` tag, this would be the result: .. code-block:: html

content

Boolean attributes ------------------ You can use the boolean literals `{true}` and `{false}` to enable or disable attributes of tag-based ViewHelpers: .. code-block:: xml Result:

Result:

Of course, any variable containing a boolean can be supplied as well: .. code-block:: xml It is also possible to cast a string to a boolean: .. code-block:: xml For backwards compatibility, empty strings still lead to the attribute being omitted from the tag: .. code-block:: xml Result:

.. _condition-viewhelpers: Condition ViewHelpers ===================== Condition ViewHelpers are another special type of ViewHelper that allow to check for certain conditions within a template. They extend from a different base class called `AbstractConditionViewHelper `_. All condition ViewHelpers have in common that a `then` and one or multiple `else` clauses can be defined. There are multiple ways to do this, and almost all combinations imaginable are possible. The generic and most used condition ViewHelper is :ref:`

`. then/else as argument --------------------- You can define `then` and `else` as ViewHelper arguments: .. code-block:: xml {f:if(condition: '{myVar} == \'test\'', then: 'variable is test', else: 'variable is something else')} {f:if(condition: '{myVar} == \'test\'', then: 'variable is test')} {f:if(condition: '{myVar} == \'test\'', else: 'variable is something else')} then/else as child ViewHelpers ------------------------------ With the tag syntax, it is also possible to define more advanced conditions: .. code-block:: xml variable is test variable is test variable is something else variable is something else variable is test variable is foo variable is bar variable is something else Get verdict by omitting then/else --------------------------------- .. versionadded:: Fluid 4.1 If neither `then` nor `else` in any of the accepted forms is specified, the ViewHelper returns the verdict of the condition as boolean. This value can be used for further processing in the template, for example in complex conditions: .. code-block:: xml ... This syntax can also be helpful in combination with a `Tag-Based ViewHelper `_: .. code-block:: xml .. _understanding-viewhelpers: Understanding ViewHelpers ========================= All built-in ViewHelpers are documented in the :ref:`ViewHelper Reference `. If you want to learn more about a specific ViewHelper or if you are using a custom ViewHelper that isn't documented, you can take a look at the ViewHelper source code, written in PHP. Each ViewHelper has a corresponding PHP file, which contains a class that describes the ViewHelper's arguments as well as its behavior in the template. Such classes are usually placed in the `Vendor\Package\ViewHelpers` PHP namespace (where `Vendor` and `Package` are placeholders for actual values) and follow the following naming convention: * `f:format.raw` results from the PHP class :php:`TYPO3Fluid\Fluid\ViewHelpers\Format\RawViewHelper` * `f:render` results from the PHP class :php:`TYPO3Fluid\Fluid\ViewHelpers\RenderViewHelper` * `mypkg:custom.specialFormat` results from the PHP class :php:`My\Package\ViewHelpers\Custom\SpecialFormatViewHelper`, assuming you added `xmlns:mpkg="http://typo3.org/ns/My/Package/ViewHelpers"` or an alternative namespace registration (see above). The arguments a ViewHelper supports will be verbosely registered in the `initializeArguments()` function of each ViewHelper class. Inspect this method to see the names, types, descriptions, required flags and default values of all attributes. An example argument definition looks like this: .. code-block:: php public function initializeArguments() { $this->registerArgument('myArgument', 'boolean', 'If true, makes ViewHelper do foobar', false, false); } Which translated to human terms means that we: * Register an argument named `myArgument` * Specify that it must be a boolean value or an expression resulting in a boolean value (see :ref:`Boolean conditions `). Other valid types are `integer`, `string`, `float`, `array`, `object`, `DateTime` and other class names. The *array of* syntax can also be used, for example `string[]` or `Vendor\Package\MyClass[]`. * Describe the argument's behavior in simple terms. * Define that the argument is not required (the 4th argument is :php:`false`). * Set a default value of :php:`false` (5th argument), if the argument is not provided when calling the ViewHelper. The ViewHelper itself would then be callable like this: .. code-block:: xml {someVariable} What the ViewHelper does with its input values is determined by the `render()` method in the ViewHelper class.