Emitter

Note: The initial APIs of this module are supported since API version 7.

Modules to Import

import emitter from '@ohos.events.emitter'

Required Permissions

None

EventPriority

Enumerates the event emit priority levels.

Name	Value	Description
IMMEDIATE	0	The event will be emitted immediately. System capability: SystemCapability.Notification.Emitter
HIGH	1	The event will be emitted before low-priority events. System capability: SystemCapability.Notification.Emitter
LOW	2	The event will be emitted before idle-priority events. By default, an event is in LOW priority. System capability: SystemCapability.Notification.Emitter
IDLE	3	The event will be emitted after all the other events. System capability: SystemCapability.Notification.Emitter

emitter.on

on(event: InnerEvent, callback: Callback<EventData>): void

Subscribes to an event in persistent manner. This API uses a callback to return the event.

System capability: SystemCapability.Notification.Emitter

Parameters

Name	Type	Mandatory	Description
event	InnerEvent	Yes	Event to subscribe to in persistent manner.
callback	Callback<EventData>	Yes	Callback used to return the event.

Example

var innerEvent = {
    eventId: 1
};
var callback = (eventData) => {
    console.info('callback');
};
emitter.on(innerEvent, callback);

emitter.once

once(event: InnerEvent, callback: Callback<EventData>): void

Subscribes to an event in one-shot manner and unsubscribes from it after the event callback is received.

System capability: SystemCapability.Notification.Emitter

Parameters

Name	Type	Mandatory	Description
event	InnerEvent	Yes	Event to subscribe to in one-shot manner.
callback	Callback<EventData>	Yes	Callback used to return the event.

Example

var innerEvent = {
    eventId: 1
};
var callback = (eventData) => {
    console.info('once callback');
};
emitter.once(innerEvent, callback);

emitter.off

off(eventId: number): void

Unsubscribes from an event.

System capability: SystemCapability.Notification.Emitter

Parameters

Name	Type	Mandatory	Description
eventId	number	Yes	Event ID.

Example

emitter.off(1);

emitter.emit

emit(event: InnerEvent, data?: EventData): void

Emits an event to the event queue.

System capability: SystemCapability.Notification.Emitter

Parameters

Name	Type	Mandatory	Description
event	InnerEvent	Yes	Event to emit.
data	EventData	No	Data carried by the event.

Example

var eventData = {
    data: {
        "content": "c",
        "id": 1,
    }};
var innerEvent = {
    eventId: 1,
    priority: emitter.EventPriority.HIGH
};
emitter.emit(innerEvent, eventData);

InnerEvent

Describes an intra-process event.

Name	Type	Readable	Writable	Description
eventId	number	Yes	Yes	Event ID, which is used to identify an event. System capability: SystemCapability.Notification.Emitter
priority	EventPriority	Yes	Yes	Emit priority of the event. System capability: SystemCapability.Notification.Emitter

EventData

Describes the data passed in the event.

Name	Type	Readable	Writable	Description
data	[key: string]: any	Yes	Yes	Data carried by the event. The data type can be String, Integer, or Boolean. System capability: SystemCapability.Notification.Emitter