ScrollPanel.java

/*
 * Copyright (c) 2010 Zhihua (Dennis) Jiang
 * 
 * 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.gwtmobile.ui.client.widgets;

import com.google.gwt.dom.client.Style;
import com.google.gwt.dom.client.Style.Unit;
import com.google.gwt.user.client.Element;
import com.google.gwt.user.client.ui.HasWidgets;
import com.google.gwt.user.client.ui.Widget;
import com.gwtmobile.ui.client.event.DragController;
import com.gwtmobile.ui.client.event.DragEvent;
import com.gwtmobile.ui.client.event.DragEventsHandler;
import com.gwtmobile.ui.client.event.SwipeEvent;
import com.gwtmobile.ui.client.event.SwipeEventsHandler;
import com.gwtmobile.ui.client.utils.Utils;

public class ScrollPanel extends PanelBase 
implements HasWidgets, DragEventsHandler, SwipeEventsHandler {

	private boolean _hasTextBox = false;
	
    public ScrollPanel() {
        setStyleName("ScrollPanel");
    }
    
    public void setHasTextBox(boolean hasTextBox) {    	
		_hasTextBox = hasTextBox && Utils.isAndroid();
	}

	public boolean getHasTextBox() {
		return _hasTextBox;
	}

    @Override
	public void onLoad() {
        DragController.get().addDragEventsHandler(this);
        DragController.get().addSwipeEventsHandler(this);
	}
	
	@Override
	public void onUnload() {
        DragController.get().removeDragEventsHandler(this);
        DragController.get().removeSwipeEventHandler(this);
	}
	
	@Override
    public Widget getWidget() {
    	return _panel.getWidget(0);
    }
    
	public void reset() {
        Utils.setTransitionDuration(getWidget().getElement(), 0);
        Utils.setTranslateY(getWidget().getElement(), 0);
	}
	
	public void setPostionToTop() {
        Utils.setTransitionDuration(getWidget().getElement(), 0);
	    Utils.setTranslateY(getWidget().getElement(), 0);
	}
	
	public void setPositionToBottom() {
        Utils.setTransitionDuration(getWidget().getElement(), 0);
        Utils.setTranslateY(getWidget().getElement(), 
                this.getElement().getClientHeight() - this.getElement().getScrollHeight());
	}
	
	public void setScrollPosition(int pos) {
		if (_hasTextBox) {
			setStyleTop(pos);
		}
		else {
			Element element = getWidget().getElement();
			Utils.setTranslateY(element, pos);
		}
	}
	
	public int getScrollPosition() {
		if (_hasTextBox) {
			return getStyleTop();
		}
		else {
			Element element = getWidget().getElement();
			return Utils.getTranslateY(element);
		}
	}
	
	public int getScrollToPosition() {
		if (_hasTextBox) {
			return getStyleTop();
		}
		else {
			Element element = getWidget().getElement();
			return Utils.getMatrixY(element);
		}
	}
	
	@Override
    public void onDragStart(DragEvent e) {
		int matrix = getScrollToPosition();
		int current = getScrollPosition();
		Utils.setTransitionDuration(getWidget().getElement(), 0);
		if (current != matrix) {  //scroll on going
			int diff = current - matrix;
			int offset = diff > 2 ? 2 : diff > -2 ? diff : -2;
			setScrollPosition(matrix + offset);
			DragController.get().suppressNextClick();
		}
	}

	@Override
    public void onDragMove(DragEvent e) {
		Element widgetEle = getWidget().getElement();
		int panelHeight = Utils.getHeight(this.getElement());
		int widgetHeight = widgetEle.getOffsetHeight();
		int current = getScrollPosition();
		if (current > 0) {//exceed top boundary
			if (e.OffsetY > 0) { 	//resist scroll down.
				current += (int)(e.OffsetY / 2);	// need the cast for production mode.
			}
			else {				
				current += e.OffsetY * 2;				
			}
		}
		else if (-current + panelHeight > widgetHeight) { //exceed bottom boundary
			if (e.OffsetY < 0) { 	//resist scroll up.
				current += (int)(e.OffsetY / 2);
			}
			else {				
				current += e.OffsetY * 2;				
			}
		}
		else {
			current += e.OffsetY;
		}
		setScrollPosition(current);		
	}

	@Override
    public void onDragEnd(DragEvent e) {
		Element widgetEle = getWidget().getElement();
		int current = getScrollPosition();
		if (current == 0) {
			return;
		}
		int panelHeight = Utils.getHeight(this.getElement());
		int widgetHeight = widgetEle.getOffsetHeight();
		if (current > 0 //exceed top boundary
				|| panelHeight > widgetHeight) {
			Utils.setTransitionDuration(widgetEle, 500);
			setScrollPosition(0);
		}
		else if (-current + panelHeight > widgetHeight) { //exceed bottom boundary
			Utils.setTransitionDuration(widgetEle, 500);
			setScrollPosition(panelHeight - widgetHeight);
		}
	}

	@Override
    public void onSwipeVertical(SwipeEvent e) {
		Element widgetEle = getWidget().getElement();
		int panelHeight = Utils.getHeight(this.getElement());
		int widgetHeight = widgetEle.getOffsetHeight();
		long current = getScrollPosition();
		if ((current >= 0) // exceed top boundary
			|| (-current + panelHeight >= widgetHeight)) { // exceed bottom boundary
			return;
		}
		
		double speed = e.getSpeed();		
		double timeFactor = 3000;
		long time =  (long) Math.abs(speed * timeFactor);
		double dicstanceFactor = 0.25;
		long distance = (long) (speed * time * dicstanceFactor);
		//Utils.Console("speed " + speed + " time " + time + " distance " + distance + " current " + current);
		current += distance;
		if (current > 0) {//exceed top boundary
			double timeAdj = 1 - (double)current / distance;
			time = (long) (time * timeAdj);
			current = 0;
		}
		else if (-current + panelHeight > widgetHeight) { //exceed bottom boundary
			long bottom = panelHeight - widgetHeight;
			double timeAdj = 1 - (double)(current - bottom) / distance;
			time = (long) (time * timeAdj);
			current = bottom;
		}
		Utils.setTransitionDuration(widgetEle, time);
		setScrollPosition((int) current);
	}

    @Override
    public void onSwipeHorizontal(SwipeEvent e) {
    }

	@Override
	public void add(Widget w) {
		assert _panel.getWidgetCount()  == 0 : "Can only add one widget to ScrollPanel.";
		super.add(w);
		if (Utils.isIOS()) {
			Utils.setTranslateY(w.getElement(), 0); //anti-flickering on iOS.
		}
	}
	
	private int getStyleTop() {
		Style style = getWidget().getElement().getStyle();
		String top = style.getTop();
		if (top.isEmpty()) {
			return 0;
		}
		else {
			return Integer.parseInt(top.replace("px", ""));
		}
	}

	private void setStyleTop(int top) {
		Style style = getWidget().getElement().getStyle();
		style.setTop(top, Unit.PX);
	}
	
}