事件中心，提供订阅、取消订阅、触发事件的能力

使用说明

在使用eventHub的功能前，需要通过Ability实例的成员变量context获取。

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;

订阅指定事件。

系统能力：SystemCapability.Ability.AbilityRuntime.Core

参数：

示例：

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');
        });
        // 结果：
        // 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;

取消订阅指定事件。当callback传值时，取消订阅指定的callback；未传值时，取消订阅该事件下所有callback。

系统能力：SystemCapability.Ability.AbilityRuntime.Core

参数：

示例：

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); //取消订阅func1
        this.context.eventHub.on('123', this.func1);
        this.context.eventHub.on('123', this.func2);
        this.context.eventHub.off('123');  //取消订阅func1和func2
    }
    func1() {
        console.log('func1 is called');
    }
    func2() {
        console.log('func2 is called');
    }
}

EventHub.emit

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

触发指定事件。

系统能力：SystemCapability.Ability.AbilityRuntime.Core

参数：

示例：

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

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