com.vaadin.flow.component

Class Component

java.lang.Object

com.vaadin.flow.component.Component

All Implemented Interfaces:

AttachNotifier, DetachNotifier, HasElement, Serializable

Direct Known Subclasses:

AbstractField, AbstractTemplate, Composite, Html, HtmlComponent, InternalServerError, RouteNotFoundError, RouterLink, Text, UI, WebComponentWrapper

public abstract class Component
extends Object
implements HasElement, AttachNotifier, DetachNotifier

A Component is a higher level abstraction of an Element or a hierarchy of Elements.

A component must have exactly one root element which is created based on the Tag annotation of the sub class (or in special cases set using the constructor Component(Element) or using setElement(Component, Element) before the element is attached to a parent). The root element cannot be changed once it has been set.

Since:

1.0

Author:

Vaadin Ltd

See Also:

Serialized Form

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Component() Creates a component instance with an element created based on the Tag annotation of the sub class.
protected	Component(Element element) Creates a component instance based on the given element.

Method Summary

Modifier and Type	Method and Description
protected <T extends ComponentEvent<?>> Registration	addListener(Class<T> eventType, ComponentEventListener<T> listener) Adds a listener for an event of the given type.
protected void	fireEvent(ComponentEvent<?> componentEvent) Dispatches the event to all listeners registered for the event type.
static <T extends Component> T	from(Element element, Class<T> componentType) Creates a new component instance using the given element.
protected <T> T	get(PropertyDescriptor<?,T> descriptor) Gets the value of the given component property.
Stream<Component>	getChildren() Gets the child components of this component.
Element	getElement() Gets the root element of this component.
protected ComponentEventBus	getEventBus() Gets the event bus for this component.
Optional<String>	getId() Gets the id of the root element of this component.
protected Locale	getLocale() Gets the locale for this component.
Optional<Component>	getParent() Gets the parent component of this component.
String	getTranslation(String key, Locale locale, Object... params) Get the translation for key with given locale.
String	getTranslation(String key, Object... params) Get the translation for the component locale.
Optional<UI>	getUI() Gets the UI this component is attached to.
protected boolean	hasListener(Class<? extends ComponentEvent> eventType) Checks if there is at least one listener registered for the given event type for this component.
protected boolean	isTemplateMapped() Gets whether this component was attached as part of a PolymerTemplate (by being mapped by an Id annotation), or if it was created directly.
boolean	isVisible() Gets the component visibility value.
protected void	onAttach(AttachEvent attachEvent) Called when the component is attached to a UI.
protected void	onDetach(DetachEvent detachEvent) Called when the component is detached from a UI.
void	onEnabledStateChanged(boolean enabled) Handle component enable state when the enabled state changes.
protected <T> void	set(PropertyDescriptor<T,?> descriptor, T value) Sets the value of the given component property.
protected static void	setElement(Component component, Element element) Initializes the root element of a component.
void	setId(String id) Sets the id of the root element of this component.
void	setVisible(boolean visible) Sets the component visibility value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface com.vaadin.flow.component.AttachNotifier

addAttachListener

Methods inherited from interface com.vaadin.flow.component.DetachNotifier

addDetachListener

Constructor Detail

Component

protected Component()

Creates a component instance with an element created based on the Tag annotation of the sub class.

If this is invoked through from(Element, Class) or Element.as(Class), uses the element defined in those methods instead of creating a new element.

Component

protected Component(Element element)

Creates a component instance based on the given element.

For nearly all cases you want to pass an element reference but it is possible to pass null to this method. If you pass null you must ensure that the element is initialized using setElement(Component, Element) before getElement() is used.

Parameters:

element - the root element for the component

Method Detail

getElement

public Element getElement()

Gets the root element of this component.

Each component must have exactly one root element. When the component is attached to a parent component, this element is attached to the parent component's element hierarchy.

Specified by:

getElement in interface HasElement

Returns:

the root element of this component

setElement

protected static void setElement(Component component,
                                 Element element)

Initializes the root element of a component.

Each component must have a root element and it must be set before the component is attached to a parent. The root element of a component cannot be changed once it has been set.

Typically you do not want to call this method but define the element through Component(Element) instead.

Parameters:

component - the component to set the root element to

element - the root element of the component

getParent

public Optional<Component> getParent()

Gets the parent component of this component.

A component can only have one parent.

Returns:

an optional parent component, or an empty optional if the component is not attached to a parent

getChildren

public Stream<Component> getChildren()

Gets the child components of this component.

The default implementation finds child components by traversing each child Element tree.

If the component is injected to a PolymerTemplate using the @Id annotation the getChildren method will only return children added from the server side and will not return any children declared in the template file.

Returns:

the child components of this component

See Also:

Id

getEventBus

protected ComponentEventBus getEventBus()

Gets the event bus for this component.

This method will create the event bus if it has not yet been created.

