dio-proxy.dart

// Make sure to replace <YOUR_LOCAL_IP> with 
// the external IP of your computer if you're using Android. 
// Note that we're using port 8888 which is Charles' default.
String proxy = Platform.isAndroid ? '<YOUR_LOCAL_IP>:8888' : 'localhost:8888';

// Create a new Dio instance.
Dio dio = Dio();

// Tap into the onHttpClientCreate callback
// to configure the proxy just as we did earlier.
(dio.httpClientAdapter as DefaultHttpClientAdapter).onHttpClientCreate = (client) { 
  // Hook into the findProxy callback to set the client's proxy.
  client.findProxy = (url) {
    return 'PROXY $proxy';
  };
  
  // This is a workaround to allow Charles to receive
  // SSL payloads when your app is running on Android.
  client.badCertificateCallback = (X509Certificate cert, String host, int port) => Platform.isAndroid;
}