需求：生成一个商品详细页面的二维码(带分享者的id参数），别人扫码后到达指定商品页面，并获取参数中的分享者id。 

服务器端使用.net调用微信的api接口，使用的代码如下

string postUrl = "https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=" + access_token;
HttpWebRequest request = WebRequest.Create(postUrl) as HttpWebRequest;
request.Method = "POST";
request.ContentType = "application/json;charset=UTF-8";

string options = "{\"scene\":\"" + scene + "\",\"page\":\"pages/index/index\",\"width\":\"1024\"}";
byte[] payload = Encoding.UTF8.GetBytes(options);
request.ContentLength = payload.Length;

Stream writer = request.GetRequestStream();
writer.Write(payload, 0, payload.Length);
writer.Close();

System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)request.GetResponse();
System.IO.Stream stream = response.GetResponseStream();
List<byte> bytes = new List<byte>();
int temp = stream.ReadByte();
while (temp != -1)
{
　　bytes.Add((byte)temp);
　　temp = stream.ReadByte();
}
byte[] result = bytes.ToArray();
string base64 = Convert.ToBase64String(result);//将byte[]转为base64
return "{\"errcode\":0,\"errmsg\":\"获取成功\",\"buffer\":\"" + base64 + "\"}";

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接着在微信小程序端用以下代码

onLoad: function (options) {

var that=this;

var para = {

action: 'wx_ewm',

scene: '',

}

wx.request({

url: app.config.hostUrl + 'wx/config.aspx',

data: para,

success: function (res) {

var base64 = res.data.buffer.replace(/[\r\n]/g, "");

that.setData({

ewm_url: "data:image/png;base64," + base64

})

},

fail: function () {

wx.hideToast();

console.log('error!!!!!!!!!!!!!!')

}

})

},

在wxml用<image src="{{ewm_url}}" width="300" height="300"></image>显示不出图片

1、是哪里出了问题吗？

2、在模拟器、真机调试都无法显示出图片。

请教大家。谢谢