Returns:

the event bus for this component

addListener

protected <T extends ComponentEvent<?>> Registration addListener(Class<T> eventType,
                                                                 ComponentEventListener<T> listener)

Adds a listener for an event of the given type.

Type Parameters:

T - the component event type

Parameters:

eventType - the component event type, not null

listener - the listener to add, not null

Returns:

a handle that can be used for removing the listener

hasListener

protected boolean hasListener(Class<? extends ComponentEvent> eventType)

Checks if there is at least one listener registered for the given event type for this component.

Parameters:

eventType - the component event type

Returns:

true if at least one listener is registered, false otherwise

fireEvent

protected void fireEvent(ComponentEvent<?> componentEvent)

Dispatches the event to all listeners registered for the event type.

Parameters:

componentEvent - the event to fire

See Also:

ComponentUtil.fireEvent(Component, ComponentEvent)

getUI

public Optional<UI> getUI()

Gets the UI this component is attached to.

Returns:

an optional UI component, or an empty optional if this component is not attached to a UI

setId

public void setId(String id)

Sets the id of the root element of this component. The id is used with various APIs to identify the element, and it should be unique on the page.

Parameters:

id - the id to set, or "" to remove any previously set id

getId

public Optional<String> getId()

Gets the id of the root element of this component.

Returns:

the id, or and empty optional if no id has been set

See Also:

setId(String)

onAttach

protected void onAttach(AttachEvent attachEvent)

Called when the component is attached to a UI.

The default implementation does nothing.

This method is invoked before the AttachEvent is fired for the component.

Parameters:

attachEvent - the attach event

onDetach

protected void onDetach(DetachEvent detachEvent)

Called when the component is detached from a UI.

The default implementation does nothing.

This method is invoked before the DetachEvent is fired for the component.

Parameters:

detachEvent - the detach event

set

protected <T> void set(PropertyDescriptor<T,?> descriptor,
                       T value)

Sets the value of the given component property.

Type Parameters:

T - type of the value to set

Parameters:

descriptor - the descriptor for the property to set, not null

value - the new property value to set

See Also:

PropertyDescriptor

get

protected <T> T get(PropertyDescriptor<?,T> descriptor)

Gets the value of the given component property.

Type Parameters:

T - type of the value to get

Parameters:

descriptor - the descriptor for the property to set, not null

Returns:

the property value

See Also:

PropertyDescriptor

from

public static <T extends Component> T from(Element element,
                                           Class<T> componentType)

Creates a new component instance using the given element.

You can use this method when you have an element instance and want to use it through the API of a Component class.

This method attaches the component instance to the element so that Element.getComponent() returns the component instance. This means that getParent(), getChildren() and other methods which rely on Element -> Component mappings will work correctly.

Note that only one Component can be mapped to any given Element.

Type Parameters:

T - the component type to create

Parameters:

element - the element to wrap

componentType - the component type

Returns:

the component instance connected to the given element

See Also:

Element.as(Class)

setVisible

public void setVisible(boolean visible)

Sets the component visibility value.

When a component is set as invisible, all the updates of the component from the server to the client are blocked until the component is set as visible again.

Invisible components don't receive any updates from the client-side. Unlike the server-side updates, client-side updates, if any, are discarded while the component is invisible, and are not transmitted to the server when the component is made visible.

Parameters:

visible - the component visibility value

isVisible

public boolean isVisible()

Gets the component visibility value.

Returns:

true if the component is visible, false otherwise

onEnabledStateChanged

public void onEnabledStateChanged(boolean enabled)

Handle component enable state when the enabled state changes.

By default this sets or removes the 'disabled' attribute from the element. This can be overridden to have custom handling.

Parameters:

enabled - the new enabled state of the component

isTemplateMapped

protected boolean isTemplateMapped()

Gets whether this component was attached as part of a PolymerTemplate (by being mapped by an Id annotation), or if it was created directly.

Returns:

true when it was mapped inside a template, false otherwise

getTranslation

public String getTranslation(String key,
                             Object... params)

Get the translation for the component locale.

The method never returns a null. If there is no I18NProvider available or no translation for the key it returns an exception string e.g. '!{key}!'.

Parameters:

key - translation key

params - parameters used in translation string

Returns:

translation for key if found (implementation should not return null)

See Also:

getLocale()

getTranslation

public String getTranslation(String key,
                             Locale locale,
                             Object... params)

Get the translation for key with given locale.

The method never returns a null. If there is no I18NProvider available or no translation for the key it returns an exception string e.g. '!{key}!'.

Parameters:

key - translation key

locale - locale to use

params - parameters used in translation string

Returns:

translation for key if found

getLocale

protected Locale getLocale()

Gets the locale for this component.

It returns the UI locale if it has been set. If there is no UI locale available then it tries to use the first locale provided by the I18NProvider. If there is no any provided locale then the default locale is used.

Returns:

the component locale