Advanced usage of helpers

Registering Helpers

Zend\View\Renderer\PhpRenderer composes a plugin manager for managing helpers, specifically an instance of Zend\View\HelperPluginManager, which extends Zend\ServiceManager\AbstractPluginManager, which is itself an extension of Zend\ServiceManager\ServiceManager. HelperPluginManager is a specialized service manager, so you can register a helper/plugin like any other service (see the Service Manager documentation for more information).

Programmatically, this is done as follows:

use MyModule\View\Helper\LowerCase;

// $view is an instance of PhpRenderer
$pluginManager = $view->getHelperPluginManager();

// Register an alias:
$pluginManager->setAlias('lowercase', LowerCase::class);

// Register a factory:
$pluginManager->setFactory(LowerCase::class, function () {
   $lowercaseHelper = new LowerCase();

   // ...do some configuration or dependency injection...

   return $lowercaseHelper;
});

Within an MVC application, you will typically pass a map of plugins to the class via your configuration.

use MyModule\View\Helper;
use Zend\ServiceManager\Factory\InvokableFactory;

// From within a configuration file
return [
   'view_helpers' => [
        'aliases' => [
            'lowercase' => Helper\LowerCase::class,
            'uppercase' => Helper\UpperCase::class,
        ],
        'factories' => [
            LowerCase::class => InvokableFactory::class,
            UpperCase::class => InvokableFactory::class,
        ],
    ],
];

If your module class implements Zend\ModuleManager\Feature\ViewHelperProviderInterface, or just the method getViewHelperConfig(), you could also do the following (it's the same as the previous example).

namespace MyModule;

class Module
{
    public function getViewHelperConfig()
    {
        return [
            'aliases' => [
                'lowercase' => Helper\LowerCase::class,
                'uppercase' => Helper\UpperCase::class,
            ],
            'factories' => [
                LowerCase::class => InvokableFactory::class,
                UpperCase::class => InvokableFactory::class,
            ],
        ];
    }
}

The two latter examples can be done in each module that needs to register helpers with the PhpRenderer; however, be aware that another module can register helpers with the same name, so order of modules can impact which helper class will actually be registered!

Writing Custom Helpers

Writing custom helpers is easy. We recommend extending Zend\View\Helper\AbstractHelper, but at the minimum, you need only implement the Zend\View\Helper\HelperInterface interface:

namespace Zend\View\Helper;

use Zend\View\Renderer\RendererInterface as Renderer;

interface HelperInterface
{
    /**
     * Set the View object
     *
     * @param  Renderer $view
     * @return HelperInterface
     */
    public function setView(Renderer $view);

    /**
     * Get the View object
     *
     * @return Renderer
     */
    public function getView();
}

If you want your helper to be capable of being invoked as if it were a method call of the PhpRenderer, you should also implement an __invoke() method within your helper.

As previously noted, we recommend extending Zend\View\Helper\AbstractHelper, as it implements the methods defined in HelperInterface, giving you a headstart in your development.

Invokable helpers

Starting with version 2.7.0, helpers no longer need to be instances of HelperInterface, but can be any PHP callable. We recommend writing helpers as invokable classes (classes implementing __invoke().

Once you have defined your helper class, make sure you can autoload it, and then register it with the plugin manager.

Here is an example helper, which we're titling "SpecialPurpose"

namespace MyModule\View\Helper;

use Zend\View\Helper\AbstractHelper;

class SpecialPurpose extends AbstractHelper
{
    protected $count = 0;

    public function __invoke()
    {
        $this->count++;
        $output = sprintf("I have seen 'The Jerk' %d time(s).", $this->count);
        return htmlspecialchars($output, ENT_QUOTES, 'UTF-8');
    }
}

Then assume that we register it with the plugin manager by the name "specialpurpose".

Within a view script, you can call the SpecialPurpose helper as many times as you like; it will be instantiated once, and then it persists for the life of that PhpRenderer instance.

// remember, in a view script, $this refers to the Zend\View\Renderer\PhpRenderer instance.
echo $this->specialPurpose();
echo $this->specialPurpose();
echo $this->specialPurpose();

The output would look something like this:

I have seen 'The Jerk' 1 time(s).
I have seen 'The Jerk' 2 time(s).
I have seen 'The Jerk' 3 time(s).

Sometimes you will need access to the calling PhpRenderer object; for instance, if you need to use the registered encoding, or want to render another view script as part of your helper. This is why we define the setView() and getView() methods. As an example, we could rewrite the SpecialPurpose helper as follows to take advantage of the EscapeHtml helper:

namespace MyModule\View\Helper;

use Zend\View\Helper\AbstractHelper;

class SpecialPurpose extends AbstractHelper
{
    protected $count = 0;

    public function __invoke()
    {
        $this->count++;
        $output  = sprintf("I have seen 'The Jerk' %d time(s).", $this->count);
        $escaper = $this->getView()->plugin('escapehtml');
        return $escaper($output);
    }
}

Accessing the view or other helpers in callables

As noted earlier, starting in version 2.7.0, you may use any PHP callable as a helper. If you do, however, how can you access the renderer or other plugins?

The answer is: dependency injection.

If you write your helper as a class, you can accept dependencies via the constructor or other setter methods. Create a factory that pulls those dependencies and injects them.

As an example, if we need the escapeHtml() helper, we could write our helper as follows:

namespace MyModule\View\Helper;

use Zend\View\Helper\EscapeHtml;

class SpecialPurpose
{
    private $count = 0;

    private $escaper;

    public function __construct(EscapeHtml $escaper)
    {
        $this->escaper = $escaper;
    }

    public function __invoke()
    {
        $this->count++;
        $output  = sprintf("I have seen 'The Jerk' %d time(s).", $this->count);
        $escaper = $this->escaper;
        return $escaper($output);
    }
}

Then we would write a factory like the following:

use Zend\ServiceManager\AbstractPluginManager;

class SpecialPurposeFactory
{
    public function __invoke($container)
    {
        if (! $container instanceof AbstractPluginManager) {
            // zend-servicemanager v3. v2 passes the helper manager directly.
            $container = $container->get('ViewHelperManager');
        }

        return new SpecialPurpose($container->get('escapeHtml'));
    }
}

If access to the view were required, we'd pass the PhpRenderer service instead.

Registering Concrete Helpers

Sometimes it is convenient to instantiate a view helper, and then register it with the renderer. This can be done by injecting it directly into the plugin manager.

// $view is a PhpRenderer instance

$helper = new MyModule\View\Helper\LowerCase;
// ...do some configuration or dependency injection...

$view->getHelperPluginManager()->setService('lowercase', $helper);

The plugin manager will validate the helper/plugin, and if the validation passes, the helper/plugin will be registered.