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Class yii\filters\PageCache

Inheritanceyii\filters\PageCache » yii\base\ActionFilter » yii\base\Behavior » yii\base\BaseObject
Implementsyii\base\Configurable, yii\base\DynamicContentAwareInterface
Uses Traitsyii\base\DynamicContentAwareTrait
Available since version2.0
Source Code https://github.com/yiisoft/yii2/blob/master/framework/filters/PageCache.php

PageCache implements server-side caching of whole pages.

It is an action filter that can be added to a controller and handles the beforeAction event.

To use PageCache, declare it in the behaviors() method of your controller class. In the following example the filter will be applied to the index action and cache the whole page for maximum 60 seconds or until the count of entries in the post table changes. It also stores different versions of the page depending on the application language.

public function behaviors()
{
    return [
        'pageCache' => [
            'class' => 'yii\filters\PageCache',
            'only' => ['index'],
            'duration' => 60,
            'dependency' => [
                'class' => 'yii\caching\DbDependency',
                'sql' => 'SELECT COUNT(*) FROM post',
            ],
            'variations' => [
                \Yii::$app->language,
            ]
        ],
    ];
}

Public Properties

Hide inherited properties

Property Type Description Defined By
$cache yii\caching\CacheInterface|array|string The cache object or the application component ID of the cache object. yii\filters\PageCache
$cacheCookies boolean|array A boolean value indicating whether to cache all cookies, or an array of cookie names indicating which cookies can be cached. yii\filters\PageCache
$cacheHeaders boolean|array A boolean value indicating whether to cache all HTTP headers, or an array of HTTP header names (case-sensitive) indicating which HTTP headers can be cached. yii\filters\PageCache
$dependency array|yii\caching\Dependency The dependency that the cached content depends on. yii\filters\PageCache
$duration integer Number of seconds that the data can remain valid in cache. yii\filters\PageCache
$dynamicPlaceholders array A list of placeholders. yii\base\DynamicContentAwareTrait
$enabled boolean Whether to enable the page cache. yii\filters\PageCache
$except array List of action IDs that this filter should not apply to. yii\base\ActionFilter
$only array List of action IDs that this filter should apply to. yii\base\ActionFilter
$owner yii\base\Component|null The owner of this behavior yii\base\Behavior
$variations string[]|string List of factors that would cause the variation of the content being cached. yii\filters\PageCache
$varyByRoute boolean Whether the content being cached should be differentiated according to the route. yii\filters\PageCache
$view yii\base\View|null The view component to use for caching. yii\filters\PageCache

Public Methods

Hide inherited methods

Method Description Defined By
__call() Calls the named method which is not a class method. yii\base\BaseObject
__construct() Constructor. yii\base\BaseObject
__get() Returns the value of an object property. yii\base\BaseObject
__isset() Checks if a property is set, i.e. defined and not null. yii\base\BaseObject
__set() Sets value of an object property. yii\base\BaseObject
__unset() Sets an object property to null. yii\base\BaseObject
addDynamicPlaceholder() Adds a placeholder for dynamic content. yii\base\DynamicContentAwareTrait
afterAction() This method is invoked right after an action is executed. yii\base\ActionFilter
afterFilter() yii\base\ActionFilter
afterRestoreResponse() This method is invoked right after the response restoring is finished (but before the response is sent). yii\filters\PageCache
attach() Attaches the behavior object to the component. yii\base\ActionFilter
beforeAction() This method is invoked right before an action is to be executed (after all possible filters.) You may override this method to do last-minute preparation for the action. yii\filters\PageCache
beforeCacheResponse() This method is invoked right before the response caching is to be started. yii\filters\PageCache
beforeFilter() yii\base\ActionFilter
cacheResponse() Caches response properties. yii\filters\PageCache
canGetProperty() Returns a value indicating whether a property can be read. yii\base\BaseObject
canSetProperty() Returns a value indicating whether a property can be set. yii\base\BaseObject
className() Returns the fully qualified name of this class. yii\base\BaseObject
detach() Detaches the behavior object from the component. yii\base\ActionFilter
events() Declares event handlers for the $owner's events. yii\base\Behavior
getDynamicPlaceholders() Returns a list of placeholders for dynamic content. This method is used internally to implement the content caching feature. yii\base\DynamicContentAwareTrait
getView() yii\filters\PageCache
hasMethod() Returns a value indicating whether a method is defined. yii\base\BaseObject
hasProperty() Returns a value indicating whether a property is defined. yii\base\BaseObject
init() Initializes the object. yii\filters\PageCache
setDynamicPlaceholders() Sets a list of placeholders for dynamic content. This method is used internally to implement the content caching feature. yii\base\DynamicContentAwareTrait

