Using Fragments on Android

Question

I've done a few simple apps, but still new to Android development. I've been trying to make fragments work but my app just seems to crash every time I try to load a fragment. I'm trying to make a game. The way I had structured it was that every menu screen would be a fragment(main menu, options, ingame). I went on and made my research about how to program a fragment. Found a few good articles and videos. Pretty much they all do kinda the same thing, but for them it seems to work. It really didn't work for me. They way I wanted this to work was, load one activity and on that activity change or replace fragments according to the menu.

On crash, logcat, sometimes displays the error and sometimes it doesn't.

Let me know if you need the XML file(highly doubt it. Not adding fragment with fragment tag).

This is what I've tried so far:

MainActivity:

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);

        FragmentManager fragmentManager = getFragmentManager();

        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

        BlankFragment blankFragment= new BlankFragment();

        fragmentTransaction.add(android.R.id.content,blankFragment);

        fragmentTransaction.commit();   

    }
}

BlankFragment:

private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    private static Button startBtn,
    optionsBtn;

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

    // TODO: Rename and change types and number of parameters
    public static BlankFragment newInstance(String param1, String param2) {
        BlankFragment fragment = new BlankFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    public BlankFragment() {
        // 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  view = inflater.inflate(R.layout.fragment_blank, container, false);

        // Inflate the layout for this fragment
        return view;
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(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 onFragmentInteraction(Uri uri);
    }

LogCat:

07-07 23:03:20.120    8978-8978/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.marybel.myapplication, PID: 8978
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.marybel.myapplication/com.example.marybel.myapplication.MainActivity}: java.lang.ClassCastException: com.example.marybel.myapplication.MainActivity@3275aea8 must implement OnFragmentInteractionListener
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5021)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.ClassCastException: com.example.marybel.myapplication.MainActivity@3275aea8 must implement OnFragmentInteractionListener
            at com.example.marybel.myapplication.BlankFragment.onAttach(BlankFragment.java:83)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:849)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
            at android.app.BackStackRecord.run(BackStackRecord.java:684)
            at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1447)
            at android.app.Activity.performStart(Activity.java:5240)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2168)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5021)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
            at dalvik.system.NativeStart.main(Native Method)

Any explanation and suggestions would be greatly appreciated, thanks.

Answer 1

Managed to get it working, they way I added the fragment was by right clicking on Layout>New>Fragment. Seem like one of the auto generated methods or overrides made it crash. Deleted everything except the OnCreateView and worked just fine. Thanks

Answer 2

On a first glimpse I see in Activity > onCreate() your setContentView()is commented.

For adding any fragment into your activity, first thing beforehand is setting the activity view by calling setContentView().

Please move setContentView() after super.onCreate(savedInstanceState) and let know how is then, e.g.

@Override
protected void onCreate(Bundle bundle) {
    super.onCreate(bundle);

    setContentView(R.layout.YOUR_LAYOUT_FILE_NAME);
    ...
}