AbsListViewScrollDetector.java

/*
 * Copyright (C) 2015 Federico Iosue (federico.iosue@gmail.com)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package it.feio.android.omninotes.models.listeners;

import android.support.annotation.NonNull;
import android.view.View;
import android.widget.AbsListView;


public abstract class AbsListViewScrollDetector implements AbsListView.OnScrollListener {

    private int mLastScrollY;
    private int mPreviousFirstVisibleItem;
    private AbsListView mListView;
    private int mScrollThreshold;


    public abstract void onScrollUp();

    public abstract void onScrollDown();


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


    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        if (isSameRow(firstVisibleItem)) {
            int newScrollY = getTopItemScrollY();
            boolean isSignificantDelta = Math.abs(mLastScrollY - newScrollY) > mScrollThreshold;
            if (isSignificantDelta) {
                if (mLastScrollY > newScrollY) {
                    onScrollUp();
                } else {
                    onScrollDown();
                }
            }
            mLastScrollY = newScrollY;
        } else {
            if (firstVisibleItem > mPreviousFirstVisibleItem) {
                onScrollUp();
            } else {
                onScrollDown();
            }

            mLastScrollY = getTopItemScrollY();
            mPreviousFirstVisibleItem = firstVisibleItem;
        }
    }


    public void setScrollThreshold(int scrollThreshold) {
        mScrollThreshold = scrollThreshold;
    }


    public void setListView(@NonNull AbsListView listView) {
        mListView = listView;
    }


    private boolean isSameRow(int firstVisibleItem) {
        return firstVisibleItem == mPreviousFirstVisibleItem;
    }


    private int getTopItemScrollY() {
        if (mListView == null || mListView.getChildAt(0) == null) {
            return 0;
        }
        View topChild = mListView.getChildAt(0);
        return topChild.getTop();
    }
}