harmony 鸿蒙EventHub

2022-12-22
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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 UIAbility instance.

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

export default class EntryAbility extends UIAbility {
    eventFunc(){
        console.log('eventFunc is called');
    }

    onForeground() {
        this.context.eventHub.on('myEvent', this.eventFunc);
    }
}

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

export default class EntryAbility extends UIAbility {
    onForeground() {
        this.context.eventHub.on('myEvent', this.eventFunc);
        // Anonymous functions can be used to subscribe to events.
        this.context.eventHub.on('myEvent', () => {
            console.log('call anonymous eventFunc');
        });
        // Result
        // eventFunc is called
        // call anonymous eventFunc
        this.context.eventHub.emit('myEvent'); 
    }

    eventFunc() {
        console.log('eventFunc is called');
    }
}

EventHub.off

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

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

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

export default class EntryAbility extends UIAbility {
    onForeground() {
        this.context.eventHub.on('myEvent', this.eventFunc1);
        this.context.eventHub.off('myEvent', this.eventFunc1); // Unsubscribe from the myEvent event with the callback eventFunc1.
        this.context.eventHub.on('myEvent', this.eventFunc1);
        this.context.eventHub.on('myEvent', this.eventFunc2);
        this.context.eventHub.off('myEvent');  // Unsubscribe from the myEvent event with all the callbacks (eventFunc1 and eventFunc2).
    }

    eventFunc1() {
        console.log('eventFunc1 is called');
    }

    eventFunc2() {
        console.log('eventFunc2 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[]	No	Variable parameters, which are passed to the callback when the event is triggered.

Example

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

export default class EntryAbility extends UIAbility {
    onForeground() {
        this.context.eventHub.on('myEvent', this.eventFunc);
        // Result
        // eventFunc is called,undefined,undefined
        this.context.eventHub.emit('myEvent');
        // Result
        // eventFunc is called,1,undefined
        this.context.eventHub.emit('myEvent', 1);
        // Result
        // eventFunc is called,1,2
        this.context.eventHub.emit('myEvent', 1, 2);
    }

    eventFunc(argOne: number, argTwo: number) {
        console.log(`eventFunc is called, ${argOne}, ${argTwo}`);
    }
}