Why doesn't th:checked work with th:field?

[ShedowSith]

There is such a block of code for displaying checkboxes:

<th:block th:each="type:${types}"> <label class="list-group-item"> <input class="form-check-input me-1" type="checkbox" th:value="${type.getId()}" th:field="*{types}" th:checked="${selectType.contains(type)}"> <span th:text="${type.name}"></span> </label> </th:block>

On form load the checkboxes are not set as selected, if I remove th:field everything is displayed, but without th:field I can't pass the form data to the controller. What is the problem?

[ultraq]

Looking at the checkbox examples in the docs (https://www.thymeleaf.org/doc/tutorials/3.0/thymeleafspring.html#checkbox-fields), it looks like what you need to get a checkbox backed by form data is th:field and th:value. A checked attribute will be added by Thymeleaf if the value is considered selected/true, so you don't need to provide one yourself.

Given that, your <input> might need to look more like the following:

<input class="form-check-input me-1" type="checkbox" th:field="*{types}" th:value="${type}">

I found another example here, part 2.3, which includes how it all lines up with the backing bean: https://frontbackend.com/thymeleaf/working-with-forms-in-thymeleaf

[ShedowSith]

thanks a lot, everything worked. It turns out that the field that I pass to th : field should contain an array of selected elements