Protected Methods

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Method Description Defined By
calculateCacheKey() yii\filters\PageCache
getActionId() Returns an action ID by converting yii\base\Action::$uniqueId into an ID relative to the module. yii\base\ActionFilter
isActive() Returns a value indicating whether the filter is active for the given action. yii\base\ActionFilter
restoreResponse() Restores response properties from the given data. yii\filters\PageCache
updateDynamicContent() Replaces placeholders in $content with results of evaluated dynamic statements. yii\base\DynamicContentAwareTrait

Constants

Hide inherited constants

Constant Value Description Defined By
PAGE_CACHE_VERSION 1 Page cache version, to detect incompatibilities in cached values when the data format of the cache changes. yii\filters\PageCache

Property Details

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$cache public property

The cache object or the application component ID of the cache object. After the PageCache object is created, if you want to change this property, you should only assign it with a cache object. Starting from version 2.0.2, this can also be a configuration array for creating the object.

$cacheCookies public property (available since version 2.0.4)

A boolean value indicating whether to cache all cookies, or an array of cookie names indicating which cookies can be cached. Be very careful with caching cookies, because it may leak sensitive or private data stored in cookies to unwanted users.

public boolean|array $cacheCookies false
$cacheHeaders public property (available since version 2.0.4)

A boolean value indicating whether to cache all HTTP headers, or an array of HTTP header names (case-sensitive) indicating which HTTP headers can be cached. Note if your HTTP headers contain sensitive information, you should white-list which headers can be cached.

public boolean|array $cacheHeaders true
$dependency public property

The dependency that the cached content depends on. This can be either a yii\caching\Dependency object or a configuration array for creating the dependency object. For example,

[
    'class' => 'yii\caching\DbDependency',
    'sql' => 'SELECT MAX(updated_at) FROM post',
]

would make the output cache depend on the last modified time of all posts. If any post has its modification time changed, the cached content would be invalidated.

If $cacheCookies or $cacheHeaders is enabled, then yii\caching\Dependency::$reusable should be enabled as well to save performance. This is because the cookies and headers are currently stored separately from the actual page content, causing the dependency to be evaluated twice.

$duration public property

Number of seconds that the data can remain valid in cache. Use 0 to indicate that the cached data will never expire.

public integer $duration 60
$enabled public property

Whether to enable the page cache. You may use this property to turn on and off the page cache according to specific setting (e.g. enable page cache only for GET requests).

public boolean $enabled true
$variations public property

List of factors that would cause the variation of the content being cached. Each factor is a string representing a variation (e.g. the language, a GET parameter). The following variation setting will cause the content to be cached in different versions according to the current application language:

[
    Yii::$app->language,
]
public string[]|string $variations null
$varyByRoute public property

Whether the content being cached should be differentiated according to the route. A route consists of the requested controller ID and action ID. Defaults to true.

public boolean $varyByRoute true
$view public property

The view component to use for caching. If not set, the default application view component yii\web\Application::$view will be used.

public yii\base\View|null $view null

Method Details

Hide inherited methods

__call() public method

Defined in: yii\base\BaseObject::__call()

Calls the named method which is not a class method.

Do not call this method directly as it is a PHP magic method that will be implicitly called when an unknown method is being invoked.

public mixed __call ( $name, $params )
$name string

The method name

$params array

Method parameters

return mixed

The method return value

throws yii\base\UnknownMethodException

when calling unknown method

                public function __call($name, $params)
{
    throw new UnknownMethodException('Calling unknown method: ' . get_class($this) . "::$name()");
}

            
__construct() public method

Defined in: yii\base\BaseObject::__construct()

Constructor.

The default implementation does two things:

  • Initializes the object with the given configuration $config.
  • Call init().

If this method is overridden in a child class, it is recommended that

  • the last parameter of the constructor is a configuration array, like $config here.
  • call the parent implementation at the end of the constructor.
public void __construct ( $config = [] )
$config array

Name-value pairs that will be used to initialize the object properties

                public function __construct($config = [])
{
    if (!empty($config)) {
        Yii::configure($this, $config);
    }
    $this->init();
}

            
__get() public method

Defined in: yii\base\BaseObject::__get()

Returns the value of an object property.

