尝试在组件的空模型上设置模型对象：DropDownChoice

Question

我正在使用 wicket 向导让用户执行多个注册步骤。
但不知何故我得到这个错误：

Last cause: Attempt to set model object on null model of component: wizard:form:view:sprachenDrop

WicketMessage: Method onFormSubmitted of interface org.apache.wicket.markup.html.form.IFormSubmitListener targeted at [Form [Component id = form]] on component [Form [Component id = form]] threw an exception

堆栈跟踪中的这段代码：

Root cause:
java.lang.IllegalStateException: Attempt to set model object on null model of component: wizard:form:view:sprachenDrop at org.apache.wicket.Component.setDefaultModelObject(Component.java:3038) at org.apache.wicket.markup.html.form.FormComponent.setModelObject(FormComponent.java:1577) at org.apache.wicket.markup.html.form.FormComponent.updateModel(FormComponent.java:1098) at org.apache.wicket.markup.html.form.Form$FormModelUpdateVisitor.component(Form.java:230) at org.apache.wicket.markup.html.form.Form$FormModelUpdateVisitor.component(Form.java:200)

参考 this post I tried to create a class to hold the information I need, but it didn't work, I took this tutorial as basic. From Wicket's help itself I tried this code 并因此创建了一个 IClusterable class 来保存信息。错误还是一样。由于 DropDownChoice 带有一个构造函数，该构造函数能够将列表作为模型保存，因此我认为我的代码应该可以工作。

public class StepPersoenlicheDaten  extends WizardStep{
    private static final long serialVersionUID = 1L;
    private RequiredTextField<String> name, vorname, strasse, ort, telefonNr;
    private DropDownChoice<String> korrespondenzsprache;
    private List<String> sprachen = new ArrayList<String>();


    public StepPersoenlicheDaten(WizardModel model) {
        super(new ResourceModel("daten.title"), new ResourceModel("daten.summary"));
        init(model);
        java.util.Collections.addAll(sprachen, "Deutsch","English","Français","Italiano");

        add(name = new RequiredTextField<String>("name", Model.of("")));
        add(vorname = new RequiredTextField<String>("vorname",  Model.of("")));
        add(strasse = new RequiredTextField<String>("strasse",  Model.of("")));
        add(ort = new RequiredTextField<String>("ort",  Model.of("")));
        add(telefonNr = new RequiredTextField<String>("telefonNr", Model.of("")));
        add(korrespondenzsprache = new DropDownChoice<String>("sprachenDrop", sprachen));
    }
}

单击向导上的完成（或下一步）按钮时出现错误。我不知道还有什么办法可以修复它。

编辑：

IModel<Collection<? extends String>> langs = Model.of(sprachen);
add(korrespondenzsprache = new DropDownChoice<String>("sprachenDrop", langs));

未被接受。

Answer 1

创建一个本地字符串，例如 private String sprachenDrop; 并添加 getters/setters。然后添加：

add(korrespondenzsprache = new DropDownChoice<String>("sprachenDrop", 
new PropertyModel(this, "sprachenDrop"), sprachen));

应该可以。

尝试在组件的空模型上设置模型对象：DropDownChoice

Attempt to set model object on null model of component: DropDownChoice

java

wicket

dropdownchoice