Sergey's questions

masm64如何使用printf函数在一行中打印不同类型的值？

;подключаем библиотеки
includelib kernel32.lib
;подключаем библиотеку C
includelib msvcrt.lib 
;для совместимости старых функций C
includelib ucrt.lib
;для использования старых функций ввода-вывода
includelib legacy_stdio_definitions.lib
;=====

;подключаем функции
extern ExitProcess: PROC
extern SetConsoleOutputCP: PROC
extern getchar: PROC
extern printf: proc
;=====

.data

 a qword 15
 b qword 255

 ;13 или \r - перевод каретки
 ;10 или \n - перевод строки
 ;0  или \0 - нулевой байт
 ;%d - формат вывода целого числа
 msg byte "%d %d", 13, 10, 0 

.code
main proc
 
 mov rax, 65001
 call SetConsoleOutputCP

 ;аргументы передаются в функцию в обратном порядке
 mov rdx, b
 mov rcx, rdx
 mov rdx, a
 mov rcx, rdx
 mov rcx, offset msg
 call printf
 
 call getchar
 
 mov rax, 0
 call ExitProcess

main endp
end

答案如下

15 -1607011040

无法为 TextField 创建边框颜色和粗细。您可以为输入字段添加边框

TextField(
 decoration: InputDecoration(
  border: OutlineInputBorder(),
 )
),

我想更改边框的颜色和粗细，但由于某种原因没有发生更改

TextField(
 decoration: InputDecoration(
  border: OutlineInputBorder(
   borderSide: BorderSide(
    color: Colors.pink,
    width: 5.0
   ),
  ),
 )
),

下面是完整的代码和截图

主要.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
 const MyApp({Key? key}) : super(key: key);

 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: const Text('Name Page'),
    ),
    body: const SafeArea(
     child: MyHomePage(),
    ),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 const MyHomePage({Key? key}) : super(key: key);

 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 @override
 void initState() {
  super.initState();
 }

 @override
 void dispose() {
  super.dispose();
 }

 @override
 Widget build(BuildContext context) {
  return const Center(
   child: Padding(
    padding: EdgeInsets.symmetric(horizontal: 16.0),
    child: TextField(
     decoration: InputDecoration(
      border: OutlineInputBorder(
       borderSide: BorderSide(
        color: Colors.pink,
        width: 5.0
       ),
      ),
     )
    ),
   ),
  );
 }

}

如果将图像连接到协议为HTTPS的地址，则一切正常。

final String _path = 'https://flutter.github.io/assets-for-api-docs/assets/widgets/owl-2.jpg';

如果您将图像连接到协议为HTTP的地址，那么一切都不起作用。

final String _path = 'http://fr38060s.bget.ru/_html/perform/img/car.jpg';

以前，这个问题是通过这种方式解决的。在文件中，在应用程序 AndroidManifest.xml标记中，添加了该属性

android:usesCleartextTraffic="true"

现在，如果您单击链接，一切都会有所不同

网络安全配置

我在android/app/src/main/res文件夹中创建了xml文件夹

在其中创建了一个network-security-config.xml文件

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
 <base-config cleartextTrafficPermitted="true" />
</network-security-config>

在AndroidManifest.xml添加

android:networkSecurityConfig="@xml/network-security-config"

这是完整的代码

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 package="com.example.f1">

 <application
  android:networkSecurityConfig="@xml/network-security-config"
  android:name="${applicationName}"
  android:icon="@mipmap/ic_launcher"
  android:label="f1">
  <activity
   android:name=".MainActivity"
   android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
   android:exported="true"
   android:hardwareAccelerated="true"
   android:launchMode="singleTop"
   android:theme="@style/LaunchTheme"
   android:windowSoftInputMode="adjustResize">
   <!-- Specifies an Android theme to apply to this Activity as soon as
        the Android process has started. This theme is visible to the user
        while the Flutter UI initializes. After that, this theme continues
        to determine the Window background behind the Flutter UI. -->
   <meta-data
    android:name="io.flutter.embedding.android.NormalTheme"
    android:resource="@style/NormalTheme" />
   <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
   </intent-filter>
  </activity>
  <!-- Don't delete the meta-data below.
       This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
  <meta-data
   android:name="flutterEmbedding"
   android:value="2" />
 </application>
</manifest>

主要.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
 const MyApp({Key? key}) : super(key: key);

