RendererInterface.php
Same filename in other branches
Namespace
Drupal\Core\RenderFile
-
core/
lib/ Drupal/ Core/ Render/ RendererInterface.php
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<?php
namespace Drupal\Core\Render;
/**
* Defines an interface for turning a render array into a string.
*/
interface RendererInterface {
/**
* Renders final HTML given a structured array tree.
*
* Calls ::render() in such a way that placeholders are replaced.
*
* Should therefore only be used in occasions where the final rendering is
* happening, just before sending a Response:
* - system internals that are responsible for rendering the final HTML
* - render arrays for non-HTML responses, such as feeds
*
* (Cannot be executed within another render context.)
*
* @param array $elements
* The structured array describing the data to be rendered.
*
* @return \Drupal\Component\Render\MarkupInterface
* The rendered HTML.
*
* @throws \LogicException
* When called from inside another renderRoot() call.
*
* @see \Drupal\Core\Render\RendererInterface::render()
*/
public function renderRoot(&$elements);
/**
* Renders final HTML in situations where no assets are needed.
*
* Calls ::render() in such a way that placeholders are replaced.
*
* Useful for instance when rendering the values of tokens or emails, which
* need a render array being turned into a string, but do not need any of the
* bubbleable metadata (the attached assets and cache tags).
*
* Some of these are a relatively common use case and happen *within* a
* ::renderRoot() call, but that is generally highly problematic (and hence an
* exception is thrown when a ::renderRoot() call happens within another
* ::renderRoot() call). However, in this case, we only care about the output,
* not about the bubbling. Hence this uses a separate render context, to not
* affect the parent ::renderRoot() call.
*
* (Can be executed within another render context: it runs in isolation.)
*
* @param array $elements
* The structured array describing the data to be rendered.
*
* @return \Drupal\Component\Render\MarkupInterface
* The rendered HTML.
*
* @see \Drupal\Core\Render\RendererInterface::renderRoot()
* @see \Drupal\Core\Render\RendererInterface::render()
*/
public function renderInIsolation(&$elements);
/**
* @deprecated in drupal:10.3.0 and is removed from drupal:12.0.0. Use
* \Drupal\Core\Render\RendererInterface::renderInIsolation() instead.
*
* @see https://www.drupal.org/node/3407994
*/
public function renderPlain(&$elements);
/**
* Renders final HTML for a placeholder.
*
* Renders the placeholder in isolation.
*
* @param string $placeholder
* An attached placeholder to render. (This must be a key of one of the
* values of $elements['#attached']['placeholders'].)
* @param array $elements
* The structured array describing the data to be rendered.
*
* @return array
* The updated $elements.
*
* @see \Drupal\Core\Render\RendererInterface::render()
*/
public function renderPlaceholder($placeholder, array $elements);
/**
* Renders HTML given a structured array tree.
*
* Renderable arrays have two kinds of key/value pairs: properties and
* children. Properties have keys starting with '#' and their values influence
* how the array will be rendered. Children are all elements whose keys do not
* start with a '#'. Their values should be renderable arrays themselves,
* which will be rendered during the rendering of the parent array. The markup
* provided by the children is typically inserted into the markup generated by
* the parent array.
*
* An important aspect of rendering is caching the result, when appropriate.
* Because the HTML of a rendered item includes all of the HTML of the
* rendered children, caching it requires certain information to bubble up
* from child elements to their parents:
* - Cache contexts, so that the render cache is varied by every context that
* affects the rendered HTML. Because cache contexts affect the cache ID,
* and therefore must be resolved for cache hits as well as misses, it is
* up to the implementation of this interface to decide how to implement
* the caching of items whose children specify cache contexts not directly
* specified by the parent. \Drupal\Core\Render\Renderer implements this
* with a lazy two-tier caching strategy. Alternate strategies could be to
* not cache such parents at all or to cache them with the child elements
* replaced by placeholder tokens that are dynamically rendered after cache
* retrieval.
* - Cache tags, so that cached renderings are invalidated when site content
* or configuration that can affect that rendering changes.
* - Placeholders, with associated self-contained placeholder render arrays,
* for executing code to handle dynamic requirements that cannot be cached.
* A render context (\Drupal\Core\Render\RenderContext) can be used to perform
* bubbling; it is a stack of \Drupal\Core\Render\BubbleableMetadata objects.
