Basic Concepts

Fluid is a template engine that lets you display content on a website very easily. A specific file (the template) will be processed, and the containing placeholders will be replaced with the current content. This is the basic concept of template engines - as well as Fluid’s.

Fluid is based on three conceptual pillars which build the backbone of the template engine and provide for scalability and flexibility:

  • Object Accessors output the content of variables assigned to the View to be displayed.
  • ViewHelpers are special tags in the template which provide more complex functionality such as loops or generating links.
  • Arrays make it possible to assign hierarchical values to ViewHelpers.

Outputting data with object accessors

A template engine uses a placeholder to fill content in specified areas in a template, and the result is then returned to the user. In Fluid, these placeholders are called Object Accessors.


The markers used in the classic marker-based templates of TYPO3 v4 are also placeholders which are replaced later on by the desired data. You will notice, though, that the placeholders used in Fluid are clearly more flexible and versatile.

Object Accessors are written in curly brackets. For example, {blogTitle} will output the content of the variable blogTitle. The variables have to be assigned in the controller with $this->view->assign(variableName, object). Let us look at this in an example of a list of blog posts. In the controller, we assign some data to the template with the following code:

namespace ExtbaseTeam\BlogExample\Controller;
use Psr\Http\Message\ResponseInterface;

class PostController extends \TYPO3\CMS\Extbase\Mvc\Controller\ActionController
   // ...
   public function indexAction(\ExtbaseTeam\BlogExample\Domain\Model\Blog $blog): ResponseInterface
      $this->view->assign('blogTitle', 'Webdesign-Blog');
      $this->view->assign('blogPosts', $blog->getPosts());

      return $this->responseFactory->createHtmlResponse($this->view->render());

Now we can insert the string “Webdesign-Blog” into the template with the Object Accessor {blogTitle}. Let us take a look at the associated template:


 <f:for each="{blogPosts}" as="post">
     <b>{post.title}</b><br />

Upon generation of the output, the Object Accessor {blogTitle} will be replaced by the title of the blog »Webdesign-Blog«. To output the individual blog posts, the tag <f:for> is used, which you can also see in the template above. Depending on the title of each blog post, the complete output looks like this:

Example frontend output

 <b>Fluid as template-engine</b><br />
 <b>TypoScript to configure TYPO3</b><br />


If you want to output an object instead of a String, the object needs to have a __toString()-method which returns the textual representation of the object.

In the example above, you will also find the Object Accessor {post.title} which is used to output the title of a blog post. This hierarchical notation is a syntax that makes it possible to walk through associations in the object graph - you can literally move from object to object. Often, a complex object is assigned to the View, but only parts will be displayed. In the example above, we used {post.title} to display the property title of the object. Generally, Fluid tries to handle such hierarchical properties in the following order:

  • If post is an array or an object which implements the interface ArrayAccess, the corresponding property will be returned as long as it exists.
  • If it is an object, and a method getTitle() exists, the method will be called. This is the most common use case of an Object Accessor since, by convention, all public properties have a corresponding get-method.
  • The property will be returned if it exists in the object, and it is public. We discourage the ability to utilize this, though, since it violates the Uniform Access Principle (see box)

You can navigate through more complex objects because Object Accessors can be nested multiple times. For example, to output the email address of an author of a blog post, you can use {}. That’s almost equivalent to the expression $post->getAuthor()->getEmailAddress() in PHP, but focused on the essential.

Only the get-method, and not just any object method, can be called with Object Accessors. This ensures that there is no PHP code in the template. It is better to place PHP code in your own ViewHelper if needed. The following describes how to do this.

Implementing more complex functionalities with ViewHelpers

Functionalities that exceed the simple output of values have to be implemented with ViewHelpers. Every ViewHelper has its own PHP class. Now, we’re going to see how we can use ViewHelpers. Later, you’ll also learn how to write your own ViewHelper.

To use an existing ViewHelper, you have to import the namespace and assign a shortcut to it. You can do this with the declaration {namespace ...=...}.

All namespaces used in your template must always be registered. This might seem redundant, but because all important information is embedded in the template, readability increases immensely for other template editors who work on the same templates.

The standard ViewHelper of Fluid will be imported and assigned to the shortcut f with the following declaration:

 {namespace f=TYPO3\CMS\Fluid\ViewHelpers}

This namespace will be imported automatically by Fluid. All ViewHelpers that come with Fluid are prefixed with f. Your own namespaces have to be imported into the template like previously mentioned.

All tags, which begin with a registered prefix, will be evaluated. Here’s a small example:

     <f:for each="{blogPosts}" as="post">

Tags without a registered prefix (in this example <ul> and <li>) will be treated as text. The tag <f:for> will be interpreted as a ViewHelper since it starts with the prefix f:. This is implemented in the class \TYPO3Fluid\Fluid\ViewHelpers\ForViewHelper.

The first part of the class name is the complete namespace like it was defined earlier with {namespace f=TYPO3\CMS\Fluid\ViewHelpers}. Followed by the name of the ViewHelper and the ending ViewHelper.

Fluid will interpret every argument of a ViewHelper. The ViewHelper <f:for> from the previous example therefore receives the array of all blog posts with the argument each.


If the name of the ViewHelper contains a single or multiple periods, it will be resolved as a subpackage. For example, the ViewHelper f:form.textfield is implemented in the class \TYPO3\CMS\Fluid\ViewHelpers\Form\TextfieldViewHelper. Therefore ViewHelpers can be divided further and structured even more.

ViewHelpers are the main tools of template editors. They make it possible to have a clear separation of the template and embedded functionality.


All control structures like if/else or for are individual ViewHelpers in Fluid and not a core language feature. This is one of the main reasons for the flexibility of Fluid. You’ll find a detailed reference in the ViewHelpers Reference.

Flexible array data structures

Arrays round off the concept of Fluid and build another core concept of the template engine. Arrays in Fluid can be somewhat compared to associative arrays in PHP. Every value in a Fluid array needs a key.

Arrays are used to pass a variable number of arguments to View Helpers. The best example is the link.action-ViewHelper. With this, you can create a link to other controllers and Actions in your Extension. The following link refers to the index action of the Post controller:

<f:link.action controller="Post" action="index">
    Show list of all posts

However, many links in your application need parameters, which can be passed with the arguments attribute. We can already see that we need arrays to do so: It’s unpredictable how many parameters you want to pass. By using an array, we can pass an indefinite amount of parameters. The following example adds the parameter post to the link:

<f:link.action controller="Post" action="show" arguments="{post: currentPost}">
   Show current post

The array {post: currentPost} consists of a single element with the name post. The value of the element is the object currentPost. A comma separates multiple elements: {post: currentPost, blogTitle: 'Webdesign-Blog'}.

Fluid only supports named arrays, which means that you always have to specify the key of the array element. Let’s look at what options you have when creating an array:

Example array in Fluid
     key1: 'Hello',
     key2: "World",
     key3: 20,
     key4: blog,
     key5: blog.title,
     key6: '{firstname} {lastname}'

The array can contain strings as values as in key1 and key2. It can also have numbers as values as in key3. More interesting are key4 and key5: Object Accessors are being specified as array values. You can also access sub-objects like you are used to with Object Accessors. All strings in arrays are interpreted as Fluid markup as well. So that you can combine strings from individual strings, for example. This way, it is also possible to call ViewHelpers with the inline notation.

These are the basic concepts of Fluid. Now we move on to more advanced concepts, which increase the effectiveness of template creation. The following chapter will explain how to use different output formats to achieve different views of data.