function hideMsg(that) {
  var animation = wx.createAnimation({
    duration: 1500,
    timingFunction: 'linear',
  })

  that.animation = animation

  animation.opacity(0).step()

  that.setData({
    animationData: animation.export()
  })

  setTimeout(() => {
    animation.opacity(1).step()
    that.setData({
      sendMsg: 
 
'',
      animationData: animation.export()
    })
  }, 1200)
}

每次呼叫結束後，都會將動畫重置，這是重複呼叫的核心！