Component Model
***************

.[perex]
An important concept in Nette is the component. We insert [visual interactive components |application:components] into pages, forms or all their elements are also components. There are two basic classes from which all these components inherit, are part of the `nette/component-model` package and are responsible for creating the component tree hierarchy.


Component
=========
[api:Nette\ComponentModel\Component] is the common ancestor of all components. It contains the `getName()` method returning the name of the component and the `getParent()` method returning its parent. Both can be set with the `setParent()` method - the first parameter is the parent and the second is the component name.


lookup(string $type): ?Component .[method]
------------------------------------------
Searches up the hierarchy for an object of the desired class or interface. For example, `$component->lookup(Nette\Application\UI\Presenter::class)` returns presenter if the component is connected to it, despite several levels.


lookupPath(string $type): ?string .[method]
-------------------------------------------
Returns the so-called path, which is a string formed by concatenating the names of all components on the path between the current component and the component being searched for. So, for example, `$component->lookupPath(Nette\Application\UI\Presenter::class)` returns the unique identifier of the component relative to the presenter.


Container
=========
[api:Nette\ComponentModel\Container] is the parent component, i.e. the component containing the children and thus forming the tree structure. It has methods for easily adding, retrieving and removing components. It is the ancestor of, for example, the form or classes `Control` and `Presenter`.


getComponent(string $name): ?Component .[method]
------------------------------------------------
Returns a component. Attempt to call undefined child causes invoking of factory [createComponent($name)|api:Nette\ComponentModel\Container::createComponent()]. Method `createComponent($name)` invokes method `createComponent<component name>` in current component and it passes name of the component as a parameter. Created component is then passed to current component as its child. We call theese component factories, they can be implemented in classes inherited from `Container`.


getComponents(): array .[method]
--------------------------------
Returns direct descendants as an array. The keys contain the names of these components. Note: in version 3.0.x, the method returned an iterator instead of an array, and its first parameter specified whether to iterate through the components in depth, and the second represented a type filter. These parameters are deprecated.


getComponentTree(): array .[method]{data-version:3.1.0}
-------------------------------------------------------
Returns the entire hierarchy of components, including all nested child components as indexed array. The search goes in depth first.


Monitoring of Ancestors
=======================

The Nette component model allows for very dynamic tree work (we can remove, move, add components), so it would be a mistake to rely on the fact that after creating a component, the parent, parent's parent, etc. are known immediately (in the constructor). Usually the parent is not known at all when the component is created.

How to find out when a component has been added to the presenter tree? Keeping track of the parent change is not enough, because the parent of the parent could have been attached to the presenter, for example. The [monitor($type, $attached, $detached) |api:Nette\ComponentModel\Component::monitor()] method can help. Each component can monitor any number of classes and interfaces. Connection or disconnection is announced by calling the callbacks `$attached` and `$detached`, respectively, and passing the object of the monitored class.

An example: Class `UploadControl`, representing form element for uploading files in Nette Forms, has to set form's attribute `enctype` to value `multipart/form-data`. But in the time of the creation of the object it does not have to be attached to any form. When to modify the form? The solution is simple - we create a request for monitoring in the constructor:

```php
class UploadControl extends Nette\Forms\Controls\BaseControl
{
	public function __construct($label)
	{
		$this->monitor(Nette\Forms\Form::class, function ($form): void {
			$form->setHtmlAttribute('enctype', 'multipart/form-data');
		});
		// ...
	}

	// ...
}
```

and when the form is available, the callback is called. (Previously, the common methods `attached` and `detached` were used instead.)


{{leftbar: nette:@menu-topics}}