TapRecognizer.java

/*
 * Copyright 2012 Daniel Kurka
 *
 * 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.googlecode.mgwt.dom.client.recognizer;

import com.google.gwt.core.client.GWT;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.Touch;
import com.google.gwt.event.dom.client.TouchCancelEvent;
import com.google.gwt.event.dom.client.TouchEndEvent;
import com.google.gwt.event.dom.client.TouchMoveEvent;
import com.google.gwt.event.dom.client.TouchStartEvent;
import com.google.gwt.event.shared.HasHandlers;

import com.googlecode.mgwt.dom.client.event.tap.TapEvent;
import com.googlecode.mgwt.dom.client.event.touch.TouchHandler;

/**
 * A recognizer that recognizes Tap events
 *
 * A Tap is the mobile equivalent of a click
 *
 * @author Daniel Kurka
 */
public class TapRecognizer implements TouchHandler {

	public static final int DEFAULT_DISTANCE = 15;

	private final int distance;

	private boolean touchCanceled;

	private boolean hasMoved;

	private int start_x;

	private int start_y;

	private Element targetElement;

	private final HasHandlers source;

	private EventPropagator eventPropagator;

	private static EventPropagator DEFAULT_EVENT_PROPAGATOR;

	public TapRecognizer(HasHandlers source) {
		this(source, DEFAULT_DISTANCE);
	}

	public TapRecognizer(HasHandlers source, int distance) {
		if (source == null)
			throw new IllegalArgumentException("source can not be null");
		if (distance < 0)
			throw new IllegalArgumentException("distance has to be greater than zero");
		this.source = source;
		this.distance = distance;
	}

	@Override
	public void onTouchStart(TouchStartEvent event) {
		touchCanceled = false;
		hasMoved = false;
		if(event.getNativeEvent() != null){
			targetElement = event.getNativeEvent().getEventTarget().<Element>cast();
		}else {
			targetElement = null;
		}

		start_x = event.getTouches().get(0).getPageX();
		start_y = event.getTouches().get(0).getPageY();
	}

	@Override
	public void onTouchMove(TouchMoveEvent event) {
		Touch touch = event.getTouches().get(0);
		if (Math.abs(touch.getPageX() - start_x) > distance || Math.abs(touch.getPageY() - start_y) > distance) {
			hasMoved = true;
		}
	}

	@Override
	public void onTouchEnd(TouchEndEvent event) {
		if (!hasMoved && !touchCanceled) {
			TapEvent tapEvent = new TapEvent(source, targetElement, start_x, start_y);
			getEventPropagator().fireEvent(source, tapEvent);
		}
	}

  @Override
  public void onTouchCancel(TouchCancelEvent event) {
    touchCanceled = true;
  }

	public int getDistance() {
		return distance;
	}

	protected EventPropagator getEventPropagator() {
		if (eventPropagator == null) {
			if (DEFAULT_EVENT_PROPAGATOR == null) {
				DEFAULT_EVENT_PROPAGATOR = GWT.create(EventPropagator.class);
			}
			eventPropagator = DEFAULT_EVENT_PROPAGATOR;
		}
		return eventPropagator;
	}

	public Element getTargetElement() {
	  return targetElement;
	}
}