Checklist (Tapestry API Documentation)

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org.apache.tapestry5.corelib.components
Class Checklist

java.lang.Object
  org.apache.tapestry5.corelib.base.AbstractField
      org.apache.tapestry5.corelib.components.Checklist

All Implemented Interfaces:: ClientElement, Field

public class Checklist
extends AbstractField
extends AbstractField

A list of checkboxes, allowing selection of multiple items in a list.

For an alternative component that can be used for similar purposes, see Palette.

Since:: 5.3
See Also:: Form, Palette

Component Parameters
Name	Description	Type	Flags	Default	Default Prefix	Since
clientId	The id used to generate a page-unique client-side identifier for the component. If a component renders multiple times, a suffix will be appended to the to id to ensure uniqueness. The uniqued value may be accessed via the clientId property.	String		prop:componentResources.id	literal
disabled	If true, then the field will render out with a disabled attribute (to turn off client-side behavior). When the form is submitted, the bound value is evaluated again and, if true, the field's value is ignored (not even validated) and the component's events are not fired.	boolean		false	prop
encoder	A ValueEncoder used to convert server-side objects (provided from the "source" parameter) into unique client-side strings (typically IDs) and back. Note: this component does NOT support ValueEncoders configured to be provided automatically by Tapestry.	org.apache.tapestry5.ValueEncoder	Required, Not Null		prop
label	The user presentable label for the field. If not provided, a reasonable label is generated from the component's id, first by looking for a message key named "id-label" (substituting the component's actual id), then by converting the actual id to a presentable string (for example, "userId" to "User Id").	String			literal
model	Model used to define the values and labels used when rendering the checklist.	org.apache.tapestry5.SelectModel	Required		prop
selected	The list of selected values from the org.apache.tapestry5.SelectModel. This will be updated when the form is submitted. If the value for the parameter is null, a new list will be created, otherwise the existing list will be cleared. If unbound, defaults to a property of the container matching this component's id.	java.util.List	Required		prop
validate	The object that will perform input validation. The validate binding prefix is generally used to provide this object in a declarative fashion.	org.apache.tapestry5.FieldValidator			validate

Examples:

For this example, we'll implement a page from an e-commerce order wizard; the page collects information about special handling for the order:

SpecialHandling.java

Now let's see how the component can be used.

public enum SpecialHandling
{
    EXPRESS_SERVICE, GIFT_WRAP, GIFT_BASKET, CUSTOM_ENGRAVING, SHIPPING_INSURANCE,
    EXTENDED_WARRANTY
}

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.

OrderHandling.tml

<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_3.xsd">
    <body>
        <h1>Special Handling</h1>

        <t:form>

            <t:checklist t:id="handling" encoder="encoder" model="model"/>

            <br/>

            <input type="submit" value="Continue"/>

        </t:form>

    </body>
</html>

Here we are able to omit the selected parameter (the list of selected items) because the Checklist 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.

OrderHandling.java

public class OrderHandling {
    @Property
    @Persist
    private List<SpecialHandling> handling;

    @Inject
    private Messages messages;

    public ValueEncoder getEncoder() {
        return new EnumValueEncoder(SpecialHandling.class);
    }

    public SelectModel getModel() {
        return 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 Checklist 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.

Notes:

The Checklist component can be customized through CSS. Following CSS rules are used:

t-checklist-row: Each checkbox and its label is enclosed by a div element whose css attribute is set to t-checklist-row.

Constructor Summary
`Checklist()`

Method Summary
`boolean`	`isRequired()` Returns false; most components do not support declarative validation.
`protected void`	`processSubmission(String controlName)` Method implemented by subclasses to actually do the work of processing the submission of the form.

Methods inherited from class org.apache.tapestry5.corelib.base.AbstractField
`decorateInsideField, getClientId, getControlName, getLabel, isDisabled, putPropertyNameIntoBeanValidationContext, removePropertyNameFromBeanValidationContext, setDecorator, setFormSupport`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

Checklist

public Checklist()

Method Detail

processSubmission

protected void processSubmission(String controlName)

Description copied from class: AbstractField

Method implemented by subclasses to actually do the work of processing the submission of the form. The element's controlName property will already have been set. This method is only invoked if the field is not disabled.

Specified by:: processSubmission in class AbstractField

Parameters:: controlName - the control name of the rendered element (used to find the correct parameter in the request)

isRequired

public boolean isRequired()