Question

Assume following component tree:

• A
  • B
  • C

A has a private field (called filter) and the reference to the filter is passed on to B and C.
In class B a property of the filter is modified through an AjaxLink (so no page refresh).
I see (through) logging that after each ajax call wicket will serialize A, B and C.

Now, everything works fine, clicking in the AjaxLinks in B will nicely update the filter and will refresh C and show the correct information in C (based on the filter).

However, assume if click an AjaxLink in B which will update a property of the filter to (for instance) value 2. Afterwards I press F5, it still works and the page (and all components in it) is deserialized (and again serialized afterwards). I then click on an AjaxLink the changes the value of the mentioned property to 3; this still works fine. If, however, I then do a page refresh (F5) the value of that property suddenly becomes 2 again.

It seems that on the page refresh (when wicket will load the page from disk) wicket is deserializing an older version of the filter.

Schematically:

1. Page initial load:
   => filter.value = 3 -> serialized
2. AjaxLink:
   => filter.value = 2 -> serialized
3. Page refresh:
   => filter.value = 2 -> deserialized/serialized
4. AjaxLink:
   => filter.value = 3 -> serialized
5. Page refresh:
   => filter.value = 2 -> deserialized/serialized

It seems that on action 5 the serialized version after action 4 is ignored and the serialized version after action 3 the loaded.

Hoping for a cause, explanation and if possible also the solution 🙂

CODE

public class A extends Panel { //creates the filter and passes the reference on 
        Filter filter = new Filter(TypeEnum.ALL);

    public A(final String id) {
        super(id);

    add(new B("filterPanel", filter));
    add(new C("datatable", filter));
}



    public class B extends Panel { //updates the filter

        Filter filter;;
        public B(final String id, Filter filter) {
            super(id);
            this.filter = filter;
            add(new IndicatingAjaxLink<Void>("other") {

            @Override
            public void onClick(AjaxRequestTarget target) {
                filter.setType(TypeEnum.OTHER);
                            ...
            }
        };
        }

    }

public class C extends Panel { //uses the filter

    Filter filter;;
    public C(final String id, Filter filter) {
            super(id);
            this.filter = filter;
    }

    public void populateRepeatingView() {
         final List<? extends WallEntry> result = service.find(filter);
         ...
    }    
}

Code has been simplified and I retained only the (I assume) pertinent stuff.

UPDATE

If I add following in my page class then it works:

@Override
public boolean isVersioned() {
    return false;
}

Not sure however about the implications of this and why this makes it work. Isn’t the page (de)serialized anymore?

UPDATE

I added following to my Page class:

private void writeObject(ObjectOutputStream oos) throws IOException { 
oos.defaultWriteObject(); 
System.err.println("Writing " + this + something to print out the type of the filter); 
} 

private void readObject(ObjectInputStream ois) throws ClassNotFoundException, IOException { 
ois.defaultReadObject(); 
System.err.println("Reading " + this + something to print out the type of the filter); 
} 

1. When the Page is loaded first it prints (actually it prints this 5 times, not sure if it’s normal):
   Writing [Page class = com.bnpp.ecom.homepage.web.Homepage, id = 0, render count = 1]: type = ALL

2. When I click on AjaxLink ‘ALL’ (that will update the filter) it still prints:
   Writing [Page class = com.bnpp.ecom.homepage.web.Homepage, id = 0, render count = 1]: type = ALL

3. When I click on AjaxLink ‘DISCUSSIONS’ (that will update the filter) it still prints:
   Writing [Page class = com.bnpp.ecom.homepage.web.Homepage, id = 0, render count = 1]: type = DISCUSSIONS

4. When I refresh the page (F5) the pageid is updated:
   Writing [Page class = com.bnpp.ecom.homepage.web.Homepage, id = 1, render count = 2]: type = DISCUSSIONS

5. When I click on AjaxLink ‘ALL’ (that will update the filter) it prints:
   Writing [Page class = com.bnpp.ecom.homepage.web.Homepage, id = 1, render count = 1]: type = ALL

6. So far so good but when I refresh the page now (F5) this is printed out:
   Reading [Page class = com.bnpp.ecom.homepage.web.Homepage, id = 0, render count = 1]: type = DISCUSSIONS
   Writing [Page class = com.bnpp.ecom.homepage.web.Homepage, id = 2, render count = 2]: type = DISCUSSIONS

The url never changes, it stays http://…/?0

So it deserializes the page with id 0 although the last known page id was 1 and all changes that were done for version 1 are ignored (in this case switching the type from DISCUSSIONS to ALL).

Created a issue in the wicket jira for this: https://issues.apache.org/jira/browse/WICKET-4360

Answer 1

As mentioned in the jira issue: https://issues.apache.org/jira/browse/WICKET-4360 you need to setreuseitems on listviews to true or an ajax call will dirty your page when the listview is repopulated:

On F5 Wicket reads (once) the current page. But then it writes a the
page with a new page id because of the usage of ListView
(PropertyListView in DataPanel). By adding
“commentsListView.setReuseItems(true);” all is fine. See WICKET-4286
for a discussion about the ListView problem.