java - DropDownChoices 返回 null 作为下拉列表中所选项目的值

Question

我正在尝试访问用户在 apache wicket 的 DropDownChoices 中选择的值。我将 AjaxFormComponentUpdatingBehavior 添加到 DropDownChoices 元素。我在 onUpdate 行为方法中将 null 作为选定选项。我尝试通过不同方式访问选定的值，如以下代码所示，但在调试时仍然为空。

私有(private)字符串selectedMake;

private final Map<String, List<String>> modelsMap = new HashMap<String, List<String>>(); // map:company->model

    modelsMap.put( "AUDI", Arrays.asList( "A4", "A6", "TT" ) );
    modelsMap.put( "CADILLAC", Arrays.asList( "CTS", "DTS", "ESCALADE", "SRX", "DEVILLE" ) );
    modelsMap.put( "FORD", Arrays.asList( "CROWN", "ESCAPE", "EXPEDITION", "EXPLORER", "F-150" ) );

    IModel<List<? extends String>> makeChoices = new AbstractReadOnlyModel<List<? extends String>>() {
        @Override
        public List<String> getObject() {
            return new ArrayList<String>( modelsMap.keySet() );
        }

    };

    lastDropDownChoice = new DropDownChoice<String>( "daynamicTimeConstrains",
                                                     new PropertyModel<String>( this, "selectedMake" ), makeChoices );

    lastDropDownChoice.add( new AjaxFormComponentUpdatingBehavior( "onchange" ) {
        @Override
        protected void onUpdate( AjaxRequestTarget target ) {

            // Getting this as null 
            System.out.println( selectedMake );

            // Getting this as null
            getFormComponent().getModel().getObject();

        }
    } );

Answer 1

使用OnChangeAjaxBehavior 。这段代码对我有用:

public class HomePage extends WebPage {

    private String text;

    public String getText() {
        return text;
    }

    private static final List l = Arrays.asList("a", "b", "c");

    public HomePage(final PageParameters parameters) {
        super(parameters);
        add(ddc());
    }

    private DropDownChoice ddc(){
        DropDownChoice ddc = new DropDownChoice("ddc", new PropertyModel(this, "text"), l);
        ddc.add(new OnChangeAjaxBehavior() {

            @Override
            protected void onUpdate(AjaxRequestTarget target) {
                System.out.println(getComponent().getDefaultModelObjectAsString());
                System.out.println("getText: " + getText());
            }
        });
        return ddc;
    }

}