Java tutorial
/* * Copyright 2000-2016 Vaadin Ltd. * * 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.vaadin.client.extensions; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import com.google.gwt.core.client.JsArrayString; import com.google.gwt.dom.client.BrowserEvents; import com.google.gwt.dom.client.DataTransfer; import com.google.gwt.dom.client.Element; import com.google.gwt.dom.client.NativeEvent; import com.google.gwt.user.client.ui.Widget; import com.vaadin.client.ComponentConnector; import com.vaadin.client.ServerConnector; import com.vaadin.event.dnd.DropTargetExtension; import com.vaadin.shared.ui.Connect; import com.vaadin.shared.ui.dnd.DropTargetRpc; import com.vaadin.shared.ui.dnd.DropTargetState; import elemental.events.Event; import elemental.events.EventListener; import elemental.events.EventTarget; /** * Extension to add drop target functionality to a widget for using HTML5 drag * and drop. Client side counterpart of {@link DropTargetExtension}. */ @Connect(DropTargetExtension.class) public class DropTargetExtensionConnector extends AbstractExtensionConnector { private static final String CLASS_DRAG_OVER = "v-drag-over"; // Create event listeners private final EventListener dragEnterListener = this::onDragEnter; private final EventListener dragOverListener = this::onDragOver; private final EventListener dragLeaveListener = this::onDragLeave; private final EventListener dropListener = this::onDrop; /** * Widget of the drop target component. */ private Widget dropTargetWidget; @Override protected void extend(ServerConnector target) { dropTargetWidget = ((ComponentConnector) target).getWidget(); EventTarget dropTarget = getDropTargetElement().cast(); // dragenter event dropTarget.addEventListener(BrowserEvents.DRAGENTER, dragEnterListener); // dragover event dropTarget.addEventListener(BrowserEvents.DRAGOVER, dragOverListener); // dragleave event dropTarget.addEventListener(BrowserEvents.DRAGLEAVE, dragLeaveListener); // drop event dropTarget.addEventListener(BrowserEvents.DROP, dropListener); } @Override public void onUnregister() { super.onUnregister(); EventTarget dropTarget = getDropTargetElement().cast(); // Remove listeners dropTarget.removeEventListener(BrowserEvents.DRAGENTER, dragEnterListener); dropTarget.removeEventListener(BrowserEvents.DRAGOVER, dragOverListener); dropTarget.removeEventListener(BrowserEvents.DRAGLEAVE, dragLeaveListener); dropTarget.removeEventListener(BrowserEvents.DROP, dropListener); } /** * Finds the drop target element within the widget. By default, returns the * topmost element. * * @return the drop target element in the parent widget. */ protected Element getDropTargetElement() { return dropTargetWidget.getElement(); } /** * Event handler for the {@code dragenter} event. * * @param event * browser event to be handled */ protected void onDragEnter(Event event) { addTargetIndicator(getDropTargetElement()); } /** * Event handler for the {@code dragover} event. * * @param event * browser event to be handled */ protected void onDragOver(Event event) { NativeEvent nativeEvent = (NativeEvent) event; if (isDragOverAllowed(nativeEvent)) { // Set dropEffect parameter if (getState().dropEffect != null) { nativeEvent.getDataTransfer() .setDropEffect(DataTransfer.DropEffect.valueOf(getState().dropEffect.name())); } // Prevent default to allow drop nativeEvent.preventDefault(); nativeEvent.stopPropagation(); } else { // Remove drop effect nativeEvent.getDataTransfer().setDropEffect(DataTransfer.DropEffect.NONE); // Remove drop target indicator removeTargetIndicator(getDropTargetElement()); } } /** * Determines if dragover event is allowed on this drop target according to * the dragover criteria. * * @param event * Native dragover event. * @return {@code true} if dragover is allowed, {@code false} otherwise. * @see DropTargetExtension#setDragOverCriteria(String) */ protected boolean isDragOverAllowed(NativeEvent event) { if (getState().dragOverCriteria != null) { return executeScript(event, getState().dragOverCriteria); } // Allow when criteria not set return true; } /** * Event handler for the {@code dragleave} event. * * @param event * browser event to be handled */ protected void onDragLeave(Event event) { removeTargetIndicator(getDropTargetElement()); } /** * Event handler for the {@code drop} event. * * @param event * browser event to be handled */ protected void onDrop(Event event) { NativeEvent nativeEvent = (NativeEvent) event; if (dropAllowed(nativeEvent)) { nativeEvent.preventDefault(); nativeEvent.stopPropagation(); // Initiate firing server side drop event JsArrayString typesJsArray = getTypes(nativeEvent.getDataTransfer()); List<String> types = new ArrayList<>(); Map<String, String> data = new HashMap<>(); for (int i = 0; i < typesJsArray.length(); i++) { types.add(typesJsArray.get(i)); data.put(typesJsArray.get(i), nativeEvent.getDataTransfer().getData(typesJsArray.get(i))); } getRpcProxy(DropTargetRpc.class).drop(types, data, getState().dropEffect, data.get(DragSourceExtensionConnector.DATA_TYPE_DRAG_SOURCE_ID)); } removeTargetIndicator(getDropTargetElement()); } private boolean dropAllowed(NativeEvent event) { if (getState().dropCriteria != null) { return executeScript(event, getState().dropCriteria); } // Allow when criteria not set return true; } private void addTargetIndicator(Element element) { element.addClassName(CLASS_DRAG_OVER); } private void removeTargetIndicator(Element element) { element.removeClassName(CLASS_DRAG_OVER); } private native boolean executeScript(NativeEvent event, String script)/*-{ return new Function('event', script)(event); }-*/; private native JsArrayString getTypes(DataTransfer dataTransfer)/*-{ return dataTransfer.types; }-*/; @Override public DropTargetState getState() { return (DropTargetState) super.getState(); } }