code: function touchHandler (event) {
    let opt = this._opt
    opt.preventDefault && event.preventDefault()
    opt.stopPropagation && event.stopPropagation()
  
    // 如果 touchstart 没有被触发(可能被子元素的 touchstart 回调触发了 stopPropagation)，
    // 那么后续的手势将取消计算
    if (event.type !== 'touchstart' && !dataProcessor.startTime) {
      return
    }
  
    let data = dataProcessor.process(event, opt.preventX, opt.preventY)
    this._recognize(data)
    this.trigger(event.type, event, data)
  }
docs: Handle touch event.
  
  @inner
  @param {Event} event event