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title Observable
titleTemplate title - API / NativeScript
description Observable is used when you want to be notified when a change occurs. Use on/off methods to add/remove listener. Please note that should you be using the `ne...
contributors false

Defined in: data/observable/index.ts

Observable is used when you want to be notified when a change occurs. Use on/off methods to add/remove listener. Please note that should you be using the new Observable({}) constructor, it is obsolete since v3.0, and you have to migrate to the "data/observable" fromObject({}) or the fromObjectRecursive({}) functions.

Extended by

Constructors

Constructor

new Observable(): Observable;

Returns

Observable

Properties

propertyChangeEvent

static propertyChangeEvent: string;

Defined in: data/observable/index.ts

String value used when hooking to propertyChange event.

Ns Event

propertyChange

Methods

_createPropertyChangeData()

_createPropertyChangeData(
   propertyName: string, 
   value: any, 
   oldValue?: any): PropertyChangeData;

Defined in: data/observable/index.ts

This method is intended to be overriden by inheritors to provide additional implementation.

Parameters

Parameter Type
propertyName string
value any
oldValue? any

Returns

PropertyChangeData

_emit()

_emit(eventName: string): void;

Defined in: data/observable/index.ts

Parameters

Parameter Type
eventName string

Returns

void

addEventListener()

addEventListener(
   eventName: string, 
   callback: (data: EventData) => void, 
   thisArg?: any, 
   once?: boolean): void;

Defined in: data/observable/index.ts

Adds a listener for the specified event name.

Parameters

Parameter Type Description
eventName string Name of the event to attach to.
callback (data: EventData) => void A function to be called when some of the specified event(s) is raised.
thisArg? any An optional parameter which when set will be used as "this" in callback method call.
once? boolean An optional parameter which when set will cause the event listener to fire once.

Returns

void

get()

get(name: string): any;

Defined in: data/observable/index.ts

Gets the value of the specified property.

Parameters

Parameter Type
name string

Returns

any

hasListeners()

hasListeners(eventName: string): boolean;

Defined in: data/observable/index.ts

Checks whether a listener is registered for the specified event name.

Parameters

Parameter Type Description
eventName string The name of the event to check for.

Returns

boolean

notify()

notify<T>(data: T): void;

Defined in: data/observable/index.ts

Notify this Observable instance with some data. This causes all event handlers on the Observable instance to be called, as well as any 'global' event handlers set on the instance's class.

Type Parameters

Type Parameter
T extends Optional<EventData, "object">

Parameters

Parameter Type Description
data T an object that satisfies the EventData interface, though with an optional 'object' property. If left undefined, the 'object' property will implicitly be set as this Observable instance.

Returns

void

notifyPropertyChange()

notifyPropertyChange(
   name: string, 
   value: any, 
   oldValue?: any): void;

Defined in: data/observable/index.ts

Notifies all the registered listeners for the property change event.

Parameters

Parameter Type
name string
value any
oldValue? any

Returns

void

off()

off(
   eventName: string, 
   callback?: (data: EventData) => void, 
   thisArg?: any): void;

Defined in: data/observable/index.ts

Removes the listener(s) for the specified event name.

Parameters

Parameter Type Description
eventName string The name of the event.
callback? (data: EventData) => void An optional specific event listener to remove (if omitted, all event listeners by this name will be removed).
thisArg? any An optional parameter which, when set, will be used to refine search of the correct event listener to be removed.

Returns

void

on()

on(
   eventName: string, 
   callback: (data: EventData) => void, 
   thisArg?: any): void;

Defined in: data/observable/index.ts

Adds a listener for the specified event name.

Parameters

Parameter Type Description
eventName string The name of the event.
callback (data: EventData) => void The event listener to add. Will be called when an event of the given name is raised.
thisArg? any An optional parameter which, when set, will be bound as the this context when the callback is called. Falsy values will be not be bound.

Returns

void

once()

once(
   eventName: string, 
   callback: (data: EventData) => void, 
   thisArg?: any): void;

Defined in: data/observable/index.ts

Adds a listener for the specified event name, which, once fired, will remove itself.

Parameters

Parameter Type Description
eventName string The name of the event.
callback (data: EventData) => void The event listener to add. Will be called when an event of the given name is raised.
thisArg? any An optional parameter which, when set, will be bound as the this context when the callback is called. Falsy values will be not be bound.

Returns

void

removeEventListener()

removeEventListener(
   eventName: string, 
   callback?: (data: EventData) => void, 
   thisArg?: any): void;

Defined in: data/observable/index.ts

Removes listener(s) for the specified event name.

Parameters

Parameter Type Description
eventName string Name of the event to attach to.
callback? (data: EventData) => void An optional parameter pointing to a specific listener. If not defined, all listeners for the event names will be removed.
thisArg? any An optional parameter which when set will be used to refine search of the correct callback which will be removed as event listener.

Returns

void

set()

set(name: string, value: any): void;

Defined in: data/observable/index.ts

Updates the specified property with the provided value.

Parameters

Parameter Type
name string
value any

Returns

void

setProperty()

setProperty(name: string, value: any): void;

Defined in: data/observable/index.ts

Updates the specified property with the provided value and raises a property change event and a specific change event based on the property name.

Parameters

Parameter Type
name string
value any

Returns

void

addEventListener()

static addEventListener(
   eventName: string, 
   callback: (data: EventData) => void, 
   thisArg?: any, 
   once?: boolean): void;

Defined in: data/observable/index.ts

Please avoid using the static event-handling APIs as they will be removed in future.

Parameters

Parameter Type
eventName string
callback (data: EventData) => void
thisArg? any
once? boolean

Returns

void

Deprecated

off()

static off(
   eventName: string, 
   callback?: (data: EventData) => void, 
   thisArg?: any): void;

Defined in: data/observable/index.ts

Please avoid using the static event-handling APIs as they will be removed in future.

Parameters

Parameter Type
eventName string
callback? (data: EventData) => void
thisArg? any

Returns

void

Deprecated

on()

static on(
   eventName: string, 
   callback: (data: EventData) => void, 
   thisArg?: any, 
   once?: boolean): void;

Defined in: data/observable/index.ts

Please avoid using the static event-handling APIs as they will be removed in future.

Parameters

Parameter Type
eventName string
callback (data: EventData) => void
thisArg? any
once? boolean

Returns

void

Deprecated

once()

static once(
   eventName: string, 
   callback: (data: EventData) => void, 
   thisArg?: any): void;

Defined in: data/observable/index.ts

Please avoid using the static event-handling APIs as they will be removed in future.

Parameters

Parameter Type
eventName string
callback (data: EventData) => void
thisArg? any

Returns

void

Deprecated

removeEventListener()

static removeEventListener(
   eventName: string, 
   callback?: (data: EventData) => void, 
   thisArg?: any): void;

Defined in: data/observable/index.ts

Please avoid using the static event-handling APIs as they will be removed in future.

Parameters

Parameter Type
eventName string
callback? (data: EventData) => void
thisArg? any

Returns

void

Deprecated