 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: const Text('Name Page'),
    ),
    body: const SafeArea(
     child: MyHomePage(),
    ),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 const MyHomePage({Key? key}) : super(key: key);

 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 //работает, потому что https
 //final String _path = 'https://flutter.github.io/assets-for-api-docs/assets/widgets/owl-2.jpg';

 //не работает, потому что http
 final String _path = 'http://fr38060s.bget.ru/_html/perform/img/car.jpg';

 @override
 void initState() {
  super.initState();
 }

 @override
 void dispose() {
  super.dispose();
 }

 @override
 Widget build(BuildContext context) {
  return Align(
   alignment: Alignment.center,
   child: Image.network(
    _path,
    fit: BoxFit.contain,
    width: 300.0,
    height: 400.0,
   ),
  );
 }

}

对于 FittedBox 小部件， fit: BoxFit.fill属性不适用于SOMETHING。BoxFit.fill 应该将子小部件拉伸到父小部件的完整宽度和高度。这就是它在文档中所说的

通过扭曲源的纵横比来填充目标框。

最有趣的是，在没有Null-safety的 Dart 版本中，完全相同的代码可以正常工作。

但这不会发生。为简单起见，我将图像替换为填充容器。下面是完整的代码和截图。

主要.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
 const MyApp({Key? key}) : super(key: key);

 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: const Text('Name Page'),
    ),
    body: const SafeArea(
     child: MyHomePage(),
    ),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 const MyHomePage({Key? key}) : super(key: key);

 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 @override
 void initState() {
  super.initState();
 }

 @override
 void dispose() {
  super.dispose();
 }

 @override
 Widget build(BuildContext context) {
  return Align(
   alignment: Alignment.center,
   child: Container(
    width: 200.0,
    height: 200.0,
    color: Colors.amber,
    alignment: Alignment.center,
    child: FittedBox(
     fit: BoxFit.fill,

     /*child: Image.asset(
      //width = 240, height = 400
      'assets/images/a.jpg',
     ),*/

     child: Container(
      width: 240.0,
      height: 400.0,
      color: Colors.green,
     ),

    ),
   ),
  );
 }

}

动画之间发生错误。一切正常，但红屏出现片刻。下面是完整的代码和截图。

主要.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
 const MyApp({Key? key}) : super(key: key);

 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: const MyHomePage(),
  );
 }
}

class MyHomePage extends StatefulWidget {
 const MyHomePage({Key? key}) : super(key: key);

 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with
 SingleTickerProviderStateMixin {

 String _str = '1';
 bool _b = false;

 Curve? _curve;
 AnimationController? _animationController;
 Animation<Color>? _animateColor;
 Animation<double>? _animateIcon;


 @override
 void initState() {
  super.initState();

  _curve = Curves.easeOut;

  _animationController = AnimationController(
   vsync: this,
   duration: const Duration(milliseconds: 500))
   ..addListener(() {
    setState(() {

    });
   });

  _animateColor = Tween<Color>(
   begin: Colors.green,
   end: Colors.lightBlue,
  ).animate(CurvedAnimation(
   parent: _animationController!,
   curve: Interval(
    0.00,
    1.00,
    curve: _curve!
   ),
  ));

  _animateIcon = Tween<double>(
   begin: 0.0,
   end: 1.0
  ).animate(_animationController!);

 }

 @override
 void dispose() {
  super.dispose();
  _animationController!.dispose();
 }

 void _f1() {
  setState(() {
   if (_b) {
    _str = '1';
    _b = false;
    _animationController!.reverse();
   } else {
    _str = '2';
    _b = true;
    _animationController!.forward();
   }
  });
 }

 @override
 Widget build(BuildContext context) {
  return Scaffold(
   appBar: AppBar(
    title: const Text('Name Page'),
   ),
   body:  SafeArea(
    child: Center(
     child: Text(
      _str,
      style: const TextStyle(
       fontSize: 36.0,
       color: Colors.pink
      ),
     ),
    ),
   ),

   //кнопка
   floatingActionButton: FloatingActionButton(
    onPressed: () { _f1(); },
    child: AnimatedIcon(
     icon: AnimatedIcons.menu_close,
     progress: _animateIcon!,
    ),
    backgroundColor: _animateColor!.value,
    foregroundColor: Colors.white,
   ),

