harmony 鸿蒙@ohos.events.emitter (Emitter)

2022-08-09
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@ohos.events.emitter (Emitter)

The Emitter module provides the capabilities of sending and processing inter- or intra-thread events in a process. You can use the APIs of this module to subscribe to an event in persistent or one-shot manner, unsubscribe from an event, or emit an event to the event queue.

NOTE

The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version.

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 and executes a callback after the event is received.

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 to execute after the event is received.

Example

let innerEvent: emitter.InnerEvent = {
  eventId: 1
};

// Execute the callback after receiving the event whose eventId is 1.
emitter.on(innerEvent, () => {
  console.info('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 executed.

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 to execute after the event is received.

Example

let innerEvent: emitter.InnerEvent = {
    eventId: 1
};

// Execute the callback after receiving the event whose eventId is 1.
emitter.once(innerEvent, () => {
    console.info('once 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

// Unregister the callbacks of all events whose eventID is 1.
emitter.off(1);

emitter.off¹⁰⁺

off(eventId: number, callback: Callback<EventData>): void

Unsubscribes from an event. If the specified callback has been registered through the on or once API, it is unregistered. Otherwise, no processing is performed.

System capability: SystemCapability.Notification.Emitter

Parameters

Name	Type	Mandatory	Description
eventId	number	Yes	Event ID.
callback¹⁰⁺	Callback<EventData>	Yes	Callback to unregister.

Example

// Unregister the emitterCallback callback for the event whose eventID is 1.
// If the callback has not been registered, no processing is performed.
emitter.off(1, () => {
  console.info('callback');
});

emitter.emit

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

Emits an event.

System capability: SystemCapability.Notification.Emitter

Parameters

Name	Type	Mandatory	Description
event	InnerEvent	Yes	Event to emit, where EventPriority specifies the emit priority of the event.
data	EventData	No	Data carried by the event.

Example

let eventData: emitter.EventData = {
    data: {
        "content": "c",
        "id": 1,
    }
};

let innerEvent: emitter.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 event to subscribe to or emit. The EventPriority settings do not take effect under event subscription.

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.