Tapestry RadioGroup with radio button in loop

Question

Using tapestry 5.6.2

I want to do something like this

<t:loop t:source="orders" t:value="order">
    <t:RadioGroup name="shipping">

      <t:loop t:source="order.shippingOptions" value="shippingOption">
         <t:Radio value="shippingOption"/>
         <t:Label for="????">${shippingOption.description}<strong>${shippingOption.cost} 
              </strong></t:Label>
      </t:loop>
    </t:RadioGroup>
</t:loop>

The problem is that i can't anticipate which id is the Radio going to take and put it in the "for" parameter of the label

I tried making something like <t:radio id="${shippingOptionId}"...

and implement a "public String getShippingOptionId()" on the java side but that parameter is ignored

lance-java · Accepted Answer · 2025-08-26 15:27:57Z

Tapestry will use a single instance of the Radio component to render the entire group. So the t:id will be the same for all items in the loop.

You should just be able to do

<t:RadioGroup name="shipping">
  <t:loop source="order.shippingOptions" value="shippingOption" encoder="myEncoder">
    <t:Radio t:id="shippingOption" value="shippingOption.value"/>
    <t:Label for="shippingOption">${shippingOption.description} ${shippingOption.cost}</t:Label>
  </t:loop>
</t:RadioGroup>

Note this requires a custom ValueEncoder

From the loop docs

In general, when using a non-volatile Loop in a Form, you should either provide a ValueEncoder with the encoder parameter or use a "value" type for which Tapestry is configured to provide a ValueEncoder automatically.

See the "Forms and Loops Example" in the Loop Docs

<t:loop source="items" value="item" encoder="encoder">
  <div class="line-item">
    <t:label for="quantity">${item.product.name}</t:label>
    <t:textfield t:id="quantity" value="item.quantity"/>
  </div>
</t:loop>

Note: You can't use ${...} notation for tapestry component attributes but you can use a binding prefix.

Instead of <t:foo value="${x.y.z}" />

You could do <t:foo value="prop:x.y.z" />

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