PulldownListViewHelper

import android.util.Log;
import android.widget.AbsListView;
import android.widget.ListView;
import org.jetbrains.annotations.NotNull;

/**
 * Makes a listview to have a pull down, this is a wrapper.
 * Is not a good idea to override a ListView because there
 * are a lot of libraries and we dont know when we need one.
 */
public class PulldownListViewHelper {

    private final static int ITEMS_BEFORE_LAST_TO_DETECT = 3;

    /**
     * ListView to play with
     */
    private ListView listView;

    /**
     * OnPullDownListener
     */
    private OnPullDownListener listener;

    /**
     * Listener of scroll view that makes the list to attend to pull down events
     */
    AbsListView.OnScrollListener scrolllistener = new AbsListView.OnScrollListener() {

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) { }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {

            Log.d("PulldownListViewHelper", "FVI: " + firstVisibleItem + ", VIC:" +visibleItemCount+ ", TIC:" + totalItemCount);
            final int lastItem = firstVisibleItem + visibleItemCount;
            if(listener != null && lastItem >= (totalItemCount - ITEMS_BEFORE_LAST_TO_DETECT)) {
                listener.onPullDown();
            }

        }

    };

    /**
     * Default constructor
     * @param listView the listview to check pulldowns
     * @param listener the listener to attend pulldown events
     */
    public PulldownListViewHelper(@NotNull ListView listView, @NotNull OnPullDownListener listener) {
        this.listView = listView;
        this.listener = listener;
    }

    /**
     * Inits pull down listening
     */
    public void initPulldown() {
        listView.setOnScrollListener(scrolllistener);
    }

    /**
     * Stops pull down listening
     */
    public void stopPulldown() {
        listView.setOnScrollListener(null);
    }

    /**
     * Simple interface for notify pull down events
     */
    public interface OnPullDownListener {

        /**
         * Method to notify pull down events
         */
        void onPullDown();

    }

}