ShowMorePagerPanel.java

/*
 * Copyright 2013 ArcBees Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.gwtplatform.carstore.client.application.ui;

import com.google.gwt.user.cellview.client.AbstractPager;
import com.google.gwt.user.client.ui.ScrollPanel;
import com.google.gwt.user.client.ui.Widget;
import com.google.gwt.view.client.HasRows;

public class ShowMorePagerPanel extends AbstractPager {
    private static final int DEFAULT_INCREMENT = 20;

    private final ScrollPanel scrollable = new ScrollPanel();

    private int incrementSize = DEFAULT_INCREMENT;
    private int lastScrollPos;

    public ShowMorePagerPanel(int pageSize) {
        incrementSize = pageSize;
        initWidget(scrollable);

        // Do not let the scrollable take tab focus.
        scrollable.getElement().setTabIndex(-1);

        // Handle scroll events.
        scrollable.addScrollHandler(event -> {
            // If scrolling up, ignore the event.
            int oldScrollPos = lastScrollPos;
            lastScrollPos = scrollable.getVerticalScrollPosition();
            if (oldScrollPos >= lastScrollPos) {
                return;
            }

            HasRows display1 = getDisplay();
            if (display1 == null) {
                return;
            }

            int maxScrollTop = scrollable.getWidget().getOffsetHeight()
                    - scrollable.getOffsetHeight();
            if (lastScrollPos >= maxScrollTop - 16) {
                // We are near the end, so increase the page size.
                int newPageSize = Math.min(display1.getVisibleRange()
                        .getLength() + incrementSize, display1.getRowCount());
                display1.setVisibleRange(0, newPageSize);
            }
        });
    }

    public int getIncrementSize() {
        return incrementSize;
    }

    public void setIncrementSize(int incrementSize) {
        this.incrementSize = incrementSize;
    }

    @Override
    public void setDisplay(HasRows display) {
        assert display instanceof Widget : "display must extend Widget";
        scrollable.setWidget((Widget) display);
        super.setDisplay(display);
    }

    @Override
    protected void onRangeOrRowCountChanged() {
    }
}