Do not call this method directly as it is a PHP magic method that will be implicitly called when executing $value = $object->property;.

See also __set().

public mixed __get ( $name )
$name string

The property name

return mixed

The property value

throws yii\base\UnknownPropertyException

if the property is not defined

throws yii\base\InvalidCallException

if the property is write-only

                public function __get($name)
{
    $getter = 'get' . $name;
    if (method_exists($this, $getter)) {
        return $this->$getter();
    } elseif (method_exists($this, 'set' . $name)) {
        throw new InvalidCallException('Getting write-only property: ' . get_class($this) . '::' . $name);
    }
    throw new UnknownPropertyException('Getting unknown property: ' . get_class($this) . '::' . $name);
}

            
__isset() public method

Defined in: yii\base\BaseObject::__isset()

Checks if a property is set, i.e. defined and not null.

Do not call this method directly as it is a PHP magic method that will be implicitly called when executing isset($object->property).

Note that if the property is not defined, false will be returned.

See also https://www.php.net/manual/en/function.isset.php.

public boolean __isset ( $name )
$name string

The property name or the event name

return boolean

Whether the named property is set (not null).

                public function __isset($name)
{
    $getter = 'get' . $name;
    if (method_exists($this, $getter)) {
        return $this->$getter() !== null;
    }
    return false;
}

            
__set() public method

Defined in: yii\base\BaseObject::__set()

Sets value of an object property.

Do not call this method directly as it is a PHP magic method that will be implicitly called when executing $object->property = $value;.

See also __get().

public void __set ( $name, $value )
$name string

The property name or the event name

$value mixed

The property value

throws yii\base\UnknownPropertyException

if the property is not defined

throws yii\base\InvalidCallException

if the property is read-only

                public function __set($name, $value)
{
    $setter = 'set' . $name;
    if (method_exists($this, $setter)) {
        $this->$setter($value);
    } elseif (method_exists($this, 'get' . $name)) {
        throw new InvalidCallException('Setting read-only property: ' . get_class($this) . '::' . $name);
    } else {
        throw new UnknownPropertyException('Setting unknown property: ' . get_class($this) . '::' . $name);
    }
}

            
__unset() public method

Defined in: yii\base\BaseObject::__unset()

Sets an object property to null.

Do not call this method directly as it is a PHP magic method that will be implicitly called when executing unset($object->property).

Note that if the property is not defined, this method will do nothing. If the property is read-only, it will throw an exception.

See also https://www.php.net/manual/en/function.unset.php.

public void __unset ( $name )
$name string

The property name

throws yii\base\InvalidCallException

if the property is read only.

                public function __unset($name)
{
    $setter = 'set' . $name;
    if (method_exists($this, $setter)) {
        $this->$setter(null);
    } elseif (method_exists($this, 'get' . $name)) {
        throw new InvalidCallException('Unsetting read-only property: ' . get_class($this) . '::' . $name);
    }
}

            
addDynamicPlaceholder() public method

Defined in: yii\base\DynamicContentAwareTrait::addDynamicPlaceholder()

Adds a placeholder for dynamic content.

This method is used internally to implement the content caching feature.

public void addDynamicPlaceholder ( $name, $statements )
$name string

The placeholder name.

$statements string

The PHP statements for generating the dynamic content.

                public function addDynamicPlaceholder($name, $statements)
{
    $this->_dynamicPlaceholders[$name] = $statements;
}

            
afterAction() public method

Defined in: yii\base\ActionFilter::afterAction()

This method is invoked right after an action is executed.

You may override this method to do some postprocessing for the action.

public mixed afterAction ( $action, $result )
$action yii\base\Action

The action just executed.

$result mixed

The action execution result

return mixed

The processed action result.

                public function afterAction($action, $result)
{
    return $result;
}

            
afterFilter() public method
public void afterFilter ( $event )
$event yii\base\ActionEvent

                public function afterFilter($event)
{
    $event->result = $this->afterAction($event->action, $event->result);
    $this->owner->off(Controller::EVENT_AFTER_ACTION, [$this, 'afterFilter']);
}

            
afterRestoreResponse() public method (available since version 2.0.11)

This method is invoked right after the response restoring is finished (but before the response is sent).

You may override this method to do last-minute preparation before the response is sent.

public void afterRestoreResponse ( $data )
$data array|null

An array of an additional data stored in a cache entry or null.

                public function afterRestoreResponse($data)
{
}

            
attach() public method

Defined in: yii\base\ActionFilter::attach()

Attaches the behavior object to the component.

