I went to the terminal and used ifconfig command

I got my IP address: 192.168.0.109

Then I simply replaced this IP address with my "localhost" in flutter app http requests. And it worked like a charm!

• if in localhost instead localhost use the IP of your network
• hint:for find Ip in cmd run ipconfig and get the ipv4

1: Example:

await http.post("http://127.68.34.23/wp-json/...",
                    headers: headers,
                    body: json.encode(data))

if in server write the url of main in url

I had the same problem running in a real device, and only changing the IP in API link doesn´t work.

The solution for me was to put the server run with the command below:

manage.py runserver 0.0.0.0:8000

Then pass your machine IP to the API link instead of localhost, as the sample below:

http://192.168.0.67:8000

In addition to Rohan’s answer you can also read:

Unable to make calls to Localhost using Flutter, random port being assigned to HTTP GET call

I was trying to run my app on physical device using local server so, for that i had to use the below mentioned command, here keep in mind change the port number according to your own port number

adb reverse tcp:3001 tcp:3001

As @maheshmnj pointed that this command is redirecting your phone’s
port 3001 to your computer’s port 3001. In case if you want to
redirect port 2000 of your phone to port 3000 of your computer then
you could do this adb reverse tcp:2000 tcp:3000

you can also read about adb and networking via going through below mentioned page
https://developer.android.com/studio/command-line/adb.html

This problem occurs when the endpoint are incorrect or your host and server backend (Example Laravel API)doesn’t share the same IP address.

Solution is.

1. Connect your workspace (computer, emulator, devices) in the same
   network.
2. Find your IP by typing on terminal ifconfig.
3. If you build your API with Laravel, start the server appointing to IP ADDRESS of your computer, sudo php artisan serve --host YOUR_COMPUTER_IP_ADDRESS --port NUMBER

Example:

`sudo php artisan serve --host 192.168.1.11 --port 80`

4. Test your endpoint in Postman or similar Application and type http://192.168.1.11:80/Your_Route
5. If everything is working good, you can run with app. Go!!!

Try adding <uses-permission android:name="android.permission.INTERNET"/> to your manifest. This solved this issue for me.

I know that the question is too old, But I will answer this because this may be helpful to someone who has this problem.

Without more details, I can’t give a specific solution. But with following conditions can give a specific solution

• I imagine that the API host was in local computer
• I imagine that you use your emulator for running the app

The URL you tried with postman maybe something like this http://127.0.0.1:[port number]/register or http://localhost:[port number]/register. But this may not work with an emulator because it doesn’t have access to that URL. To get access to the local host of your you need to find out the host address.

Follow these steps to get your host address.

• Click on the three dots(More) in the android emulator
• Setting -> Proxy
• You can change your host address if you like by selecting `Manual proxy configuration

Then you can see your host name with the port number. Then replace your URL with those like http://10.0.0.2:5000/register.

In C#[.net core api], go to launchSettings.json under Properties tab and change the follwing code to this(change localhost to 0.0.0.0 on applicationURl) and on the app(flutter), use ur local IPV4 IP. ex: (192.169.0.10)

"coreWebAPI": {
      "commandName": "Project",
      "launchBrowser": false,
      "launchUrl": "api/values",
      "applicationUrl": "http://0.0.0.0:5000", 
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    }

If you are using ‘localhost’ in your url, change it to your ipv4 address and it will work

Soltuion that worked on my machine

[√] Flutter (Channel stable, 2.5.3, on Microsoft Windows [Version 10.0.19043.1288], locale en-US)
[√] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
[√] Chrome - develop for the web
[√] Android Studio (version 2020.3)
[√] VS Code (version 1.61.2)
[√] Connected device (3 available)

STEP: 1 (get your ipv4)

in terminal/cmd type

• ifconfig for Mac/Linux/Unix
• ipconfig for Windows

you will get some result in windows it looks like

STEP: 2 (change your request url)

❌ Dont do

• http.get('localhost/my-local-rest-api/etc'
• 127.0.0.1//my-local-rest-api/etc.

✅ Do

• for android http.get('10.0.2.2/my-local-rest-api/etc
• for ios http.get('192.168.8.155/my-local-rest-api/etc

IMPORTANT

⚠ always pass Uri instead of raw String
example: http.get(Uri.parse('my-url-in-raw-string'))

STEP 3: enable un-encrypted networking connections

for Android

in android/app/src/debug/AndroidManifest.xml

<manifest ...other params...>
   // STEP: 1 make sure you have INTERNET permission
   <uses-permission android:name="android.permission.INTERNET" />

   <application
        android:label="YourAppName"
        android:usesCleartextTraffic="true"> <-- STEP: 2 add this line
        <activity
    </application>
</manifest>

for iOS

in ios/Runner/Info.plist add this

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsLocalNetworking</key>
    <true/>
</dict>

This is what I had to change to fix the same error in my case:

• Start django with python manage.py runserver 0:8000 and not just python manage.py runserver (0:8000 is the abbreviation for 0.0.0.0:8000 and makes your web application visible on your local network – see https://docs.djangoproject.com/en/3.0/ref/django-admin/#runserver)
• In your flutter app specify the server address using your pc local ip, i.e. instead of http://localhost:8000 use something like http://192.168.1.2:8000. To retrieve your current ip address run ipconfig in the terminal if on Windows, otherwise ifconfig.
• Update allowed host in django settings if necessary. For example set ALLOWED_HOSTS = ['*', ] (but only in your dev environment!)

