| /* |
| * Copyright 2008 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; |
| |
| /** |
| * Convenience class to help lazy loading. The bulk of a LazyPanel is not |
| * instantiated until {@link #setVisible}(true) or {@link #ensureWidget} is |
| * called. |
| * <p> |
| * <h3>Example</h3> {@example com.google.gwt.examples.LazyPanelExample} |
| */ |
| public abstract class LazyPanel extends SimplePanel { |
| |
| public LazyPanel() { |
| } |
| |
| /** |
| * Create the widget contained within the {@link LazyPanel}. |
| * |
| * @return the lazy widget |
| */ |
| protected abstract Widget createWidget(); |
| |
| /** |
| * Ensures that the widget has been created by calling {@link #createWidget} |
| * if {@link #getWidget} returns <code>null</code>. Typically it is not |
| * necessary to call this directly, as it is called as a side effect of a |
| * <code>setVisible(true)</code> call. |
| */ |
| public void ensureWidget() { |
| Widget widget = getWidget(); |
| if (widget == null) { |
| widget = createWidget(); |
| setWidget(widget); |
| } |
| } |
| |
| @Override |
| /* |
| * Sets whether this object is visible. If <code>visible</code> is |
| * <code>true</code>, creates the sole child widget if necessary by calling |
| * {@link #ensureWidget}. |
| * |
| * @param visible <code>true</code> to show the object, <code>false</code> to |
| * hide it |
| */ |
| public void setVisible(boolean visible) { |
| if (visible) { |
| ensureWidget(); |
| } |
| super.setVisible(visible); |
| } |
| } |