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 |