*
* Additionally, whether retrieving from cache or not, it is important to
* know all of the assets (CSS and JavaScript) required by the rendered HTML,
* and this must also bubble from child to parent. Therefore,
* \Drupal\Core\Render\BubbleableMetadata includes that data as well.
*
* The process of rendering an element is recursive unless the element defines
* an implemented theme hook in #theme. During each call to
* Renderer::render(), the outermost renderable array (also known as an
* "element") is processed using the following steps:
* - If this element has already been printed (#printed = TRUE) or the user
* does not have access to it (#access = FALSE), then an empty string is
* returned.
* - If no render context is set yet, an exception is thrown. Otherwise,
* an empty \Drupal\Core\Render\BubbleableMetadata is pushed onto the
* render context.
* - If this element has #cache defined then the cached markup for this
* element will be returned if it exists in Renderer::render()'s cache. To
* use Renderer::render() caching, set the element's #cache property to an
* associative array with one or several of the following keys:
* - 'keys': An array of one or more keys that identify the element. If
* 'keys' is set, the cache ID is created automatically from these keys.
* - 'contexts': An array of one or more cache context IDs. These are
* converted to a final value depending on the request. (For instance,
* 'user' is mapped to the current user's ID.)
* - 'max-age': A time in seconds. Zero seconds means it is not cacheable.
* \Drupal\Core\Cache\Cache::PERMANENT means it is cacheable forever.
* - 'bin': Specify a cache bin to cache the element in. Default is
* 'default'.
* When there is a render cache hit, there is no rendering work left to be
* done, so the stack must be updated. The empty (and topmost) frame that
* was just pushed onto the stack is updated with all bubbleable rendering
* metadata from the element retrieved from render cache. Then, this stack
* frame is bubbled: the two topmost frames are popped from the stack,
* they are merged, and the result is pushed back onto the stack.
* However, also in case of a cache miss we have to do something. Note
* that a Renderer renders top-down, which means that we try to render a
* parent first, and we try to avoid the work of rendering the children by
* using the render cache. Though in this case, we are dealing with a
* cache miss. So a Renderer traverses down the tree, rendering all
* children. In doing so, the render stack is updated with the bubbleable
* metadata of the children. That means that once the children are
* rendered, we can render cache this element. But the cache ID may have
* *changed* at that point, because the children's cache contexts have
* been bubbled!
* It is for that case that we must store the current (pre-bubbling) cache
* ID, so that we can compare it with the new (post-bubbling) cache ID
* when writing to the cache. We store the current cache ID in
* $pre_bubbling_cid.
* - If this element has #type defined and the default attributes for this
* element have not already been merged in (#defaults_loaded = TRUE) then
* the defaults for this type of element, defined by an element plugin,
* are merged into the array. #defaults_loaded is set by functions that
* process render arrays and call the element info service before passing
* the array to Renderer::render(), such as form_builder() in the Form
* API.
* - If this element has #create_placeholder set to TRUE, and it has a
* #lazy_builder callback, then the element is replaced with another
* element that has only two properties: #markup and #attached. #markup
* will contain placeholder markup, and #attached contains the placeholder
* metadata, that will be used for replacing this placeholder. That
* metadata contains a very compact render array (containing only
* #lazy_builder and #cache) that will be rendered to replace the
* placeholder with its final markup. This means that when the
* #lazy_builder callback is called, it received a render array to add to
* that only contains #cache.
* - If this element has a #lazy_builder or an array of #pre_render
* functions defined, they are called sequentially to modify the element
* before rendering. #lazy_builder is preferred, since it allows for
* placeholdering (see previous step), but #pre_render is still supported.
* Both have their use case: #lazy_builder is for building a render array,
* #pre_render is for decorating an existing render array.
* After the #lazy_builder function is called, #lazy_builder is removed,
* and #built is set to TRUE.
* After the #lazy_builder and all #pre_render functions have been called,
* #printed is checked a second time in case a #lazy_builder or
* #pre_render function flags the element as printed. If #printed is set,
* we return early and hence no rendering work is left to be done,
* similarly to a render cache hit. Once again, the empty (and topmost)
* frame that was just pushed onto the stack is updated with all
* bubbleable rendering metadata from the element whose #printed = TRUE.
* Then, this stack frame is bubbled: the two topmost frames are popped
* from the stack, they are merged, and the result is pushed back onto the
* stack.
