使用vue.set方法失败

mounted(){
    this.$bus.$on('imgUrl', function (data) {
      // this.swiperUrl = data
      this.$set(this.swiperUrl,"Url",data.Url)
      console.log(444444444, this.swiperUrl)
      this.$forceUpdate()
    })
  }

报错：
Error in event handler for "imgUrl": "TypeError: Cannot use 'in' operator to search for 'Url' in undefined"

this.swiperUrl 里没有 Url属性吧 你打印看看