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For this example, we'll implement a page from an e-commerce order wizard; the page collects information
about special handling for the order:
This single screen shot doesn't capture the full richness of the user experience provided
by the Palette component. The buttons enable and disable
themselves based on what's selected. You can move items by double clicking, and you can move multiple
items by selecting
them and and then clicking the button.
This is a far better experience than using <select> with multiple enabled, as its very difficult
to navigate
a large list when using a traditional <select> and very easy to accidentally lose your selection.
The price of this
is the requirement for JavaScript on the client side.
In this contrived example, the possible types of special handling are defined using
an enum. It's more likely, in the real world, that this would be defined in terms
of a database entity.
Special Handling
]]>
Here we are able to omit the selected parameter (the list of selected items) because the Palette
component's id matches a property of the page.
The model parameter will define the available options that can be selected. The encoder parameter
will define how to translate server side values (the enum values) into client side strings and back.
handling;
@Inject
private Messages messages;
@Property
private final ValueEncoder encoder = new EnumValueEncoder(SpecialHandling.class);
@Property
private final SelectModel model = new EnumSelectModel(SpecialHandling.class, messages);
}]]>
Tapestry has built-in public classes that help convert enum types into value encoders
and select models.
Injecting a Messages object gives a component access to its own message catalog.
The Palette component will read the handling property when rendering (it's ok for it to be null).
When the form is submitted, it will create a new List and update the handling property.
The Palette can also be used to order, not just select, items, by binding the reorder
parameter to true. In that case, additional buttons are added that allow selected items to
be moved up or down the list.
The Palette can be further customized through a mix of CSS and by replacing the images
used for its various buttons.
