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/*
 * 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.user.client.ui;

import com.google.gwt.core.client.JavaScriptObject;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.builder.shared.HtmlElementBuilder;
import com.google.gwt.dom.builder.shared.HtmlBuilderFactory;

/**
 * EXPERIMENTAL and subject to change. Do not use this in production code.
 * 

* A simple {@link Element} implementation (not an actual dom * object) that can serve as stand in to be used by {@link IsRenderable} widgets * before they are fully built. For example, it can accumulate simple set*() * values to be used when the widget is actually ready to render. Thus, most * {@link IsRenderable} widget code can be written without taking into account * whether or not the widget has yet been rendered. *

* {@link DOM#appendChild} is aware of PotentialElement, and calls its * resolve() method. This triggers a call to * {@link UIObject#resolvePotentialElement()}, which widgets can customize * to get a real {@link Element} in place at the last moment. * * TODO(rdcastro): Cover all unsupported methods with helpful error messages. */ public class PotentialElement extends Element { static { declareShim(); } public static PotentialElement as(Element e) { assert isPotential(e); return (PotentialElement) e; } /** * Builds a new PotentialElement with the tag name set to "div". * * @see #build(UIObject,String) */ public static PotentialElement build(UIObject o) { return build(o, "div"); } /** * Builds a new PotentialElement. This element keeps track of the * {@link UIObject} so that it can call * {@link UIObject#resolvePotentialElement} to get a real element when * that is needed. */ public static native PotentialElement build(UIObject o, String tagName) /*-{ var el = new $wnd.GwtPotentialElementShim(); el.tagName = tagName; el.__gwt_resolve = @com.google.gwt.user.client.ui.PotentialElement::buildResolveCallback(Lcom/google/gwt/user/client/ui/UIObject;)(o); return @com.google.gwt.dom.client.Element::as(Lcom/google/gwt/core/client/JavaScriptObject;)(el); }-*/; /** * Creates an {@link HtmlElementBuilder} instance inheriting all attributes * set for the given PotentialElement. * * @param potentialElement assumed to be a PotentialElement, used as basis for * the builder * @return a propertly configured {@link HtmlElementBuilder} instance */ public static HtmlElementBuilder createBuilderFor(Element potentialElement) { PotentialElement el = PotentialElement.as(potentialElement); HtmlElementBuilder builder = HtmlBuilderFactory.get().trustedCreate( el.getTagName()); el.mergeInto(builder); return builder; } /** * Tests whether a given {@link JavaScriptObject} represents a PotentialElement. * * @param o the {@link JavaScriptObject} to be tested * @return true if the given object is a PotentialElement instance */ public static native boolean isPotential(JavaScriptObject o) /*-{ try { return (!!o) && (!!o.__gwt_resolve); } catch (e) { return false; } }-*/; /** * If given a PotentialElement, returns the real Element to be * built from it. Otherwise returns the given Element itself. *

* Note that a PotentialElement can only be resolved once. * Making repeated calls to this method with the same PotentialElement * is an error. */ public static Element resolve(Element maybePotential) { return maybePotential.cast().resolve(); } private static native JavaScriptObject buildResolveCallback(UIObject resolver) /*-{ return function() { this.__gwt_resolve = @com.google.gwt.user.client.ui.PotentialElement::cannotResolveTwice(); return [email protected]::resolvePotentialElement()(); }; }-*/; private static final native void cannotResolveTwice() /*-{ throw "A PotentialElement cannot be resolved twice."; }-*/; private static final native void declareShim() /*-{ var shim = function() {}; shim.prototype = { className: '', clientHeight: 0, clientWidth: 0, dir: '', getAttribute: function(name, value) { return this[name]; }, href: '', id: '', lang: '', // should be @com.google.gwt.dom.client.Node.ELEMENT_MODE, but the compiler // doesn't like that. nodeType: 1, removeAttribute: function(name, value) { this[name] = undefined; }, setAttribute: function(name, value) { this[name] = value; }, src: '', style: {}, title: '' }; $wnd.GwtPotentialElementShim = shim; }-*/; protected PotentialElement() { } final native Element setResolver(UIObject resolver) /*-{ this.__gwt_resolve = @com.google.gwt.user.client.ui.PotentialElement::buildResolveCallback(Lcom/google/gwt/user/client/ui/UIObject;)(resolver); }-*/; /** * Copy only the fields that have actually changed from the values in the shim * prototype. Do this by severing the __proto__ link, allowing us to iterate * only on the fields set in this specific instance. */ private native void mergeInto(HtmlElementBuilder builder) /*-{ var savedProto = this.__proto__; var tagName = this.tagName; var gwtResolve = this.__gwt_resolve; var className = this.className; try { this.__proto__ = null; this.tagName = null; this.__gwt_resolve = null; // className needs special treatment because the actual HTML attribute is // called "class" and not "className". if (this.className) { [email protected]::className(Ljava/lang/String;)( this.className); this.className = null; } // Iterate over all attributes, and copy them to the ElementBuilder. // TODO(rdcastro): Deal with the "style" attribute. for (attr in this) { if (!this[attr]) { continue; } if (typeof this[attr] == 'number') { [email protected]::attribute(Ljava/lang/String;I)( attr, this[attr]); } else if (typeof this[attr] == 'string') { [email protected]::attribute(Ljava/lang/String;Ljava/lang/String;)( attr, this[attr]); } } } finally { this.__proto__ = savedProto; if (className) { this.className = className; } this.__gwt_resolve = gwtResolve; this.tagName = tagName; } }-*/; /** * Calls the __gwt_resolve method on the underlying * JavaScript object if it exists. On objects created via {@link #build}, this * method is a call to the {@link UIObject#resolvePotentialElement} method * on the associated UIObject. */ private native Element resolve() /*-{ return this.__gwt_resolve ? this.__gwt_resolve() : this; }-*/; }





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