Super-Easy DropDownChoice Renderer for String values

Too often you may find yourself writing a simple selection list in Wicket.

Whether you know your list values in advance or not, you’ll soon fight with some rendering issue involved with your select component.

Wicket puts at your service the good old DropDownChoice component; good enough to do the job, but it usually force you to use a compound object as its model; If you want to use a simple list of Strings you’ll have to figure out for yourself how to handle “id” and “value” visualization; If not instructed other-way, Wicket will use the “toString” for your object as the display value and its index in the list as its option value.

//DataObject is come kind of value object having the String property "value"...
List<String> values = Arrays.asList( "value_1", "value_2" );
add( new DropDownChoice<String>("my_wicket_id",
                 new PropertyModel<String>(myDataObject, "value"), values ) );

In the preceding code bit, you’ll get a selection list having options with id=1,2,3.. and displayed values of “value_1″, “value_2″..

If you are happy in using the option index as the actual key and/or you don’t have any localization requirement you can be satisfied with it; Otherwise, here’s a very simple yet effective solution to manage the localization thing and keeping the power to choose what information to use as the option key:

public class StringBasedChoiceRenderer implements IChoiceRenderer<String>{
    private static final long serialVersionUID = 1L;
    String context;

    /**
     *
     * @param context can be your wicketId or any other string you desire.
     * this value is used as a prefix in order to get the localized option value.
     */
    public StringBasedChoiceRenderer( String context )
    {
        this.context = context;
    }
    /**
     * To obtain the display value we localize the string obtained concatenating
     * the constructor context value and the actual value of the option.
     */
    public Object getDisplayValue(String object)
    {
        return new ResourceModel( context + "." + object, object ).getObject();
    }

    /**
     * This basic implementation use the entire string value as the option key
     */
    public String getIdValue(String object, int index)
    {
        return object;
    }
}

Using this class is super easy:

List<String> values = Arrays.asList( "value_1", "value_2" );

add( new DropDownChoice<String>("my_wicket_id",
                 new PropertyModel<String>(myDataObject, "value"), values,
                 new StringBasedChoiceRenderer( "options.value" ) ) );

You’ll have, obviously, to add localization strings to your Application property file. NOTE: you have to put localized strings in your Application-wide property files because the renderes uses ResourceModel and it’s not bound to any component:

options.value.value_1=First Value
options.value.value_2=Second Value

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