自定义ImageProvider以支持https

NetworkImageSSL

class NetworkImageSSL extends ImageProvider<NetworkImageSSL> {
  const NetworkImageSSL(this.url, {this.scale = 1.0, this.headers})
      : assert(url != null),
        assert(scale != null);

  final String url;

  final double scale;

  final Map<String, String> headers;

  @override
  Future<NetworkImageSSL> obtainKey(ImageConfiguration configuration) {
    return new SynchronousFuture<NetworkImageSSL>(this);
  }

  @override
  ImageStreamCompleter load(NetworkImageSSL key) {
    return new MultiFrameImageStreamCompleter(
        codec: _loadAsync(key),
        scale: key.scale,
        informationCollector: () {
          List<DiagnosticsNode> informationCollector;
          informationCollector.add(DiagnosticsProperty('Image provider', this));
          informationCollector.add(DiagnosticsProperty('Image key', key));
          return informationCollector;
        });
  }

  static final HttpClient _httpClient = new HttpClient()
    ..badCertificateCallback = ((X509Certificate cert, String host, int port) {
      ///add https certificate check 
      return true;
    });

  Future<ui.Codec> _loadAsync(NetworkImageSSL key) async {
    assert(key == this);

    final Uri resolved = Uri.base.resolve(key.url);
    final HttpClientRequest request = await _httpClient.getUrl(resolved);
    headers?.forEach((String name, String value) {
      request.headers.add(name, value);
    });
    final HttpClientResponse response = await request.close();
    if (response.statusCode != HttpStatus.ok) {
      throw new Exception('HTTP request failed, statusCode: ${response?.statusCode}, $resolved');
    }

    final Uint8List bytes = await consolidateHttpClientResponseBytes(response);
    if (bytes.lengthInBytes == 0) {
      throw new Exception('NetworkImageSSL is an empty file: $resolved');
    }
    return await ui.instantiateImageCodec(bytes);
  }

  @override
  bool operator ==(dynamic other) {
    if (other.runtimeType != runtimeType) return false;
    final NetworkImageSSL typedOther = other;
    return url == typedOther.url && scale == typedOther.scale;
  }

  @override
  int get hashCode => hashValues(url, scale);

  @override
  String toString() => '$runtimeType("$url", scale: $scale)';
}