PiN73

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

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

PiN73

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp();

PiN73

By default, <ItemsControl>/<ScrollViewer> doesn't use virtualization. All its items are rendered at once. This causes lags/freezing on first render and each re-render (for example, if list data or window size changes).

Adding ScrollViewer.CanContentScroll="True" will enable virtualization and make loading fast. But the list will be scrolled one whole item a time, which feels like jumping if items height is big enough.

To make virtualization enabled and keep smooth scrolling, add also VirtualizingPanel.ScrollUnit="Pixel"

PiN73

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(

PiN73

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(

PiN73

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(

PiN73

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(

PiN73

import 'package:flutter/foundation.dart';

extension NumExtension on num {
  bool greaterThan(num other) => this > other;
}

class MyClass {
  final bool a;
  final bool b;
  final bool c;

PiN73

void main() {
  Map<int, MapEntry<String, String>> m = {};
  m[5] = MapEntry("five", "5");
  print(m);
}

PiN73

C:\Users\Pavel\AndroidStudioProjects\test_functional_widget>flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, v1.9.1+hotfix.6, on Microsoft Windows [Version 10.0.18362.418], locale ru-RU)

[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
[√] Android Studio (version 3.5)
[√] Connected device (1 available)

• No issues found!