Flutter - redirect to new screen using .then(), Provider.of(), and Navigator

Question

I have a button which on initial click/tap/touch, it POST to API and return true or false based on auth.

onPressed: ()=>{
Provider.of<Login>(context, listen: false).login()
.then((value) => {
  if(value == true)
    Navigator.pushReplacementNamed(context, '/home')
  }),
},

Future<bool> login() async {
    try{
      var payload = jsonEncode({
        'email': usrname,
        'password': pswd
      });
      Map<String,dynamic> response = await fetch.post(url, body:payload, headers: {
        'Accept':'application/json',
        'content-type': 'application/json'
      })
      .then((value) => jsonDecode(value.body));
      if(response['token'] != ''){
        return true;
      }
    }
    catch(e){
      errorMsg = e.toString();
      notifyListeners();
      return false;
    }
    return false;
  }

On successful authentication, it doesn't redirect to new screen as intended. Am I missing something or my logic is flawed?

score 1 · Accepted Answer · answered Apr 05 '22 at 06:16

await is meant to interrupt the process flow until the async method has finished. then however does not interrupt the process flow (meaning the next instructions will be executed) but enables you to run code when the async method is finished.

In your code :

The issue is about your login method. You used an await with a then, you don't need to use both at the same time.

Future<bool> login() async {
    try{
      var payload = jsonEncode({
        'email': usrname,
        'password': pswd
      });
      Map<String,dynamic> response = await fetch.post(url, body:payload, headers: {
        'Accept':'application/json',
        'content-type': 'application/json'
      });
      var decodedResponse = jsonDecode(response.body);
      if(decodedResponse['token'] != ''){
        return true;
      }
    }
    catch(e){
      errorMsg = e.toString();
      notifyListeners();
      return false;
    }
    return false;
  }

You can find more examples in SO issues :

This is the ticket! I guess habit from Javascript isn't that easily being forgotten. Thanks a lot! — mitchiri_neko, Apr 05 '22 at 06:26

Flutter - redirect to new screen using .then(), Provider.of(), and Navigator

1 Answers1