2

我已经开始学习 Apache Wicket Web 框架，但我在完成一项任务时遇到了一些困难。

如果您可以从附图中看到，我去了http://www.wicket-library.com/wicket-examples-6.0.x/echo/，

试用这个基本的输入表单功能。

我的问题是：我最初不想在标签字段中显示任何内容，但是一旦单击了设置消息按钮，我就想更新标签值。我怎么做 ？谢谢

在此处输入图像描述

更新 ：

echo.java 中的代码如下所示。PropertyModel 附有更新值的标签。

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.wicket.examples.echo;

import org.apache.wicket.examples.WicketExamplePage;
import org.apache.wicket.markup.html.basic.Label;
import org.apache.wicket.markup.html.form.Form;
import org.apache.wicket.markup.html.form.TextField;
import org.apache.wicket.model.PropertyModel;


/**
 * The simplest form application possible. Just prints any user input to a label.
 * 
 * @author Eelco Hillenius
 */
public class Echo extends WicketExamplePage
{
    private String message = "[type your message to the world here]";

    /**
     * Constructor.
     */
    public Echo()
    {
        // This model references the page's message property and is
        // shared by the label and form component
        PropertyModel<String> messageModel = new PropertyModel<String>(this, "message");

        // The label displays the currently set message
        add(new Label("msg", messageModel));

        // Add a form to change the message. We don't need to do anything
        // else with this form as the shared model is automatically updated
        // on form submits
        Form<?> form = new Form("form");
        form.add(new TextField<String>("msgInput", messageModel));
        add(form);
    }

    /**
     * @return the message
     */
    public String getMessage()
    {
        return message;
    }

    /**
     * @param message
     *            the message to set
     */
    public void setMessage(String message)
    {
        this.message = message;
    }
}

html 文件如下所示：

<?xml version="1.0" encoding="UTF-8"?>
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:wicket="http://wicket.apache.org">
<head>
    <title>Wicket Examples - echo</title>
    <link rel="stylesheet" type="text/css" href="style.css"/>
</head>
<body>
    <span wicket:id="mainNavigation"/>

    <form wicket:id="form">
        <input type="text" wicket:id="msgInput" value="" size="50" />
        <input type="submit" value="set message" />
    </form>
    <span wicket:id="msg" id="msg">Message goes here</span>

</body>
</html>
4

1 回答 1

3

尝试这个：

add(new Label("msg", messageModel)) {
  @Override public boolean isVisible() {
    return !messageModel.getObject().equals(message);
  }
};

文本字段需要知道何时应该呈现。请注意，如果您想通过 Ajax 使组件可见，则需要设置setOutputMarkupId(true)和setOutputMarkupPlaceholderTag(true)on ，例如，该组件是一个.LabelsubmitAjaxSubmitButton

当执行比String比较更复杂的任务时，您应该setVisible从覆盖的onConfigure方法中调用，如评论中所述。isVisible在渲染阶段可能会被调用很多次，这样您就想避免计算。这将如下所示：

add(new Label("msg", messageModel)) {
  @Override protected void onConfigure() {
    super.onConfigure();
    setVisible(!messageModel.getObject().equals(message));
  }
};

但是，永远不要忘记调用该super方法。

为了提高代码的可读性，我个人更喜欢重写该isVisible方法来完成String您需要的比较等简单任务。JIT 编译器通常会负责其余的工作。

于 2014-02-02T13:18:53.243 回答