title: ERROR: must implement OnFragmentInteractionListener
body: <p>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.</p>
  
  <p>Main Activity</p>
  
  <pre><code>    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){
  
      }
  
  }
  </code></pre>
  
  <p>NavFragment</p>
  
  <pre><code>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);
      }
  
  }
  </code></pre>
  
  <p>ContentFragment</p>
  
  <pre><code>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);
      }
  }
  </code></pre>
  
  <p>error</p>
  
  <pre><code>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)
  </code></pre>