Java.Lang.Classcastexception: Activity Cannot Be Cast to Adapter While Trying to Convert Activity to Fragment

java.lang.ClassCastException: Activity cannot be cast to Adapter while trying to convert Activity to Fragment

Thanks to what Mike M. and Reza.Abedini said among answers and comments I was able to understand what was happening and to overcome this issue.

The problem was in the Adapter that was prepared to get Context from Activity so I had to convert the parameter to Fragment and it ended up working like this:

public NotesAdapter(List<Note> list, RoomMarkdownActivity fragment) {
    this.layoutInflater = LayoutInflater.from(fragment.getActivity());
    this.list = list;
    this.fragment = fragment;
    this.onNoteItemClick = fragment;
}

And the Fragment like:

public class RoomMarkdownActivity extends Fragment implements NotesAdapter.OnNoteItemClick {

    public static RoomMarkdownActivity newInstance() {
        return new RoomMarkdownActivity();
    }

    RecyclerView recyclerView;
    TextView textViewMsg;
    NoteDatabase noteDatabase;
    List<Note> notes;
    NotesAdapter notesAdapter;
    int pos;

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.room_markdown_activity, container, false);
        textViewMsg = view.findViewById(R.id.textview_empty);
        FloatingActionButton fab = view.findViewById(R.id.fab);
        fab.setOnClickListener(listener);
        recyclerView = view.findViewById(R.id.recycler_view);
        initializeViews();
        displayList();
        return view;
    }

    private void displayList() {
        noteDatabase = NoteDatabase.getInstance(getActivity());
        new RetrieveTask(this).execute();
    }

    private static class RetrieveTask extends AsyncTask<Void, Void, List<Note>> {

        private WeakReference<RoomMarkdownActivity> activityReference;

        RetrieveTask(RoomMarkdownActivity context) {
            activityReference = new WeakReference<>(context);
        }

        @Override
        protected List<Note> doInBackground(Void... voids) {
            if (activityReference.get() != null)
                return activityReference.get().noteDatabase.getNoteDao().getNotes();
            else
                return null;
        }

        @Override
        protected void onPostExecute(List<Note> notes) {
            if (notes != null && notes.size() > 0) {
                activityReference.get().notes.clear();
                activityReference.get().notes.addAll(notes);
                activityReference.get().textViewMsg.setVisibility(View.GONE);
                activityReference.get().notesAdapter.notifyDataSetChanged();
            }
        }
    }

    public void initializeViews() {
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        notes = new ArrayList<>();
        notesAdapter = new NotesAdapter(notes, this);
        recyclerView.setAdapter(notesAdapter);
    }

    private View.OnClickListener listener = new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            startActivityForResult(new Intent(getActivity(), RoomMarkdownAddNoteActivity.class), 100);
        }
    };

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == 100 && resultCode > 0) {
            if (resultCode == 1) {
                notes.add((Note) data.getSerializableExtra("note"));
            } else if (resultCode == 2) {
                notes.set(pos, (Note) data.getSerializableExtra("note"));
            }
            listVisibility();
        }
    }

    @Override
    public void onNoteClick(final int pos) {
        new AlertDialog.Builder(getActivity())
                .setTitle("Select:")
                .setItems(new String[]{"Read", "Update", "Delete"}, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        switch (i) {
                            case 0:
                                RoomMarkdownActivity.this.pos = pos;
                                startActivityForResult(
                                        new Intent(getActivity(),
                                                RoomMarkdownViewNoteActivity.class).putExtra(
                                                "note", notes.get(pos)), 100);
                                break;
                            case 1:
                                RoomMarkdownActivity.this.pos = pos;
                                startActivityForResult(
                                        new Intent(getActivity(),
                                                RoomMarkdownAddNoteActivity.class).putExtra(
                                                "note", notes.get(pos)), 100);
                                break;
                            case 2:
                                noteDatabase.getNoteDao().deleteNote(notes.get(pos));
                                notes.remove(pos);
                                listVisibility();
                                break;
                        }
                    }
                }).show();
    }

    public void listVisibility() {
        int emptyMsgVisibility = View.GONE;
        if (notes.size() == 0) {
            if (textViewMsg.getVisibility() == View.GONE)
                emptyMsgVisibility = View.VISIBLE;
        }
        textViewMsg.setVisibility(emptyMsgVisibility);
        notesAdapter.notifyDataSetChanged();
    }

    @Override
    public void onDestroy() {
        noteDatabase.cleanUp();
        super.onDestroy();
    }

}

Thank you very much for the help and I hope this question/answer helps others as well!

ClassCastException: MainActivity cannot be cast to Listener

One thing is the context and another is the WifiScanner.Listener. Your ScanCollector needs both so pass both of them:

public ScanCollector(Context context, WifiScanner.Listener listener) {
    if (context == null)
        throw new NullPointerException();
    this.context = context;
    this.listener = listener
}

And when you create it:

sc = new ScanCollector(getActivity(), this);

Android Activity to Fragment: Replacing this with getActivity() throws error: ClassCastException

It's because you're expecting TaskRowListener inside your TaskAdapter class:

class TaskAdapter(context: Context, taskList: MutableList<Task>) : BaseAdapter() {

    ..
     // here you're expecting a TaskRowListener
     var _rowListener: TaskRowListener = context as TaskRowListener

.........
}

but you're activity isn't a TaskRowListener. So, you need to modify your activity to implement TaskRowListener with something like this:

class ToDoActivity : FragmentActivity(), TaskRowListener {
  ...
}

Although I think that you should not use activity at all to keep the Adapter handled only by the TodoFragment and keep using:

_adapter = TaskAdapter(this, _taskList!!)

java.lang.ClassCastException: com.example.readdoang.ui.login_regist_activity.LoginRegistActivity cannot be cast to com

in your class RegisterFragment,override the onCreateView(), in this method you can pass your view(fragment) to presenter like this :

presenter =  RegisterPresenter(this)

and your presenter should like this :

class RegisterPresenter(internal val view: RegisterView.View) : RegisterView.Presenter

SimpleCursorAdapter ClassCastException in fragment

myAdapter = (MyAdapter) new
SimpleCursorAdapter(getActivity(),R.layout.carerrow , cursor, from,
to);

Just replace SimpleCursorAdapter with MyAdapter...

Also, you could use support v4 library to get loaders on pre-honeycomb devices.

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