DirectionScrollListener.java

/**
 * Odoo, Open Source Management Solution
 * Copyright (C) 2012-today Odoo SA (<http:www.odoo.com>)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http:www.gnu.org/licenses/>
 *
 * Created on 9/1/15 2:24 PM
 */
package odoo.controls.fab;

import android.view.View;
import android.widget.AbsListView;

public class DirectionScrollListener implements AbsListView.OnScrollListener {
    public static final String TAG = DirectionScrollListener.class.getSimpleName();
    private static final int DIRECTION_CHANGE_THRESHOLD = 1;
    private final FloatingActionButton mFloatingActionButton;
    private int mPrevPosition;
    private int mPrevTop;
    private boolean mUpdated;

    DirectionScrollListener(FloatingActionButton floatingActionButton) {
        mFloatingActionButton = floatingActionButton;
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
                         int visibleItemCount, int totalItemCount) {
        final View topChild = view.getChildAt(0);
        int firstViewTop = 0;
        if (topChild != null) {
            firstViewTop = topChild.getTop();
        }
        boolean goingDown;
        boolean changed = true;
        if (mPrevPosition == firstVisibleItem) {
            final int topDelta = mPrevTop - firstViewTop;
            goingDown = firstViewTop < mPrevTop;
            changed = Math.abs(topDelta) > DIRECTION_CHANGE_THRESHOLD;
        } else {
            goingDown = firstVisibleItem > mPrevPosition;
        }
        if (changed && mUpdated) {
            mFloatingActionButton.hide(goingDown);
        }
        mPrevPosition = firstVisibleItem;
        mPrevTop = firstViewTop;
        mUpdated = true;
    }

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