main.dart

import 'dart:convert';
import 'package:http/http.dart' as http;

class Example {
  Future<String> _getIPAdress() {
    final url = 'https://httpbin.org/ip';
    return http.get(url).then(response) {
      String ip = jsonDecode(response.body)['origin'];
      return ip;
    }
  }
}

main() {
  final example = new Example();
  example
    ._getIPAddress()
    .then((ip)) => print(ip)
    .catchError((error) => print(error));
}