The Personal Blog of Todd Sharp

Thymeleaf - Passing Variables From Child To Layout

Posted By: Todd Sharp on 4/7/2017 12:53 UTC
Tagged: Groovy, Spark Java, Thymeleaf
Just a quick update after my last post to clarify things a bit.  I mentioned in that post my dismay regarding the inability to pass model variables from the child view to the parent layout - and I shared that concern with the dialect developer Emanuel on GitHub.  He quickly wrote back to clarify that it is indeed possible:

Hi Todd! First of all, nice blog - I came across it the other day when you wrote about using Thymeleaf w/ Spark 

Anyway, as for passing values from child templates up to their parent layouts, it's possible using Thymeleaf's th:with attribute processors on any element that's involved in the layout/decoration process, which would be anywhere layout:decorate or layout:fragment will be found. eg:

Child/content template:

<html layout:decorate="your-layout.html" th:with="greeting='Hello!'">

Parent/layout template:

  <p th:with="${greeting}"></p> <!-- You'll end up with "Hello!" in here -->

Now, I don't seem to have documented this anywhere, and as someone who takes some pride in writing good docs, I feel a little bad that I've missed this! I swear I used to have it somewhere because others have come to me whenever this feature is broken/missing or they couldn't get it to work.

Of course I had to quickly test this out back in my Spark Java application, so I went back to the thymeleaf-layout.html view and modified it to pass the menu variable from my model into the layout:

<html xmlns:layout=""
      layout:decorate="~{fragments/main}" th:with="nav=${menu}">
Here I'm declaring that in the parent layout there should be a variable called nav that contains the value of menu from my model.  Now in the layout file (main.html) I can reference the nav variable to create my menu:

<ul class="nav navbar-nav">
    <li th:each="i : ${nav}"><a th:href="@{${i.route}}"><span th:text="${i.title}"></span></a></li>

And I'm in business!  It's great to see an open source developer so responsive and concerned with proper documentation.  Thymeleaf definitely has potential.