在Apache wicket中使用Ajax显示面板
[英]Displaying panel using ajax in apache wicket
问题描述
I am learning wicket framework and while working with ajax I tried one example in which I want to display a panel with selected radio button's company name. 
我正在学习wicket框架，并且在使用ajax时尝试了一个示例，该示例中要显示一个面板，其中包含选定的单选按钮的公司名称。 But while doing this I am getting some error. 但是在执行此操作时，出现了一些错误。 Here I mentioned all details from my coding: 在这里，我提到了编码中的所有细节：
Test.java Test.java
public class Test extends WebPage {
private static final List<String> companies = Arrays.asList(new String[] {"Google","Microsoft","Yahoo"});
private ArrayList<String> compSelected = new ArrayList<String>();
private Panel panel;
public Test(final PageParameters parameters) {
final RadioChoice<String> companyList =
new RadioChoice<String>("companyNames",new Model(compSelected),companies);
companyList.add(new AjaxFormChoiceComponentUpdatingBehavior() {
@Override
protected void onUpdate(AjaxRequestTarget target) {
if("Google".equals(companyList.getModelObject())){
panel = new Panel1("panel1","Google");
}
else if("Microsoft".equals(companyList.getModelObject())){
panel = new Panel1("panel1","Microsoft");
}
else{
panel = new Panel1("panel1","Yahoo");
}
panel.setOutputMarkupId(true);
target.addComponent(panel);
}});
Form<?> form = new Form<Void>("form");
add(form);
form.add(companyList);
form.add(panel);
this.add(form);
}
}
Test.html 的test.html
<form wicket:id="form">
<label><b>Company List:</b></label><br>
<span wicket:id="companyNames">radio button list will goes here</span><br>
<span wicket:id = "panel1" class="panel">panel goes here</span>
</form>
Panel1.java Panel1.java
@SuppressWarnings("serial")
public class Panel1 extends Panel{
public Panel1(String id,String cName) {
super(id);
add(new Label("msg", "selected company is:"+ cName));
}
}
Panel1.html Panel1.html
<body>
<wicket:panel>
<span wicket:id="msg">message goes here</span>
</wicket:panel>
</body>
WicketMessage: Can't instantiate page using constructor public demo.wicket.ajax.Test(org.apache.wicket.PageParameters) and argument Root cause:java.lang.IllegalArgumentException: argument child may not be null at org.apache.wicket.MarkupContainer.add(MarkupContainer.java:131) at demo.wicket.ajax.Test.(Test.java:46) at java.lang.reflect.Constructor.newInstance(Unknown Source) at org.apache.wicket.session.DefaultPageFactory.createPage(DefaultPageFactory.java:188) at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:65) at org.apache.wicket.request.target.component.BookmarkablePageRequestTarget.newPage(BookmarkablePageRequestTarget.java:299) at org.apache.wicket.request.target.component.BookmarkablePageRequestTarget.getPage(BookmarkablePageRequestTarget.java:321) at org.apache.wicket.request.target.component.BookmarkablePageRequestTarget.processEvents(BookmarkablePageRequestTarget.java:234) at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents
I am not sure what I did wrong here. 我不确定我在这里做错了什么。 can someone please help me to figure it out? 有人可以帮我弄清楚吗？
1 个解决方案
解决方案1
0 2015-07-16 06:38:53
The problem is form.add(panel); 问题是form.add(panel); . 。 panel is null at that time. panel当时为null。 You initialize it in #onUpdate() but it is executed only after a click(?) on the radio buttons. 您可以在#onUpdate()中#onUpdate()初始化，但只有在单选按钮上单击（？）后才能执行。
Solution: 解：
Change panel type to WebMarkupContainer and initialize it in the page's constructor. 将panel类型更改为WebMarkupContainer ，然后在页面的构造函数中对其进行初始化。 Call panel.setOutputMarkupId(true) also in the constructor so the <span wicket:id="panel1"...> has an id in the rendered HTML and being able to be referenced later with JS to replace/update it. 在构造函数中也调用panel.setOutputMarkupId(true) ，以便<span wicket:id="panel1"...>在呈现的HTML中具有一个id ，并且以后可以用JS引用以替换/更新它。 In #onUpdate() use something like panel = panel.replaceWith(new Panel1(panel.getId(), choice.getModelObject())); target.add(panel); 在#onUpdate()使用诸如panel = panel.replaceWith(new Panel1(panel.getId(), choice.getModelObject())); target.add(panel); panel = panel.replaceWith(new Panel1(panel.getId(), choice.getModelObject())); target.add(panel);
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