The default implementation will set the $owner property and attach event handlers as declared in events(). Make sure you call the parent implementation if you override this method.

public void attach ( $owner )
$owner yii\base\Component

The component that this behavior is to be attached to.

                public function attach($owner)
{
    $this->owner = $owner;
    $owner->on(Controller::EVENT_BEFORE_ACTION, [$this, 'beforeFilter']);
}

            
beforeAction() public method

This method is invoked right before an action is to be executed (after all possible filters.) You may override this method to do last-minute preparation for the action.

public boolean beforeAction ( $action )
$action yii\base\Action

The action to be executed.

return boolean

Whether the action should continue to be executed.

                public function beforeAction($action)
{
    if (!$this->enabled) {
        return true;
    }
    $this->cache = Instance::ensure($this->cache, 'yii\caching\CacheInterface');
    if (is_array($this->dependency)) {
        $this->dependency = Yii::createObject($this->dependency);
    }
    $response = Yii::$app->getResponse();
    $data = $this->cache->get($this->calculateCacheKey());
    if (!is_array($data) || !isset($data['cacheVersion']) || $data['cacheVersion'] !== static::PAGE_CACHE_VERSION) {
        $this->view->pushDynamicContent($this);
        ob_start();
        ob_implicit_flush(false);
        $response->on(Response::EVENT_AFTER_SEND, [$this, 'cacheResponse']);
        Yii::debug('Valid page content is not found in the cache.', __METHOD__);
        return true;
    }
    $this->restoreResponse($response, $data);
    Yii::debug('Valid page content is found in the cache.', __METHOD__);
    return false;
}

            
beforeCacheResponse() public method (available since version 2.0.11)

This method is invoked right before the response caching is to be started.

You may override this method to cancel caching by returning false or store an additional data in a cache entry by returning an array instead of true.

public boolean|array beforeCacheResponse ( )
return boolean|array

Whether to cache or not, return an array instead of true to store an additional data.

                public function beforeCacheResponse()
{
    return true;
}

            
beforeFilter() public method
public void beforeFilter ( $event )
$event yii\base\ActionEvent

                public function beforeFilter($event)
{
    if (!$this->isActive($event->action)) {
        return;
    }
    $event->isValid = $this->beforeAction($event->action);
    if ($event->isValid) {
        // call afterFilter only if beforeFilter succeeds
        // beforeFilter and afterFilter should be properly nested
        $this->owner->on(Controller::EVENT_AFTER_ACTION, [$this, 'afterFilter'], null, false);
    } else {
        $event->handled = true;
    }
}

            
cacheResponse() public method (available since version 2.0.3)

Caches response properties.

public void cacheResponse ( )

                public function cacheResponse()
{
    $this->view->popDynamicContent();
    $beforeCacheResponseResult = $this->beforeCacheResponse();
    if ($beforeCacheResponseResult === false) {
        echo $this->updateDynamicContent(ob_get_clean(), $this->getDynamicPlaceholders());
        return;
    }
    $response = Yii::$app->getResponse();
    $response->off(Response::EVENT_AFTER_SEND, [$this, 'cacheResponse']);
    $data = [
        'cacheVersion' => static::PAGE_CACHE_VERSION,
        'cacheData' => is_array($beforeCacheResponseResult) ? $beforeCacheResponseResult : null,
        'content' => ob_get_clean(),
    ];
    if ($data['content'] === false || $data['content'] === '') {
        return;
    }
    $data['dynamicPlaceholders'] = $this->getDynamicPlaceholders();
    foreach (['format', 'version', 'statusCode', 'statusText'] as $name) {
        $data[$name] = $response->{$name};
    }
    $this->insertResponseHeaderCollectionIntoData($response, $data);
    $this->insertResponseCookieCollectionIntoData($response, $data);
    $this->cache->set($this->calculateCacheKey(), $data, $this->duration, $this->dependency);
    $data['content'] = $this->updateDynamicContent($data['content'], $this->getDynamicPlaceholders());
    echo $data['content'];
}

            
calculateCacheKey() protected method (available since version 2.0.3)

protected array calculateCacheKey ( )
return array

The key used to cache response properties.

                protected function calculateCacheKey()
{
    $key = [__CLASS__];
    if ($this->varyByRoute) {
        $key[] = Yii::$app->requestedRoute;
    }
    return array_merge($key, (array)$this->variations);
}

            
canGetProperty() public method

Defined in: yii\base\BaseObject::canGetProperty()

Returns a value indicating whether a property can be read.

