如何在Dart中正确下载图片并转换为base64？

我很难下载图片然后将其显示在页面上。打印的 Base64 编码字符串看起来错误；它与例如不同http://www.freeformatter.com/base64-encoder.html结果。

这是我的代码：

HttpRequest.request(_url).then((HttpRequest response) {
    String contentType = response.getResponseHeader('Content-Type');

    if (_supportedContentType(contentType)) {
        List bytes = new Utf8Encoder().convert(response.responseText);
        String header = 'data:$contentType;base64,';
        String base64 = CryptoUtils.bytesToBase64(bytes);
        String image = "${header}${base64}";

        me.avatar = image;
        print(image);
    }
}

当您设置responseType时，您会得到二进制数据

import 'dart:html' show HttpRequest;
import 'dart:convert' show base64;
import 'dart:typed_data' show Uint8List, ByteBuffer;

main() {
  HttpRequest
      .request("Zacharie_Noterman_-_Monkey_business.jpg",
          responseType: "arraybuffer")
      .then((HttpRequest response) {
    String contentType = response.getResponseHeader('Content-Type');

    var list = new Uint8List.view((response.response as ByteBuffer));

    String header = 'data:$contentType;base64,';
    String base64 = base64.encode(list);
    String image = "${header}${base64}";

    //  me.avatar = image;
    print(image);
    //}
  });
}

result:

数据：图像/png；base64，/9j/4AAQSkZJRgABAQEAYABgAAD ....