according to the suggestions on the Internet, the code has been simplified and a picture has been made transparent
< image style= "height: 100% width: 100% src=: 0" src= " http://devimg.webf10.com/wech.; / >
 < view > 
 < image src= " http://devimg.webf10.com/wech.; data-src= " http://devimg.webf10.com/wech.; bindtap= "previewImage" / > 
 < / view > 
index.js
previewImage: function (e) {
var current = e.target.dataset.src;
console.log(current)
wx.previewImage({
  current: current,
  urls: [current]
})},
however, there is still no option to pop up the QR code on the real machine. It"s just that the picture is getting bigger, so ask for a successful demo
.