fetching data from api and pass it to next page but showing error

//sign() fnction is in statless widget 
var y
y=signIn(); 
 Navigator.of(context).push(
                         MaterialPageRoute(
                           builder: (context) =>  posting(y),
                         ),
                       );

Future<Response?> signIn() async {
  var dio = Dio();
  try {
    var response = await dio.post('https://cisfapp.cisf.gov.in/abc/post.php',
        data: {
          "method"  : "posting",
          "username" : 1652356789
        },
        options: Options(
            headers: {
              'Content-Type': 'application/json',
              'Accept': 'application/json'
            }
        ));
    Map mapResponse = {};
    mapResponse = jsonDecode(response.data);
    var x = mapResponse['data'][2]['unit_name'];
    print(x); //want to pass the value of x to next page 

    return response;
  } catch (e) {
    print(e.toString());
  }
  return null;
}

this is the output of above program which is properly working according to me

please check in image,it is showing Instance of 'Future<Response<dynamic>?>

api output is :-
{
"message":"success",
"err-code":"0",
"data":
[
{
"unit_name":"alpha",
"from_date":"2010-04-01 00:00:00",
"sector_name":"TRG"
},
{
"unit_name":"Bravo",
"from_date":"2018-03-10 00:00:00",
"sector_name":"Eastern"
},
{
"unit_name":"charlie",
"from_date":"2020-05-09 00:00:00",
"sector_name":"western"
}
]

}
i want the specific value of unit_name which is "charlie" and which is at index [2] of output api......help pls if anyone can

Use await keyword for wait for response from API.

    var y
    y.then(result => {
       Navigator.of(context).push(MaterialPageRoute(
            builder: (context) => posting(result),),);
      }).catch(error => {
    });


Future<String?> signIn() async {
    var dio = Dio();
    try {
      var response = await dio.post('https://cisfapp.cisf.gov.in/abc/post.php',
          data: {
            "method" : "posting",
            "username" : 1652356789
          },
          options: Options(
              headers: {
                'Content-Type': 'application/json',
                'Accept': 'application/json'
              }
          ));
      Map mapResponse = response.data as Map<dynamic, dynamic>;
      return mapResponse['data'][2]['unit_name'];
    } catch (e) {
      print(e.toString());
    }
    return null;
  }

The error may be because signIn() returns a Future<String?> but you are trying to pass the result of the future (which is a String?) to the posting constructor. Instead, you should wait for the future to complete and then pass the result to the constructor. You can do this using the await keyword. Here's an example:

var response = await signIn(); // wait for signIn() to complete and get the response
Navigator.of(context).push(
  MaterialPageRoute(
    builder: (context) => posting(response), // pass the response data to the constructor
  ),
);

  Future<String?> signIn() async {
var dio = Dio();
try {
  var response = await dio.post('https://cisfapp.cisf.gov.in/abc/post.php',
      data: {"method": "posting", "username": 1652356789},
      options: Options(headers: {
        'Content-Type': 'application/json',
        'Accept': 'application/json'
      }));
  Map mapResponse = {};
  mapResponse = jsonDecode(response.data);
  var x = mapResponse['data'][2]['unit_name'];
  return x;
} catch (e) {
  print(e.toString());
}
return null;

}

Also, make sure that you are handling errors properly. If there is an error while fetching data from the API, signIn() will return null. You should handle this case and show an appropriate error message to the user.

You can try this, or simply using await

var y;
y = signIn();
y.then(result => {
    Navigator.of(context).push(
        MaterialPageRoute(
            builder: (context) => posting(result),),);

}).catch(error => {
});