我正在使用protobuf和gRPC在Flutter应用程序和python服务器（Flutter中的客户端和python中的服务器）之间交换信息。服务器运行在www.example.com上0.0.0.0，客户端使用服务器计算机的IP地址。

import 'dart:async';
import 'User.pbgrpc.dart';
import 'User.pb.dart';
import 'package:grpc/grpc.dart';

Future<Null> main() async {
  final channel = new ClientChannel('IP_ADDRESS',
      port: 50051,
      options: const ChannelOptions(
          credentials: const ChannelCredentials.insecure()));
  final stub = new StorageClient(channel);

  Test input = new Test();
  input.id = 1;
  try {
    var response = await stub.getPerson(input);
    print('Greeter client received: ${response}');
  } catch (e) {
    print('Caught error: $e');
  }
  await channel.shutdown();
}

如果我使用dart client.dart运行这个客户端，一切正常，得到了预期的响应。但是如果我把这个方法嵌入到flutter应用中，比如：

@override
Widget build(BuildContext context) {

Future<Null> testRPC() async {
  final channel = new ClientChannel('IP_ADDRESS',
      port: 50051,
      options: const ChannelOptions(
          credentials: const ChannelCredentials.insecure()));
  final stub = new StorageClient(channel);

  Test input = new Test();
  input.id = 1;
  try {
    var response = await stub.getPerson(input);
    print('Greeter client received: ${response}');
  } catch (e) {
    print('Caught error: $e');
  }
  await channel.shutdown();
}

testRPC();
...etc
}

我得到：

I/flutter (18824): Caught error: gRPC Error (14, Error connecting: SocketException: OS Error: No route to host, errno = 111, address = localhost, port = 45638)

**更新：**当我用模拟器运行应用程序时，它正在工作。所以这是只在使用真实的设备时发生的错误。