* - The child elements of this element are sorted by weight using uasort()
* in \Drupal\Core\Render\Element::children(). Since this is expensive,
* when passing already sorted elements to Renderer::render(), for example
* from a database query, set $elements['#sorted'] = TRUE to avoid sorting
* them a second time.
* - The main render phase to produce #children for this element takes
* place:
* - If this element has #theme defined and #theme is an implemented theme
* hook/suggestion then ThemeManagerInterface::render() is called and
* must render both the element and its children. If #render_children is
* set, ThemeManagerInterface::render() will not be called.
* #render_children is usually only set internally by
* ThemeManagerInterface::render() so that we can avoid the situation
* where Renderer::render() called from within a theme preprocess
* function creates an infinite loop.
* - If this element does not have a defined #theme, or the defined #theme
* hook is not implemented, or #render_children is set, then
* Renderer::render() is called recursively on each of the child
* elements of this element, and the result of each is concatenated onto
* #children. This is skipped if #children is not empty at this point.
* - Once #children has been rendered for this element, if #theme is not
* implemented and #markup is set for this element, #markup will be
* prepended to #children.
* - If this element has #states defined then JavaScript state information
* is added to this element's #attached attribute by
* \Drupal\Core\Form\FormHelper::processStates().
* - If this element has #attached defined then any required libraries,
* JavaScript, CSS, or other custom data are added to the current page by
* \Drupal\Core\Render\AttachmentsResponseProcessorInterface::processAttachments().
* - If this element has an array of #theme_wrappers defined and
* #render_children is not set, #children is then re-rendered by passing
* the element in its current state to ThemeManagerInterface::render()
* successively for each item in #theme_wrappers. Since #theme and
* #theme_wrappers hooks often define variables with the same names it is
* possible to explicitly override each attribute passed to each
* #theme_wrappers hook by setting the hook name as the key and an array
* of overrides as the value in #theme_wrappers array.
* For example, if we have a render element as follows:
* @code
* [
* '#theme' => 'image',
* '#attributes' => ['class' => ['foo']],
* '#theme_wrappers' => ['container'],
* ];
* @endcode
* and we need to pass the class 'bar' as an attribute for 'container', we
* can rewrite our element thus:
* @code
* [
* '#theme' => 'image',
* '#attributes' => ['class' => ['foo']],
* '#theme_wrappers' => [
* 'container' => [
* '#attributes' => ['class' => ['bar']],
* ],
* ],
* ];
* @endcode
* - If this element has an array of #post_render functions defined, they
* are called sequentially to modify the rendered #children. Unlike
* #pre_render functions, #post_render functions are passed both the
* rendered #children attribute as a string and the element itself.
* - If this element has #prefix and/or #suffix defined, they are
* concatenated to #children.
* - The rendering of this element is now complete. The next step will be
* render caching. So this is the perfect time to update the stack. At
* this point, children of this element (if any), have been rendered also,
* and if there were any, their bubbleable rendering metadata will have
* been bubbled up into the stack frame for the element that is currently
* being rendered. The render cache item for this element must contain the
* bubbleable rendering metadata for this element and all of its children.
* However, right now, the topmost stack frame (the one for this element)
* currently only contains the metadata for the children. Therefore, the
* topmost stack frame is updated with this element's metadata, and then
* the element's metadata is replaced with the metadata in the topmost
* stack frame. This element now contains all bubbleable rendering
* metadata for this element and all its children, so it's now ready for
* render caching.
* - If this element has #cache defined, the rendered output of this element
* is saved to Renderer::render()'s internal cache. This includes the
* changes made by #post_render.
* At the same time, if $pre_bubbling_cid is set, it is compared to the
* calculated cache ID. If they are different, then a redirecting cache
* item is created, containing the #cache metadata of the current element,
* and written to cache using the value of $pre_bubbling_cid as the cache
* ID. This ensures the pre-bubbling ("wrong") cache ID redirects to the
* post-bubbling ("right") cache ID.
* - If this element also has #cache_properties defined, all the array items
* matching the specified property names will be cached along with the
* element markup. If properties include children names, the system
* assumes only children's individual markup is relevant and ignores the
* parent markup. This approach is normally not needed and should be
* adopted only when dealing with very advanced use cases.
* - If this element has attached placeholders ([#attached][placeholders]),
* or any of its children has (which we would know thanks to the stack
* having been updated just before the render caching step), its
* placeholder element containing a #lazy_builder function is rendered in
* isolation. The resulting markup is used to replace the placeholder, and
* any bubbleable metadata is merged.
