Java tutorial
/* * Copyright 2011 Google 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.google.gwt.event.dom.client; import com.google.gwt.core.client.GWT; import com.google.gwt.dom.client.DataTransfer; import com.google.gwt.dom.client.PartialSupport; import com.google.gwt.event.shared.EventHandler; /** * Base class for drag and drop events. * * @param <H> handler type */ @PartialSupport public abstract class DragDropEventBase<H extends EventHandler> extends DomEvent<H> { /** * Detector for browser support of drag events. */ static class DragSupportDetector { private final boolean isSupported = detectDragSupport(); /** * Using a run-time check, return true if drag events are supported. * * @return true if supported, false otherwise. */ public boolean isSupported() { return isSupported; } private native boolean detectDragSupport() /*-{ var elem = document.createElement('div'); elem.setAttribute('ondragstart', 'return;'); return (typeof elem.ondragstart) == "function"; }-*/; } /** * Detector for permutations that do not support drag events. */ static class DragSupportDetectorNo extends DragSupportDetector { @Override public boolean isSupported() { return false; } } /** * The implementation singleton. */ private static DragSupportDetector impl; /** * Runtime check for whether drag events are supported in this browser. * * @return true if supported, false if not */ public static boolean isSupported() { if (impl == null) { impl = GWT.create(DragSupportDetector.class); } return impl.isSupported(); } /** * Get the data for the specified format from the {@link DataTransfer} object. * * @param format the format * @return the data for the specified format */ public String getData(String format) { DataTransfer dt = getDataTransfer(); return getDataTransfer().getData(format); } /** * Get the {@link DataTransfer} associated with the current drag event. * * @return the {@link DataTransfer} object */ public DataTransfer getDataTransfer() { return getNativeEvent().getDataTransfer(); } /** * Set the data in the {@link DataTransfer} object for the specified format. * * @param format the format * @param data the data to associate with the format */ public void setData(String format, String data) { getDataTransfer().setData(format, data); } }