   //расположение кнопки
   floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,

   //бар находится только внизу
   bottomNavigationBar: BottomAppBar(
    child: Container(
     height: 50.0,
    ),
    color: Colors.amber,
    shape: const CircularNotchedRectangle(),
    notchMargin: 8.0,
   ),

  );
 }

}

现在如何删除状态栏？以前是这样完成的：

SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.bottom]);

现在不推荐使用setEnabledSystemUIOverlays()方法。

@Deprecated('迁移到 setEnabledSystemUIMode。' '此功能在 v2.3.0-17.0.pre 之后被弃用。')

告诉我现在（SDK Flutter 2.5.3）如何移除 StatusBar？

如何将 Set 集合转换为 Map 集合？在此示例中，我已将 Set 转换为 List，然后再转换为 Map。但也许有更优雅的方式？

主要.dart

void main() {
 Set ara1 = {'H', 'e', 'l', 'o'};
 Map ara2 = ara1.toList().asMap();

 for(var i in ara2.entries) {
  print('${i.key} : ${i.value}');
 }

 print('');

 ara2.forEach((k, v) {
  print('$k : $v');
 });

 print('\n${ara2.runtimeType}');
}

回答

0 : H
1 : e
2 : l
3 : o

0 : H
1 : e
2 : l
3 : o

ListMapView<dynamic>

如何正确声明一个非固定列表类型的列表，如变体 1 或变体 2 中的，或者两者都是正确的？编译器不会抛出任何错误。

void main() {
 //1 вариант
 List ara1 = <int>[];
 //2 вариант
 List<int> ara2 = [];
 
 print(ara1.runtimeType); //List<int>
 print(ara2.runtimeType); //List<int>
}

错误描述
======== 小部件库捕获的异常 在
构建 MyHomePage(dirty, state: _MyHomePageState#ef271) 时引发了以下 NoSuchMethodError：
在 null 上调用了 getter 'value'。
接收者：空
尝试调用：值

相关的导致错误的小部件是：MyHomePage file:///D:/project/flutter/f1/lib/main.dart:20:
11
#0 Object.noSuchMethod (dart:core-patch /object_patch.dart:51:5)
#1 _MyHomePageState.build (package:f1/main.dart:80:25)
#2 StatefulElement.build (package:flutter/src/widgets/framework.dart:4744:28)
# 3 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4627:15)
#4 StatefulElement.performRebuild(package:flutter/src/widgets/framework.dart:4800:11)

出现红色错误屏幕一秒钟，然后一切正常

此外， main.dart的完整代码

import 'package:flutter/material.dart';

import 'package:camera/camera.dart';

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

class MyApp extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: Text('Name Page'),
    ),
    body: MyHomePage(),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 CameraController _cameraController;

 @override
 void initState() {
  super.initState();
  _funInitialization();

 }

 @override
 void dispose() {
  super.dispose();
  _cameraController.dispose();

 }

 void _f1() {
  setState(() {

  });
 }

 Future<void> _funInitialization() async {

  List<CameraDescription> cameras = await availableCameras();

  _cameraController = CameraController(
   cameras[0],
   ResolutionPreset.max
  )..initialize().then((_) {
   if (!mounted) {
    return;
   }
   setState(() {});
  });

 }

 @override
 Widget build(BuildContext context) {

  if(!_cameraController.value.isInitialized) {
   return Container();
  }

  return Stack(
   children: [
    Align(
     alignment: Alignment.center,
     /*child: AspectRatio(
      aspectRatio: 3 / 4,
      child: CameraPreview(_cameraController),
     ),*/
     child: Container(
      width: MediaQuery.of(context).size.width,
      child: CameraPreview(_cameraController),
     ),
    ),
   ],
  );

 }

}

当您启动应用程序时，中心的铭文 Hello World!。单击“检查”按钮后，理论上应该会出现一条关于 Internet 连接或不存在的消息。什么都没发生。为什么？下面是完整的代码和截图。

主要.dart

import 'package:flutter/material.dart';

import 'package:connectivity/connectivity.dart';

import 'dart:async';

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

class MyApp extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: Text('Name Page'),
    ),
    body: MyHomePage(),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 String _str = 'Hello World!';

 @override
 void initState() {
  super.initState();

 }

 @override
 void dispose() {
  super.dispose();

