<canvas  class="share_canvas" type="2d" id="myCanvas" ></canvas>

onShow() {
    let that = this
    that.downShareImage()
  },
/**
   * 
   * 下载要分享的图片
   */
  downShareImage() {
    console.log('下载要分享的图片')
    const that = this
    wx.downloadFile({
      url: 'https://img0.baidu.com/it/u=925998594,1358415170&fm=253&fmt=auto&app=138&f=JPEG?w=500&h=281',
      success(res) {

        // console.log(res.tempFilePath)
        that.drawShareImg(res.tempFilePath);
      },
      fail(error) {
        console.log(error)
      }
    })
  },

  async drawShareImg(img) {
    console.log('又进来了')
    let that = this
    let {
      canvas,
      ctx,
    } = that.data
    const dpr = wx.getSystemInfoSync().pixelRatio
    console.log(dpr)
    wx.createSelectorQuery().select('#myCanvas')
      .fields({
        node: true,
        size: true
      })
      .exec((res) => {
        canvas = res[0].node
        ctx = canvas.getContext('2d')
        console.log(res[0])
        canvas.width = res[0].width * dpr
        canvas.height = res[0].height * dpr
        ctx.scale(dpr, dpr)
        // 绘制黑色背景
        ctx.fillStyle = 'rgba(0, 0, 0, 1)';
        ctx.fillRect(0, 0, 462, 343)

        let bg = canvas.createImage()
        bg.src = '/images/share_bg.png'
        bg.onload = () => {
          ctx.drawImage(bg, 0, 0, 462, 343);
          ctx.restore()
        }
        let goodimg = canvas.createImage()
        goodimg.src = img
        goodimg.onload = () => {
          ctx.drawImage(goodimg, 250, 80, 150, 150);
          ctx.restore()
        }
        setTimeout(function () {
          ctx.font = '14px sans-serif';
          ctx.fillStyle = '#000';
          let str = '商品名称商品名称商品名称商品名称名称名称'
          for (var i = 0; i < str.length; i++) {
            if (ctx.measureText(str.substring(0, i + 1)).width > 140) {
              ctx.fillText(str.substring(0, i), 60, 98, 140)
              ctx.fillText(str.substring(i), 60, 120, 140)
              break
            }
          }
          ctx.font = '14px sans-serif';
          ctx.fillStyle = '#000';
          ctx.fillText('订单金额', 61, 194)
          ctx.font = '14px sans-serif';
          ctx.fillStyle = '#FBAB2A';
          ctx.fillText('￥', 61, 225)
          ctx.font = '18px sans-serif';
          ctx.fillStyle = '#FBAB2A';
          ctx.fillText('899.99', 75, 226)

          wx.canvasToTempFilePath({
            canvas: canvas,
            x: 0,
            y: 0,
            width: 462,
            height: 343,
            destWidth: 500,
            destHeight: 400,
            success: res => {
              // 生成的图片临时文件路径
              const tempFilePath = res.tempFilePath
              console.log('最后生成', tempFilePath)
              that.setData({
                shareImg: tempFilePath
              })
              wx.hideToast();
            },
            fail: (err) => {
              wx.hideToast();
            }
          }, that)
        }, 1000)
      })
  }
onShareAppMessage(e) {
    const that = this
    return {
      title: `向你推荐，商品名称`,
      path: "../pages/goods-detail/goods-detail",
      imageUrl: that.data.shareImg
    }
  },