EventHub

The EventHub module provides APIs to subscribe to, unsubscribe from, and trigger events.

NOTE

The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version. The APIs of this module can be used only in the stage model.

Modules to Import

import common from '@ohos.app.ability.common';

Usage

Before using any APIs in the EventHub, you must obtain an EventHub instance through the member variable context of the Ability instance.

import Ability from '@ohos.app.ability.UIAbility';
export default class MainAbility extends Ability {
    func1(){
        console.log('func1 is called');
    }
    onForeground() {
        this.context.eventHub.on('123', this.func1);
    }
}

EventHub.on

on(event: string, callback: Function): void;

Subscribes to an event.

System capability: SystemCapability.Ability.AbilityRuntime.Core

Parameters

Name	Type	Mandatory	Description
event	string	Yes	Event name.
callback	Function	Yes	Callback invoked when the event is triggered.

Example

import Ability from '@ohos.app.ability.UIAbility';

export default class MainAbility extends Ability {
    onForeground() {
        this.context.eventHub.on('123', this.func1);
        this.context.eventHub.on('123', () => {
            console.log('call anonymous func 1');
        });
        // Result
        // func1 is called
        // call anonymous func 1
        this.context.eventHub.emit('123'); 
    }
    func1() {
        console.log('func1 is called');
    }
}

EventHub.off

off(event: string, callback?: Function): void;

Unsubscribes from an event. If callback is specified, this API unsubscribes from the specified callback. If callback is not specified, this API unsubscribes from all callbacks in the event.

System capability: SystemCapability.Ability.AbilityRuntime.Core

Parameters

Name	Type	Mandatory	Description
event	string	Yes	Event name.
callback	Function	No	Callback for the event. If callback is unspecified, the given event with all callbacks is unsubscribed.

Example

import Ability from '@ohos.app.ability.UIAbility';

export default class MainAbility extends Ability {
    onForeground() {
        this.context.eventHub.on('123', this.func1);
        this.context.eventHub.off('123', this.func1); // Unsubscribe from func1.
        this.context.eventHub.on('123', this.func1);
        this.context.eventHub.on('123', this.func2);
        this.context.eventHub.off('123'); // Unsubscribe from func1 and func2.
    }
    func1() {
        console.log('func1 is called');
    }
    func2() {
        console.log('func2 is called');
    }
}

EventHub.emit

emit(event: string, ...args: Object[]): void;

Triggers an event.

System capability: SystemCapability.Ability.AbilityRuntime.Core

Parameters

Name	Type	Mandatory	Description
event	string	Yes	Event name.
...args	Object[]	Yes	Variable parameters, which are passed to the callback when the event is triggered.

Example

import Ability from '@ohos.app.ability.UIAbility';

export default class MainAbility extends Ability {
    onForeground() {
        this.context.eventHub.on('123', this.func1);
        // Result
        // func1 is called,undefined,undefined
        this.context.eventHub.emit('123');
        // Result
        // func1 is called,1,undefined
        this.context.eventHub.emit('123', 1);
        // Result
        // func1 is called,1,2
        this.context.eventHub.emit('123', 1, 2);
    }
    func1(a, b) {
        console.log('func1 is called,' + a + ',' + b);
    }
}