GWT懒加载

Question

GWT是否有LazyPanel。我无法看到它。请让我知道。如果它得到lazyPanel，请让我再知道版本

Answer 1

我同意rustyshelf在谷歌搜索的原理，但由于StackOverflow的是这也是一个参考本身，这里有一个更详细的答案：

默认情况下，不显示LazyPanel。只有在LazyPanel上调用setVisible（true）时才会创建底层窗口小部件。

当子面板包含相对较重的内容时，该类主要应与StackPanel，DisclosurePanel和TabPanel一起使用。
使用​​来包装这些内容的创建可以显着提高用户体验。

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Using the LazyPanel is simple。所有你需要做的就是添加你想懒惰地加载到懒惰面板的小部件，然后在懒惰面板上调用setVisible（true）以实际上按需加载小部件。值得一提的是，LazyPanel主要用于像TabPanel和StackPanel这样的小部件，在所有情况下都不是很理想。

Answer 2

这是来自“候选版本”GWT的LazyPanel.java 1.6.2 所以是的，简单的，以及上述答案的确认。

/* 
* 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); 
    } 
}