flutter async call doesn't run asynchronously in initState() - flutter

Question

I'm calling async function in initState(),
but the system actually waits the result of async function.
Could anyone tell me why?
Here's my code:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(home: MyHomePage());
}
}
class MyHomePage extends StatefulWidget {
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
Future<int> _f;
#override
void initState() {
super.initState();
Stopwatch stopwatch = new Stopwatch()..start();
print('executed in ${stopwatch.elapsed}');
_f = getFuture();
print('executed in ${stopwatch.elapsed}');
}
Future<int> getFuture() async {
int i = 0;
while(i < 1000000000) {
i++;
}
return i;
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text("test")),
body: FutureBuilder<int>(
future: _f,
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.done:
return Center(child: Text("snapshot: ${snapshot.data}"));
break;
default:
return Center(child: CircularProgressIndicator());
}
}
),
);
}
}
And here's the output:
I/flutter (22058): executed in 0:00:00.000384
I/flutter (22058): executed in 0:00:04.536278

Answer 1

A Future function is made to return a Future object asynchronously. Which means executing a statement of code once that will take a much longer time, for example getting json object from an api, than the usual time required for a normal statement, for example a declaration of a variable.
However, you are executing a normal statement, that requires milliseconds to run, a 1000000000 times. That will result in a longer execution time which was built up by the milliseconds of each execution.
Even though it is a Future function, it is not returning a Future object or variable, so it is not asynchronous.