A property is readable if:

  • the class has a getter method associated with the specified name (in this case, property name is case-insensitive);
  • the class has a member variable with the specified name (when $checkVars is true);

See also canSetProperty().

public boolean canGetProperty ( $name, $checkVars true )
$name string

The property name

$checkVars boolean

Whether to treat member variables as properties

return boolean

Whether the property can be read

                public function canGetProperty($name, $checkVars = true)
{
    return method_exists($this, 'get' . $name) || $checkVars && property_exists($this, $name);
}

            
canSetProperty() public method

Defined in: yii\base\BaseObject::canSetProperty()

Returns a value indicating whether a property can be set.

A property is writable if:

  • the class has a setter method associated with the specified name (in this case, property name is case-insensitive);
  • the class has a member variable with the specified name (when $checkVars is true);

See also canGetProperty().

public boolean canSetProperty ( $name, $checkVars true )
$name string

The property name

$checkVars boolean

Whether to treat member variables as properties

return boolean

Whether the property can be written

                public function canSetProperty($name, $checkVars = true)
{
    return method_exists($this, 'set' . $name) || $checkVars && property_exists($this, $name);
}

            
className() public static method
Deprecated since 2.0.14. On PHP >=5.5, use ::class instead.

Defined in: yii\base\BaseObject::className()

Returns the fully qualified name of this class.

public static string className ( )
return string

The fully qualified name of this class.

                public static function className()
{
    return get_called_class();
}

            
detach() public method

Defined in: yii\base\ActionFilter::detach()

Detaches the behavior object from the component.

The default implementation will unset the $owner property and detach event handlers declared in events(). Make sure you call the parent implementation if you override this method.

public void detach ( )

                public function detach()
{
    if ($this->owner) {
        $this->owner->off(Controller::EVENT_BEFORE_ACTION, [$this, 'beforeFilter']);
        $this->owner->off(Controller::EVENT_AFTER_ACTION, [$this, 'afterFilter']);
        $this->owner = null;
    }
}

            
events() public method

Defined in: yii\base\Behavior::events()

Declares event handlers for the $owner's events.

Child classes may override this method to declare what PHP callbacks should be attached to the events of the $owner component.

The callbacks will be attached to the $owner's events when the behavior is attached to the owner; and they will be detached from the events when the behavior is detached from the component.

The callbacks can be any of the following:

  • method in this behavior: 'handleClick', equivalent to [$this, 'handleClick']
  • object method: [$object, 'handleClick']
  • static method: ['Page', 'handleClick']
  • anonymous function: function ($event) { ... }

The following is an example:

[
    Model::EVENT_BEFORE_VALIDATE => 'myBeforeValidate',
    Model::EVENT_AFTER_VALIDATE => 'myAfterValidate',
]
public array events ( )
return array

Events (array keys) and the corresponding event handler methods (array values).

                public function events()
{
    return [];
}

            
getActionId() protected method (available since version 2.0.7)

Defined in: yii\base\ActionFilter::getActionId()

Returns an action ID by converting yii\base\Action::$uniqueId into an ID relative to the module.

protected string getActionId ( $action )
$action yii\base\Action

                protected function getActionId($action)
{
    if ($this->owner instanceof Module) {
        $mid = $this->owner->getUniqueId();
        $id = $action->getUniqueId();
        if ($mid !== '' && strpos($id, $mid) === 0) {
            $id = substr($id, strlen($mid) + 1);
        }
    } else {
        $id = $action->id;
    }
    return $id;
}

            
getDynamicPlaceholders() public method

Defined in: yii\base\DynamicContentAwareTrait::getDynamicPlaceholders()

Returns a list of placeholders for dynamic content. This method is used internally to implement the content caching feature.

public array getDynamicPlaceholders ( )
return array

A list of placeholders.

                public function getDynamicPlaceholders()
{
    return $this->_dynamicPlaceholders;
}

            
getView() public method

public void getView ( )

                public function getView()
{
    return $this->view;
}

            
hasMethod() public method

Defined in: yii\base\BaseObject::hasMethod()

Returns a value indicating whether a method is defined.

