab5.MainActivity@2298f3ca must implement OnFragmentInteractionListener         at com.peterchappy.lab5.ContentFragmet.onAttach(ContentFragmet.java:83)         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:853)         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)         at android.app.BackStackRecord.run(BackStackRecord.java:833)         at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452)         at android.app.Activity.performStart(Activity.java:5948)         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)             at android.app.ActivityThread.access$800(ActivityThread.java:144)             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)             at android.os.Handler.dispatchMessage(Handler.java:102)             at android.os.Looper.loop(Looper.java:135)             at android.app.ActivityThread.main(ActivityThread.java:5221)             at java.lang.reflect.Method.invoke(Native Method)             at java.lang.reflect.Method.invoke(Method.java:372)             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 

Answer 1

The OnFragmentInteractionListener interfaces in both of your Fragments contain a method with the same signature, and MainActivity is implementing one method to try to cover both interfaces.

Change the signature of one or both of the methods, then implement both methods in MainActivity. For example:

NavFragment

    public interface OnFragmentInteractionListener {         public void onNavFragmentInteraction(String string);     } 

ContentFragment

    public interface OnFragmentInteractionListener {         public void onContentFragmentInteraction(String string);     } 

MainActivity

    @Override     public void onNavFragmentInteraction(String string) {         // Do stuff     }      @Override     public void onContentFragmentInteraction(String string) {         // Do different stuff     }