通过自定义的组件实例，怎么调用子组件方法并传参啊？

https://developers.weixin.qq.com/miniprogram/dev/framework/custom-component/events.htmlhttps://developers.weixin.qq.com/miniprogram/dev/framework/open-ability/getPhoneNumber.html

behaviors: ['wx://component-export'],

export: function() {

return { myField: this.a() }

},

this.selectComponent('#the-id').myField

这样可以调用a方法，但是怎么传参呢