The default implementation is a call to php function method_exists(). You may override this method when you implemented the php magic method __call().

public boolean hasMethod ( $name )
$name string

The method name

return boolean

Whether the method is defined

                public function hasMethod($name)
{
    return method_exists($this, $name);
}

            
hasProperty() public method

Defined in: yii\base\BaseObject::hasProperty()

Returns a value indicating whether a property is defined.

A property is defined if:

  • the class has a getter or setter method associated with the specified name (in this case, property name is case-insensitive);
  • the class has a member variable with the specified name (when $checkVars is true);

See also:

public boolean hasProperty ( $name, $checkVars true )
$name string

The property name

$checkVars boolean

Whether to treat member variables as properties

return boolean

Whether the property is defined

                public function hasProperty($name, $checkVars = true)
{
    return $this->canGetProperty($name, $checkVars) || $this->canSetProperty($name, false);
}

            
init() public method

Initializes the object.

This method is invoked at the end of the constructor after the object is initialized with the given configuration.

public void init ( )

                public function init()
{
    parent::init();
    if ($this->view === null) {
        $this->view = Yii::$app->getView();
    }
}

            
isActive() protected method

Defined in: yii\base\ActionFilter::isActive()

Returns a value indicating whether the filter is active for the given action.

protected boolean isActive ( $action )
$action yii\base\Action

The action being filtered

return boolean

Whether the filter is active for the given action.

                protected function isActive($action)
{
    $id = $this->getActionId($action);
    if (empty($this->only)) {
        $onlyMatch = true;
    } else {
        $onlyMatch = false;
        foreach ($this->only as $pattern) {
            if (StringHelper::matchWildcard($pattern, $id)) {
                $onlyMatch = true;
                break;
            }
        }
    }
    $exceptMatch = false;
    foreach ($this->except as $pattern) {
        if (StringHelper::matchWildcard($pattern, $id)) {
            $exceptMatch = true;
            break;
        }
    }
    return !$exceptMatch && $onlyMatch;
}

            
restoreResponse() protected method (available since version 2.0.3)

Restores response properties from the given data.

protected void restoreResponse ( $response, $data )
$response yii\web\Response

The response to be restored.

$data array

The response property data.

                protected function restoreResponse($response, $data)
{
    foreach (['format', 'version', 'statusCode', 'statusText', 'content'] as $name) {
        $response->{$name} = $data[$name];
    }
    foreach (['headers', 'cookies'] as $name) {
        if (isset($data[$name]) && is_array($data[$name])) {
            $response->{$name}->fromArray(array_merge($data[$name], $response->{$name}->toArray()));
        }
    }
    if (!empty($data['dynamicPlaceholders']) && is_array($data['dynamicPlaceholders'])) {
        $response->content = $this->updateDynamicContent($response->content, $data['dynamicPlaceholders'], true);
    }
    $this->afterRestoreResponse(isset($data['cacheData']) ? $data['cacheData'] : null);
}

            
setDynamicPlaceholders() public method

Defined in: yii\base\DynamicContentAwareTrait::setDynamicPlaceholders()

Sets a list of placeholders for dynamic content. This method is used internally to implement the content caching feature.

public void setDynamicPlaceholders ( $placeholders )
$placeholders array

A list of placeholders.

                public function setDynamicPlaceholders($placeholders)
{
    $this->_dynamicPlaceholders = $placeholders;
}

            
updateDynamicContent() protected method

Defined in: yii\base\DynamicContentAwareTrait::updateDynamicContent()

Replaces placeholders in $content with results of evaluated dynamic statements.

protected string updateDynamicContent ( $content, $placeholders, $isRestoredFromCache false )
$content string

Content to be parsed.

$placeholders string[]

Placeholders and their values.

$isRestoredFromCache boolean

Whether content is going to be restored from cache.

return string

Final content.

                protected function updateDynamicContent($content, $placeholders, $isRestoredFromCache = false)
{
    if (empty($placeholders) || !is_array($placeholders)) {
        return $content;
    }
    if (count($this->getView()->getDynamicContents()) === 0) {
        // outermost cache: replace placeholder with dynamic content
        foreach ($placeholders as $name => $statements) {
            $placeholders[$name] = $this->getView()->evaluateDynamicContent($statements);
        }
        $content = strtr($content, $placeholders);
    }
    if ($isRestoredFromCache) {
        $view = $this->getView();
        foreach ($placeholders as $name => $statements) {
            $view->addDynamicPlaceholder($name, $statements);
        }
    }
    return $content;
}