How to get the checkbox checked value in the listview?

I'm having requirement where i need to get the checkbox value count when i press a button. If the count is greater than 0 then i need to do some operations. I'm trying to do as below. checkbox is in listview which extends baseadapter.

Below is my adpater which extends baseapdater

public class PreferencesSyncAdapter extends BaseAdapter {
        private Context context;
        private LayoutInflater mInflater;

        public PreferencesSyncAdapter(Context context) {
            this.context = context;
            // Cache the LayoutInflate to avoid asking for a new one each time.
            mInflater = LayoutInflater.from(context);
        }

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

        @Override
        public Object getItem(int arg0) {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public long getItemId(int arg0) {
            // TODO Auto-generated method stub
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            SyncPreferenceItem syncCatItem = syncListItems.get(position);
            ISyncCategoryEnum test = syncCatItem.getSyncCategory();
            boolean isChecked = test.isSyncEnabled(this.context);

            // A ViewHolder keeps references to children views to avoid unneccessary calls
            // to findViewById() on each row.
            ViewHolder holder;

            // When convertView is not null, we can reuse it directly, there is no need
            // to reinflate it. We only inflate a new View when the convertView supplied
            // by ListView is null.
            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.list_item_preferences_sync, null);
                // Creates a ViewHolder and store references to the two children views
                // we want to bind data to.
                holder = new ViewHolder();
                holder.syncItemTV = (TextView) convertView.findViewById(R.id.syncItemTV);
                holder.syncStatusTV = (TextView) convertView.findViewById(R.id.syncStatusTV);
                holder.syncItemIV = (ImageView) convertView.findViewById(R.id.syncItemIV);
                holder.syncCB = (CheckBox) convertView.findViewById(R.id.syncCB);
                holder.progressBar = (ProgressBar) convertView.findViewById(R.id.progress_spinner);

                holder.syncCB.setChecked(isChecked);
                setCheckBox(holder, isChecked);

                convertView.setTag(holder);
            } else {
                // Get the ViewHolder back to get fast access to the TextView
                // and the ImageView.
                holder = (ViewHolder) convertView.getTag();
                holder.syncCB.setChecked(isChecked);
                setCheckBox(holder, isChecked);
            }
            if (convertView == null) return convertView;
            //CheckBox cb = (CheckBox) convertView.findViewById(R.id.custCB);
            holder.syncCB.setOnClickListener(new DefaultOnClickListener(this.context, syncCatItem, holder));

            // Bind the data efficiently with the holder.
            //holder.custNameTV.setText(ReturnCustomerFilter.mAttributesArray[position]);

            holder.syncItemTV.setText(syncCatItem.getStrRes());
            SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm");
            /*Date lastSyncDate = syncCatItem.getSyncCategory().getLastSyncTime();
            Calendar cal = Calendar.getInstance();
            cal.setTime(lastSyncDate);
            //sdf.setCalendar(cal);
            Calendar syncTimeCal = DateUtil.convertTimeToLocal(TimeZone.getDefault(), cal);
            sdf.setCalendar(syncTimeCal);*/
            holder.syncStatusTV.setText(this.context.getResources().getString(R.string.sync_progress_last_synchronized) +
                    " : " + sdf.format(new Date(syncCatItem.getSyncCategory().getLastSyncTime(PreferencesSync.this.mContext))));
            holder.syncItemIV.setImageResource(syncCatItem.getImageRes());
            holder.syncStatusTV.setTextColor(isChecked ? 0xff72bf44 : 0xffc43131);

            return convertView;
        }

        private void setCheckBox(ViewHolder holder, boolean isChecked) {
            holder.syncCB.setChecked(isChecked);

            if (SynchronizationManager.getInstance().isSyncAllCategoryGroupActive()) {
                holder.syncCB.setVisibility(View.GONE);
                if (isChecked) {
                    holder.progressBar.setVisibility(View.VISIBLE);
                } else {
                    holder.progressBar.setVisibility(View.GONE);
                }
            } else {
                holder.syncCB.setVisibility(View.VISIBLE);
                holder.progressBar.setVisibility(View.GONE);
            }
        }

        class DefaultOnClickListener implements OnClickListener {
            private Context context;
            private SyncPreferenceItem syncCategoryItem;
            private ViewHolder holder;

            public DefaultOnClickListener(Context context,
                                          SyncPreferenceItem syncCategoryItem,
                                          ViewHolder holder) {
                this.context = context;
                this.syncCategoryItem = syncCategoryItem;
                this.holder = holder;
            }

            @Override
            public void onClick(View view) {
                if (view.getId() == holder.syncCB.getId()) {
                    syncCategoryItem.getSyncCategory().setIsSyncEnabled(this.context, holder.syncCB.isChecked());

                    PreferencesSync.this.refreshList();
                }
            }
        }

        class ViewHolder {
            ProgressBar progressBar;
            TextView syncItemTV;
            TextView syncStatusTV;
            ImageView syncItemIV;
            CheckBox syncCB;
        }
    }

I'm using the sparseboolean array as below to get all the checkeditem position. But it always returns null.

SparseBooleanArray checkedPositions = xmlSyncItemsListView.getCheckedItemPositions();
            Log.i("sha","checkedPositions: " + checkedPositions.size());
            if (checkedPositions != null)
            {
                int count = mXmlPreferencesSyncAdpt.getCount();
                for ( int i=0;i<count;i++)
                {
                    Log.i("","Selected items: " + checkedPositions.get(i));
                }
            }

Please help me to solve the issue.