* Placeholders must be unique, to guarantee that for instance, samples of
* placeholders are not replaced as well.
* - Just before finishing the rendering of this element, this element's
* stack frame (the topmost one) is bubbled: the two topmost frames are
* popped from the stack, they are merged and the result is pushed back
* onto the stack.
* So if for instance this element was a child element, then a new frame
* was pushed onto the stack element at the beginning of rendering this
* element, it was updated when the rendering was completed, and now we
* merge it with the frame for the parent, so that the parent now has the
* bubbleable rendering metadata for its child.
* - #printed is set to TRUE for this element to ensure that it is only
* rendered once.
* - The final value of #children for this element is returned as the
* rendered output.
*
* @param array $elements
* The structured array describing the data to be rendered.
* @param bool $is_root_call
* (Internal use only.) Whether this is a recursive call or not. See
* ::renderRoot().
*
* @return \Drupal\Component\Render\MarkupInterface
* The rendered HTML.
*
* @throws \LogicException
* When called outside of a render context (i.e. outside of a renderRoot(),
* renderInIsolation() or executeInRenderContext() call).
* @throws \Exception
* If a #pre_render callback throws an exception, it is caught to mark the
* renderer as no longer being in a root render call, if any. Then the
* exception is rethrown.
*
* @see \Drupal\Core\Render\ElementInfoManagerInterface::getInfo()
* @see \Drupal\Core\Theme\ThemeManagerInterface::render()
* @see \Drupal\Core\Form\FormHelper::processStates()
* @see \Drupal\Core\Render\AttachmentsResponseProcessorInterface::processAttachments()
* @see \Drupal\Core\Render\RendererInterface::renderRoot()
*/
public function render(&$elements, $is_root_call = FALSE);
/**
* Checks whether a render context is active.
*
* This is useful only in very specific situations to determine whether the
* system is already capable of collecting bubbleable metadata. Normally it
* should not be necessary to be concerned about this.
*
* @return bool
* TRUE if the renderer has a render context active, FALSE otherwise.
*/
public function hasRenderContext();
/**
* Executes a callable within a render context.
*
* Only for very advanced use cases. Prefer using ::renderRoot() and
* ::renderInIsolation() instead.
*
* All rendering must happen within a render context. Within a render context,
* all bubbleable metadata is bubbled and hence tracked. Outside of a render
* context, it would be lost. This could lead to missing assets, incorrect
* cache variations (and thus security issues), insufficient cache
* invalidations, and so on.
*
* Any and all rendering must therefore happen within a render context, and it
* is this method that provides that.
*
* @param \Drupal\Core\Render\RenderContext $context
* The render context to execute the callable within.
* @param callable $callable
* The callable to execute.
*
* @return mixed
* The callable's return value.
*
* @throws \LogicException
* In case bubbling has failed, can only happen in case of broken code.
*
* @see \Drupal\Core\Render\RenderContext
* @see \Drupal\Core\Render\BubbleableMetadata
*/
public function executeInRenderContext(RenderContext $context, callable $callable);
/**
* Merges the bubbleable rendering metadata o/t 2nd render array with the 1st.
*
* @param array $a
* A render array.
* @param array $b
* A render array.
*
* @return array
* The first render array, modified to also contain the bubbleable rendering
* metadata of the second render array.
*
* @see \Drupal\Core\Render\BubbleableMetadata
*/
public function mergeBubbleableMetadata(array $a, array $b);
/**
* Adds a dependency on an object: merges its cacheability metadata.
*
* For instance, when a render array depends on some configuration, an entity,
* or an access result, we must make sure their cacheability metadata is
* present on the render array. This method makes doing that simple.
*
* @param array &$elements
* The render array to update.
* @param \Drupal\Core\Cache\CacheableDependencyInterface|mixed $dependency
* The dependency. If the object implements CacheableDependencyInterface,
* then its cacheability metadata will be used. Otherwise, the passed in
* object must be assumed to be uncacheable, so max-age 0 is set.
*
* @see \Drupal\Core\Cache\CacheableMetadata::createFromObject()
*/
public function addCacheableDependency(array &$elements, $dependency);
}
Interfaces
Title | Deprecated | Summary |
---|---|---|
RendererInterface | Defines an interface for turning a render array into a string. |
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