Flutter Frame Rate

main.dart

import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';

void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    SchedulerBinding.instance.addPersistentFrameCallback(_frame);
    super.initState();
  }

  int _lastFrameTime = 0;
  String _frameRate = "0 fps";
  void _frame(Duration elapsed) {
    int elapsedMicroseconds = elapsed.inMicroseconds;
    double elapsedSeconds = (elapsedMicroseconds - _lastFrameTime) * 1e-6;
    if (elapsedSeconds != 0) {
      _lastFrameTime = elapsedMicroseconds;
      setState(() {
        _frameRate = '${(1.0 / elapsedSeconds).round()} fps';
      });
    }
    // Redraw.
    SchedulerBinding.instance.scheduleFrame();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Material(
        child: Container(
          child: Center(
            child: Text(_frameRate),
          ),
        ),
      ),
    );
  }
}