Question

Hi I have a problem about dynamically displaying the value of a HtmlSelectOneMenu. Below is a small application that describes my problem.

I have a list of cars List<Car> carList = new ArrayList<Car>() in my backing bean.

Car is a abstract class and Toyota and Ford extends Car.

Now I need to display different message in the selectonemenu based on the class type. If it is Toyota then I would display something else. Maybe its clearer for the codes to tell the story.

Backing Bean:

@ManagedBean(name="myBean")
@SessionScoped
public class MyCarBackingBean implements PhaseListener {

    private List<Car> carList = new ArrayList<Car>();
    private HtmlSelectOneMenu hsom;
    Car myCar;

    @PostConstruct
    public void init() {
        carList.add(new Ford());
        carList.add(new Toyota());
    }


    @Override
    public void beforePhase(PhaseEvent event) {
    //hsom becomes null here. Im pretty sure the setHsom was called before and the variable was set.
    if(hsom != null) {
        switch((Integer)hsom.getValue()){
            case 1: hsom.setValue("This is a Ford car"); break;
            case 2: hsom.setValue("This is a Toyota car"); 
        }
    }


    //The rest of the world...
}

And i bind the selectonemenu to the component in my page:

<h:form>
    <h:selectOneMenu binding="#{myBean.hsom}">
       <f:selectItems value="#{myBean.carList}" var="car" itemValue="#{car.id}" itemLabel="#{car.id}" />
       </h:selectOneMenu>
    <h:commandButton value="Submit" action="#{myBean.mySubmit()}"/>
</h:form>

And finally the model classes:

public abstract class Car {

    protected int id;
    //Getters and Setters

}

public class Toyota extends Car {

    public Toyota(){
        this.id = 2; //in case of ford car, id is 1.
    }

}

And I’m thinking using a phase listener to change the display, cos I read some posts saying that it is bad to change the getters and setters and put business logic in them. Nor do I want to wrap those cars in other objects and make use of itemLabel and itemValue.

But when I was debugging it I found that hsom is null when the execution reaches beforePhase but it is not null in the rest part of the code.

So my questions are : is it a good way to use a phase listener for this? And why is the component object null in beforePhase?

Answer 1

Add a different attribute (say description) to your class. Implement it as you like, and refer to it in the selectItems tag. V.g.

<f:selectItems value="#{myBean.carList}" var="car" itemValue="#{car.id}" itemLabel="#{car.description}" />

Alternatively, replace myBean.carList with a method that returns a List<SelectItem>, and create the selectItems as you wish.

As a rule of thumb, try to keep the .xhtml as “logic-free” as possible.