org.gems.ajax.client.dnd.DragSourceManager.java Source code

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Here is the source code for org.gems.ajax.client.dnd.DragSourceManager.java

Source

package org.gems.ajax.client.dnd;

import java.util.HashMap;

import com.google.gwt.user.client.DOM;
import com.google.gwt.user.client.Element;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.EventPreview;

/*******************************************************************************
 * Copyright (c) 2007 Jules White. All rights reserved. This program and the
 * accompanying materials are made available under the terms of the Eclipse
 * Public License v1.0 which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors: Jules White - initial API and implementation
 ******************************************************************************/

public class DragSourceManager implements EventPreview {

    private static DragSourceManager instance_;

    public static DragSourceManager getInstance() {
        if (instance_ == null)
            instance_ = new DragSourceManager();

        return instance_;
    }

    private HashMap<Element, Boolean> sources_;

    public void add(DragSource ds, Element e) {
        registerDragSource(e);
    }

    public void remove(DragSource ds, Element e) {
        sources_.remove(e);
        if (sources_.size() == 0) {
            sources_ = null;
            DOM.removeEventPreview(this);
        }
    }

    private void registerDragSource(Element el) {
        if (sources_ == null) {
            sources_ = new HashMap<Element, Boolean>(37);
            DOM.addEventPreview(this);
        }
        sources_.put(el, Boolean.TRUE);
    }

    public boolean onEventPreview(Event event) {
        if (sources_ != null) {
            if (DOM.eventGetType(event) == Event.ONMOUSEDOWN) {
                Element el = DOM.eventGetTarget(event);
                if (sources_.get(el) != null)
                    DOM.eventPreventDefault(event);
            }
        }
        return true;
    }
}