 }

 void _f1() {
  setState(() {

  });
 }

 Future<void> _funCheckInternetConnection() async {

  ConnectivityResult result = await Connectivity().checkConnectivity();

  if(result == ConnectivityResult.mobile) {
   setState(() {
    _str = 'connected to a mobile network';
   });
  } else if(result == ConnectivityResult.wifi) {
   setState(() {
    _str = 'connected to a wifi network';
   });
  } else if(result == ConnectivityResult.none) {
   setState(() {
    _str = 'disconnected to a network';
   });
  }

 }

 @override
 Widget build(BuildContext context) {
  return Stack(
   children: [
    Align(
     alignment: Alignment.topCenter,
     child: TextButton(
      onPressed: () { _funCheckInternetConnection(); },
      child: Container(
       width: 100.0,
       height: 50.0,
       decoration: BoxDecoration(
        color: Colors.black12,
        borderRadius: BorderRadius.all(
         Radius.circular(10.0)
        )
       ),
       alignment: Alignment.center,
       child: Text(
        'Check',
        style: TextStyle(
         fontSize: 20,
         color: Colors.deepPurpleAccent
        ),
       ),
      ),
     ),
    ),
    Align(
     alignment: Alignment.center,
     child: Text(
      _str,
      style: TextStyle(
       fontSize: 26.0,
       color: Colors.pink
      ),
     ),
    ),
   ],
  );
 }

}

Canvas 类的clipPath 方法不裁剪指定区域。一个正方形被绘制成蓝色。clipPath 方法应该将它剪辑成一个三角形。它没有发生。告诉。下面是完整的代码和截图。

主要.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: Text('Name Page'),
    ),
    body: MyHomePage(),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 @override
 void initState() {
  super.initState();

 }

 @override
 void dispose() {
  super.dispose();

 }

 void _f1() {
  setState(() {

  });
 }

 @override
 Widget build(BuildContext context) {
  return Stack(
   children: [
    Align(
     alignment: Alignment.center,
     child: CustomPaint(
      //верхний слой
      foregroundPainter: A(),
      //средний слой
      child: Container(
       width: 300.0,
       height: 300.0,
       decoration: BoxDecoration(
        border: Border.all(
         width: 1.0,
         color: Colors.pink
        ),
       ),
      ),
     ),
    ),
   ],
  );
 }

}

class A extends CustomPainter {

 @override
 void paint(Canvas canvas, Size size) {

  //синий цвет, заполнение
  final paint = Paint()
   ..style = PaintingStyle.fill
   ..color = Colors.blue;

  //квадрат
  canvas.drawRRect(
   RRect.fromRectAndRadius(
    Rect.fromLTWH(0, 0, 250, 250),
    Radius.circular(0)
   ),
   paint,
  );

  //область треугольника, которая должна обрезаться
  canvas.clipPath(
   Path()
    ..lineTo(0.0, 0.0)
    ..lineTo(0, size.height - 50)
    ..lineTo(size.width - 50, size.height - 50)
    ..close()
  );

 }

 @override
 bool shouldRepaint(covariant CustomPainter oldDelegate) {
  return false;
 }

}

在哪里放置一个函数来填充表中的数据？函数定义

/*ФУНКЦИЯ ЗАПОЛНЯЕТ КОЛЛЕКЦИЮ ДАННЫМИ ИЗ ТАБЛИЦЫ*/
 Future<void> _funGetData() async {
  var list = await _database.rawQuery('SELECT * FROM Person');
  //заполняем коллекцию объектами
  _ara = List<Person>.from( list.map((e) => Person.fromMap(e)) );
 }

函数调用

//ГДЕ НУЖНО РАЗМЕСТИТЬ ЭТУ ФУНКЦИЮ ???
_funGetData();

在我的示例中，该函数位于数据库创建或初始化之后，检查之后。我应该在哪里正确放置？？？

if(_database.isOpen) {
   _funTableCreate(_tablePerson);
   //ГДЕ НУЖНО РАЗМЕСТИТЬ ЭТУ ФУНКЦИЮ ???
   _funGetData();
  }

然后出现表中的数据输出。一个非常简单的选择。

此外，1个简单变体的完整代码。 主要.dart

import 'package:flutter/material.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:ext_storage/ext_storage.dart';

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

class MyApp extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: Text('Name Page'),
    ),
    body: MyHomePage(),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 String _str1 = '';
 String _str2 = '';

