CODEWITHSUNDEEP
javaajaxformswicket
fred
fred

Reputation: 1822

Wicket form ajax

This code is from the Wicket in Action book.

    final WebMarkupContainer parent = new WebMarkupContainer("comments");
    parent.setOutputMarkupId(true);
    add(parent);
    List<String> comments = ...

    parent.add(new ListView("list", comments) {

        @Override
        protected void populateItem(ListItem item) {
            item.add(new Label("comment", item.getModel()));
        }
    });

    Form form = new Form("form");
    final TextArea editor = new TextArea("editor", new Model(""));
    editor.setOutputMarkupId(true);
    form.add(editor);
    form.add(new AjaxSubmitLink("save") {
        @Override
        protected void onSubmit(AjaxRequestTarget target, Form form) {
            comments.add(editor.getModelObjectAsString());
            editor.setModel(new Model(""));
            target.addComponent(parent);
            target.focusComponent(editor);
        }
    });
    parent.add(form);

It doesn't compile. Inside the override method, the row

comments.add(editor.getModelObjectAsString());

generates the following errors in Eclipse

"Multiple markers at this line. Cannot refer to a non-final variable comments inside an inner class defined in a different method. The method getModelObjectAsString() is undefined for the type TextArea."

I love programming books written by the authors of a framework with examples that don't work =) seriously though, what is wrong here and how can it be fixed?

EDIT:

In order for it to compile in Wicket 1.4, the code needs to change to

    /* Java code */
    final WebMarkupContainer parent = new WebMarkupContainer("comments");
    parent.setOutputMarkupId(true);
    add(parent);
    final List<String> comments = new ArrayList<String>();

    parent.add(new ListView("list", comments) {

        @Override
        protected void populateItem(ListItem item) {
            item.add(new Label("comment", item.getModel()));
        }
    });

    Form form = new Form("form");
    //final TextArea editor = new TextArea("editor", new Model(""));
    final TextArea editor = new TextArea("editor", new Model(""));
    editor.setOutputMarkupId(true);
    form.add(editor);
    form.add(new AjaxSubmitLink("save") {
        @Override
        protected void onSubmit(AjaxRequestTarget target, Form form) {
            comments.add((String) editor.getModelObject());
            editor.setModel(new Model(""));
            target.addComponent(parent);
            target.focusComponent(editor);
        }
    });
    parent.add(form);

But if the list is made final, then wont it be impossible to dynamically alter its contents?

Upvotes: 1

Views: 6938

Answers (3)

Jeremy Thomerson
Jeremy Thomerson

Reputation: 742

But if the list is made final, then wont it be impossible to dynamically alter its contents?

No, a "final" variable just means that you can't reassign that variable to something else. With a collection like a List, you can manipulate its contents using add / remove, etc...

That example is simplistic however. If you are going to work with a persistent list (one from a database), you should do the following:

Rather than pass a list to your listview, pass a LoadableDetachableModel> to it. This allows it to be loaded from the database for each render and avoids memory usage and serialization problems. Then, in onSubmit, add your new Foo POJO to the database and then call detach() on the model that you passed to the list view (it will need to be "final" to reference it from within an anonymous inner class).

Upvotes: 0

bert
bert

Reputation: 7696

Putting my comment into a real answer:

The problem is the not the final on the TextArea, but that the Wicket in Action book is written for Wicket 1.3 and the APi has changed for version 1.4 / 1.5.

The migration guide for Wicket i.4 states that the members have been renamed to getDefaulModelXXX().

Have fun with wicket.

Upvotes: 2

arun
arun

Reputation: 45

remove the final key and try it i think it may work 

TextArea editor = new TextArea("editor", new Model(""));

Upvotes: 0

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