ZK Developer's Reference/MVC/Controller/Wire Variables

Wire Variables

SelectorComposer not only wires UI components, but also wires beans from implicit objects and registered variable resolvers.

 

Wire from Implicit Objects

Wiring from implicit object is equivalent to calling Components.getImplicit(Page, String), by the name specified on @WireVariable. If the name is absent and the field or method parameter is of type Execution, Page, Desktop, Session, or WebApp, it still will be wired to the correct implicit object. However, in other cases, an exception will be thrown.

public class FooComposer extends SelectComposer<Window> {
	
	@WireVariable
	private Page _page;
	
	@WireVariable
	private Desktop _desktop;
	
	@WireVariable
	private Session _sess;
	
	@WireVariable
	private WebApp _wapp;
	
	@WireVariable("desktopScope")
	private Map<String, Object> _desktopScope;

}

 

Wire from Variable Resolver

There are two approaches to register a variable resolver: the VariableResolver annotation or the variable-resolver directive. Here is the example of registering variable resolvers with annotations.

@VariableResolver({foo1.MyResolver.class, foo2.AnotherResolver.class})
public class FooComposer extends SelectComposer<Gird> {
....
}

To have SelectorComposer to wire a variable, you have to annotate it with the WireVariable annotation. For example,

@VariableResolver({foo1.MyResolver.class, foo2.AnotherResolver.class})
public class FooComposer extends SelectComposer<Gird> {
    @WireVariable
    Department department;
    @WireVariable
    public void setManagers(Collection<Manager> managers) {
        //...
    }
}

Wire Spring-managed Beans

If you'd like SelectorComposer to wire the Spring-managed beans, you could register the Spring variable resolver, DelegatingVariableResolver with @VariableResolver. Then, you could annotate @WireVariable for wiring a Spring managed bean. For example,

@VariableResolver(org.zkoss.zkplus.spring.DelegatingVariableResolver)
public class PasswordSetter extends SelectorComposer<Window> {
    @WireVariable
    private User user;
    @Wire
    private Textbox password; //wired automatically if there is a textbox named password

    @Listen("onClick=#submit")
    public void submit() {
        user.setPassword(password.getValue());
    }
}

DelegatingVariableResolver is a variable resolver used to retrieve the Spring-managed bean, so the variable will be retrieved and instantiated by Spring.

Notice that the variables are wired before instantiating the component and its children, so you can use them in EL expressions. For example, assume we have a composer as follows.

@VariableResolver(org.zkoss.zkplus.spring.DelegatingVariableResolver)
public class UsersComposer extends SelectorComposer<Window> {
    @WireVariable
    private List<User> users;

    public ListModel<User> getUsers() {
        return new ListModelList<User>(users);
    }
}

Then, you could reference to getUsers() in the ZUML document. For example,

<window apply="UsersComposer">
    <grid model="${$composer.users}">
...

where $composer is a built-in variable referring to the composer. For more information, please refer to the Composer section.

---

Warning: Not a good idea to have Spring managing the composer

There is a tendency to make the composer as a Spring-managed bean. For example, assume we have a composer called passwordSetter and managed by Spring, then we might do as follows.

<?variable-resolver class="org.zkoss.zkplus.spring.DelegatingVariableResolver"?>
<window apply="${passwordSetter}">
...

@Component
public class PasswordSetter extends SelectorComposer {
   @Autowired User user;
...

Unfortunately, this approach is error-prone. The reason is that none of Spring's scopes matches correctly with the lifecycle of the composers. For example, if the Session scope is used, it will cause errors when the user opens two browser windows to visit the same page. In this case, the same composer will be used to serve all desktops in the given session, and it is wrong.

The Prototype scope is a better choice since a new instance is instantiated for each request. However, it also implies another new instance will be instantiated if the Spring variable resolver is called to resolve the same name again in the later requests. It is unlikely, but it might be triggered implicitly and hard to debug. For example, it happens if some of your code evaluates an EL expression that references the composer's name, when an event received.

ZK Spring is recommended if you want to use Spring intensively. It extends Spring to provide the scopes matching ZK lifecycle, such as the IdSpace and Component scopes. Please refer to ZK Spring Essentials for more detailed information.

Wire CDI-managed Beans

The approach to work with CDI is similar to the approach for Spring, except the variable resolver for CDI is DelegatingVariableResolver.

Wiring Sequence

When extending from SelectorComposer, the fields and methods with the proper annotations will be wired automatically. Here is the sequence of wiring:

• In ComposerExt.doBeforeCompose(Page, Component, ComponentInfo), it wires variables to the fields and methods annotated with the WireVariable annotation. Here is the sequence how it looks for the variable:
  1. First, it will look for the variable resolver defined in the ZUML document first (by use of Page.addVariableResolver(VariableResolver)).
  2. Second, it looks for the variable resolver annotated at the class with the VariableResolver annotation.
  3. If none is found, it looks for the implicit objects, such as session and page.

Version History

Version	Date	Content
6.0.0	February 2012	@WireVariable was introduced.