多项选择列表视图不显示所有对象

我正在学习一个关于android中的多项选择列表视图的教程。

我想知道那个问题的原因在哪里。

这是MainActivity类的代码:

public class MainActivity extends AppCompatActivity {

    Toolbar toolbar;
    FloatingActionButton fab;
    ListView list;
    TextView txt_menu;
    String dipilih;
    private static final String TAG = MainActivity.class.getSimpleName();

    Adapter adapter;
    ProgressDialog pDialog;

    List<Data> itemList = new ArrayList<Data>();

    // Sesuaikan dengan IP Address PC/LAptop atau ip emulator bawaan android 10.0.2.2
    private static String url = "https://.../test/menu.php";

    public static final String TAG_NAMA = "nama";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        fab     = (FloatingActionButton) findViewById(R.id.fab);
        list    = (ListView) findViewById(R.id.list_menu);

        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String checkbox = "";
                for (Data hold : adapter.getAllData()) {
                    if (hold.isCheckbox()) {
                        checkbox += "\n" + hold.getMenu();
                    }
                }
                if (!checkbox.isEmpty()) {
                    dipilih = checkbox;
                } else {
                    dipilih = "Anda Belum Memilih Menu.";
                }

                formSubmit(dipilih);
            }
        });

        callVolley();

        adapter = new Adapter(this, (ArrayList<Data>) itemList);
        list.setAdapter(adapter);

        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                adapter.setCheckBox(position);
            }
        });

    }

    private void formSubmit(String hasil){
        AlertDialog.Builder dialog = new AlertDialog.Builder(this);
        LayoutInflater inflater = getLayoutInflater();
        View dialogView = inflater.inflate(R.layout.form_submit, null);
        dialog.setView(dialogView);
        dialog.setIcon(R.mipmap.ic_launcher);
        dialog.setTitle("Menu Yang Dipilih");
        dialog.setCancelable(true);

        txt_menu = (TextView) dialogView.findViewById(R.id.txt_menu);

        txt_menu.setText(hasil);

        dialog.setNeutralButton("CLOSE", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });

        dialog.show();
    }

    private void callVolley(){
        itemList.clear();
        // menapilkan dialog loading
        pDialog = new ProgressDialog(this);
        pDialog.setMessage("Loading...");
        showDialog();

        // membuat request JSON
        JsonArrayRequest jArr = new JsonArrayRequest(url, new Response.Listener<JSONArray>() {
                    @Override
                    public void onResponse(JSONArray response) {
                        Log.d(TAG, response.toString());
                        hideDialog();

                        // Parsing json
                        for (int i = 0; i < response.length(); i++) {
                            try {
                                JSONObject obj = response.getJSONObject(i);

                                Data item = new Data();

                                item.setMenu(obj.getString(TAG_NAMA));

                                // menambah item ke array
                                itemList.add(item);
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                        }

                        // notifikasi adanya perubahan data pada adapter
                        adapter.notifyDataSetChanged();
                    }
                }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                VolleyLog.d(TAG, "Error: " + error.getMessage());
                hideDialog();
            }
        });

        // menambah request ke request queue
        AppController.getInstance().addToRequestQueue(jArr);
    }

    private void showDialog() {
        if (!pDialog.isShowing())
            pDialog.show();
    }

    private void hideDialog() {
        if (pDialog.isShowing())
            pDialog.dismiss();
    }

}

这是适配器类:

public class Adapter extends BaseAdapter {

    private Context activity;
    private ArrayList<Data> data;
    private static LayoutInflater inflater = null;
    private View vi;
    private ViewHolder viewHolder;

    public Adapter(Context context, ArrayList<Data> items) {
        this.activity = context;
        this.data = items;
        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public int getCount() {
        return data.size();
    }

    @Override
    public Object getItem(int i) {
        return i;
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(int position, View view, ViewGroup viewGroup) {
        vi = view;
        final int pos = position;
        Data items = data.get(pos);

        if(view == null) {
            vi = inflater.inflate(R.layout.list_row, null);
            viewHolder = new ViewHolder();
            viewHolder.checkBox = (CheckBox) vi.findViewById(R.id.cb);
            viewHolder.menu = (TextView) vi.findViewById(R.id.nama_menu);
            vi.setTag(viewHolder);
        }else {
            viewHolder = (ViewHolder) view.getTag();
            viewHolder.menu.setText(items.getMenu());
        }

        if(items.isCheckbox()){
            viewHolder.checkBox.setChecked(true);
        } else {
            viewHolder.checkBox.setChecked(false);
        }

        return vi;
    }

    public ArrayList<Data> getAllData(){
        return data;
    }

    public void setCheckBox(int position){
        Data items = data.get(position);
        items.setCheckbox(!items.isCheckbox());
        notifyDataSetChanged();
    }

    public class ViewHolder{
        TextView menu;
        CheckBox checkBox;
    }
}

首次发射

单击listview后