微信小程序开发-ctx.draw无反应

要记得在页面中写入画布的代码

<view class='mask'  catchtouchmove="move" wx-if="{{qrTempPath}}" >
  <image style="width: {{userEquip.windowWidth}}rpx;height: {{canvasHeight}}px;"  mode="widthFix" src="{{qrTempPath}}" bindtap='closeQRImage'></image>
   <button class='saveToShare' bindtap='saveToShare'>保存至相册，分享到朋友圈</button>
</view>

<view  ><canvas  canvas-id="firstCanvas"  style="width: {{userEquip.windowWidth}}rpx;height: {{canvasHeight}}px;position:fixed;top:-9999px" ></canvas></view>