@ohos.events.emitter

The Emitter module provides APIs for sending and processing in-process events, including the APIs for processing events that are subscribed to in persistent or one-shot manner, unsubscribing from events, and emitting events to the event queue.

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

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. The EventPriority settings do not take effect.
callback	Callback<EventData>	Yes	Callback used to return the event.

Example

let innerEvent = {
    eventId: 1
};
function EmitterCallback(eventData) {
    console.info('callback');
}
emitter.on(innerEvent, EmitterCallback);

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. The EventPriority settings do not take effect.
callback	Callback<EventData>	Yes	Callback used to return the event.

Example

let innerEvent = {
    eventId: 1
};
function EmitterCallback(eventData) {
    console.info('once callback');
};
emitter.once(innerEvent, EmitterCallback);

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

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

EventPriority

Enumerates the event emit priority levels.

System capability: SystemCapability.Notification.Emitter

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

InnerEvent

Describes an in-process event.

System capability: SystemCapability.Notification.Emitter

Name	Type	Readable	Writable	Description
eventId	number	Yes	Yes	Event ID.
priority	EventPriority	Yes	Yes	Emit priority of the event.

EventData

Describes the data passed in the event.

System capability: SystemCapability.Notification.Emitter

Name	Type	Readable	Writable	Description
data	[key: string]: any	Yes	Yes	Data carried by the event. The value can be a string, integer, or Boolean, wherein a string contains a maximum of 10240 bytes.