Flutter: How to call a Future http.Post from my Login button - flutter

Question

So far I have created my app with the pages I need and a login screen. At the moment the login screen just simply opens the first page in the app when the login button is touched (no authentication is done). I have written a small test app to get the login with http authentication working. Now I need to move the working authentication code into my app, but I'm not sure how to call the Future from the login button.
the Future is as follows: (just running local at the moment)
Future<Staff> fetchStaff() async {
final response = await http.post(
Uri.encodeFull('http://10.0.2.2:8080/modules/rmo_daMLogin'),
headers: {'Content-Type': 'text/plain'},
body: 'rmoService=User_Login\n'
'UserId=fred\n'
'Password=abc123');
if (response.statusCode == 200) {
// If the server did return a 200 OK response, then parse the JSON.
return Staff.fromJson(json.decode(response.body));
} else {
// If the server did not return a 200 OK response, then throw an exception.
throw Exception('User or Password was incorrect.');
}
}
Staff is defined as a class and just contains all the fields returned by the web service.
My login page contains the following. How do I call the Future from the Login button press and if Staff data is returned ok, how do I then use the pushReplacement of the Navigator to change pages?
Thanks for any help,
Paul
class RmoLogin extends StatelessWidget {
final TextStyle style = TextStyle(fontFamily: 'Montserrat', fontSize: 20.0);
TextEditingController usernameController = new TextEditingController();
TextEditingController passwordController = new TextEditingController();
Future<Staff> futureStaff;
#override
Widget build(BuildContext context) {
final futureStaff = fetchStaff();
final userField = TextField(
obscureText: false,
style: style,
controller: usernameController,
decoration: InputDecoration(
contentPadding: EdgeInsets.fromLTRB(20.0, 15.0, 20.0, 15.0),
hintText: "User Name",
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(12.0),
),
),
);
final passwordField = TextField(
obscureText: true,
style: style,
controller: passwordController,
decoration: InputDecoration(
contentPadding: EdgeInsets.fromLTRB(20.0, 15.0, 20.0, 15.0),
hintText: "Password",
border:
OutlineInputBorder(borderRadius: BorderRadius.circular(12.0))),
);
final loginButton = Material(
elevation: 5.0,
borderRadius: BorderRadius.circular(12.0),
color: Color(0xff01A0C7),
child: MaterialButton(
minWidth: MediaQuery.of(context).size.width,
padding: EdgeInsets.fromLTRB(20.0, 15.0, 20.0, 15.0),
child: Text(
"Login",
textAlign: TextAlign.center,
style:
style.copyWith(color: Colors.white, fontWeight: FontWeight.bold),
),
onPressed: () {
Navigator.of(context).pushReplacement(
MaterialPageRoute(
builder: (BuildContext context) => MyJobsPage(),
),
);
},
),
);
return Scaffold(
appBar: AppBar(
centerTitle: true,
backgroundColor: Color(0xff01A0C7),
title: Column(children: [
Text('Jobs Organiser'),
Text('Login', style: TextStyle(fontSize: 14)),
]),
),
body: Container(
color: Colors.white,
child: Padding(
padding: const EdgeInsets.fromLTRB(36, 20, 36, 36),
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
SizedBox(
height: 75.0,
child: Image.asset(
"assets/Users.png",
fit: BoxFit.contain,
),
),
SizedBox(height: 45.0),
userField,
SizedBox(height: 25.0),
passwordField,
SizedBox(height: 35.0),
loginButton,
SizedBox(height: 15.0),
],
),
),
),
);
}
}