What you need to do is to get your public PC IP and use it in your URL for example:
http://192.168.0.67:3000, where 3000 is the port no.

For mac users to check ip address

in terminal type: ipconfig getifaddr en0 and use that Ip address as below

import 'dart:io';

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

class AuthAction {
  static String BASE_URL = 'http://192.168.0.105:27017/';

  static Future<Null> signUpAction(
      firstName, lastName, email, password, userName) async {
    try {
      http.Response res = await http.post( Uri.parse(BASE_URL + 'signUp' ));
      print(res);

      if (res.statusCode == 200) {
      }
    } catch (err) {
      print(err);

        // Fluttertoast.showToast(msg: 'err');
    }
  }
}

Note: I did not touch the port on which my mongo-node server is running. Which is 27017

Recently I also faced a similar issue, there are a few things you try and check (its applicable for both flutter or android with any backend language):

If you are testing on an android emulator

1.You should first get the ipv4 of your PC ( for mac type this in terminal ipconfig getifaddr en0)

3. Use this ip address in URI (hostname) while sending the request.

4. Go to Emulator settings -> proxy and select Manual proxy configuration and paste your PC ip address and port number as your local server port usually 3000.

5. Restart your emulator (this is necessary).

6. It should work, if it’s not working then restart your application and carefully check the whole URL. I am telling you this because I was passing extra ‘/’ before.

If you are testing on a physical device

1. Make sure your device and PC are connected to the same network (using a mobile hotspot will be better).
2. Get the ipv4 of your PC from the terminal and use this in URI (hostname) while sending the request.
3. It should work, if it’s not then check your URL carefully.

Not the best solution in the world but a good workaround is to install ngrok and link your localhost to it. Worked fine for me and it’s very fast to setup.

I fixed this with $ adb tcpip <port-your-local-server>

I had the same issue in flutter with spring backend. Instead of using
‘http://localhost:8080/’ in my requests, I changed this to ‘http://143.235.7.641:8080/’ where ‘143.235.7.641’ is my Wi-Fi IPv4 address, and it worked.

(NOTE : I assume you are testing flutter in physical phone,and phone and computer are connected the same wi-fi.)

add in you Androidmenifest file project->app->src->AndroidManifest.xml

Title: Connecting Flutter App on Physical Device to Flask Server

Solution
Follow these steps to achieve the desired connection:

Run Flask Server:

Start your Flask server and make it accessible over the network using the following command:

flask run --debug --host 0.0.0.0

Find Your Machine’s IP Address:

Obtain your machine’s IP address (IPv4) by running the following command (on Ubuntu):

hostname -I

Replace localhost with this IP address in your Flutter app code.

Update Flutter App Code:

In your Flutter app, replace references to localhost with your machine’s IP address obtained in the previous step. Update the URLs or endpoints accordingly.

Example:

final serverUrl = 'http://your_machine_ip:5000/endpoint';

Connect Devices to the Same Wi-Fi Network:

Ensure that your physical device and your development machine (running the Flask server) are connected to the same Wi-Fi network.

Access the Flask Server from Flutter App:

Run your Flutter app on the physical device, and it should be able to access the Flask server using the updated IP address.

I had this same issue once,
After going through some overly complicated stackoverflow answers and google search, finally i figure it out,
In this case you are most likely to be using a android emulator, So just turn on the mobile data on the emulator then try it again, i’m sure that this time it will work.

final response = await client.post(
    "http://192.xxx.xx.xx/api/signin", 
    headers: {"Authorization": apiKey},
    body: jsonEncode({
      "username": username,
      "password": password,
    }));

Even I had got a SocketException Error but I replaced my IP address and didn’t mention any Port number and it worked for me, and if I mention the port number it would throw an error.
Hoping this would work out.

I am using Flask for backend ,using blocs.

Try ths link delay the fuction and your will not get this error

Future.delayed(const Duration(milliseconds: 500), () {
    widget.callback();
  });

It Work for me

If you are running on real phone, then you will get this error even if you add your localhost address to allowed host.
For me, connecting my laptop to my phone’s hotspot and running django server with laptop’s ipv4 address (which you can find by using ipconfig command) by python manage.py runserver 192.168..:8000 i.e. your ipv4 address:port number, than you will be able to access django server using your phone’s browser as well, now add this your ipv4 address to your allowed host. And, change your url from localhost or 127.0.0.1 to your ipv4 address. I hope this resolves your issue.

Replace your URL with:

Uri.parse("YourURL").replace(host: "YourIPAddress");

Explanation: This error means your host-address isn’t correct (as already in above answers pointed out). As you probably have a physical device it must access the emulator server you hooked up to your computer (aka your IP adress).

How to get my IP-Adress?

MAC: ifconfig | grep "inet " | grep -Fv 127.0.0.1 | awk '{print $2}'

WINDOWS: netsh interface ip show address | findstr "IP Address"