 Database _database;
 String _databasesPath = '';
 String _databaseName = '';

 String _tablePerson = '''
  CREATE TABLE Person(
   id INTEGER NOT NULL,
   name TEXT NOT NULL,
   age INTEGER NOT NULL
  )
 ''';

 List<Person> _ara = [];

 @override
 void initState() {
  super.initState();
  _funDatabaseInit();

 }

 Future<void> _funDatabaseInit() async {
  //путь к расположению базы данных
  _databasesPath = await ExtStorage.getExternalStoragePublicDirectory(ExtStorage.DIRECTORY_DOWNLOADS);
  //имя базы данных
  _databaseName = 'abc.db';
  //соединение пути и имени
  String pathAll = join(_databasesPath, _databaseName);
  //создание или открытие базы
  _database = await openDatabase(pathAll);

  if(_database.isOpen) {
   _funTableCreate(_tablePerson);
   //ГДЕ НУЖНО РАЗМЕСТИТЬ ЭТУ ФУНКЦИЮ ???
   _funGetData();
  }

  setState(() {
   _str1 = '';
   _str2 = '';
   _str1 = '${_database.isOpen}';
   _str2 = _database.path;
  });

 }

 /**/
 Future<void> _funTableCreate(String table) async {
  await _database.execute(table);
 }

 /**/
 Future<void> _funTableInsert(String table, dynamic classModel) async {
  await _database.insert(
   table,
   classModel.toMap(),
   conflictAlgorithm: ConflictAlgorithm.replace
  );
 }

 /*ФУНКЦИЯ ЗАПОЛНЯЕТ КОЛЛЕКЦИЮ ДАННЫМИ ИЗ ТАБЛИЦЫ*/
 Future<void> _funGetData() async {
  var list = await _database.rawQuery('SELECT * FROM Person');
  //заполняем коллекцию объектами
  _ara = List<Person>.from( list.map((e) => Person.fromMap(e)) );
 }

 @override
 Widget build(BuildContext context) {
  return Column(
   children: [
    Padding(
     padding: const EdgeInsets.all(8.0),
     child: Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: [
       OutlineButton(
        onPressed: () {
         setState(() {
          _funTableInsert(
           'Person',
           Person(id: 1, name: 'Ivan', age: 21)
          );
         });
        },
        child: Text(
         'Insert',
         style: TextStyle(
          fontSize: 20.0,
          color: Colors.deepPurple
         ),
        ),
       ),
      ],
     ),
    ),
    Padding(
     padding: const EdgeInsets.all(8.0),
     child: Row(
      children: [
       Text(
        'database is open : $_str1'
       ),
      ],
     ),
    ),
    Padding(
     padding: const EdgeInsets.all(8.0),
     child: Row(
      children: [
       Text(
        'path : $_str2'
       ),
      ],
     ),
    ),

    Padding(
     padding: const EdgeInsets.all(8.0),
     child: Row(
      children: [
       Text(
        '${_ara[0].id} ${_ara[0].name} ${_ara[0].age} ',
       ),
      ],
     ),
    ),

   ],
  );
 }

}

class Person {

 //название столбцов таблицы должно совпадать с названием полей
 final int id;
 final String name;
 final int age;

 Person({
  this.id,
  this.name,
  this.age
 });

 //для вставки данных в таблицу
 Map<String, dynamic> toMap() {
  return {
   'id': id,
   'name': name,
   'age': age,
  };
 }

 //для чтения данных из таблицы
 factory Person.fromMap(Map<String, dynamic> map) => Person(
  id: map['id'] as int,
  name: map['name'] as String,
  age: map['age'] as int
 );

}

在第二个变体中，任务稍微复杂一些。创建了一个小部件，条件是如果集合的长度为 0，则铭文 Hello World！，如果不等于0，则显示表格数据。Hello World 出现了一会儿！，也就是说，由于某种原因，数据尚未加载到集合中。

然后你好世界！消失，但什么也没有显示。数据应该已经加载。

函数应该放在哪里？下面是第二版
main.dart的完整代码

import 'package:flutter/material.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:ext_storage/ext_storage.dart';

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

class MyApp extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: Text('Name Page'),
    ),
    body: MyHomePage(),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 String _str1 = '';
 String _str2 = '';

 Database _database;
 String _databasesPath = '';
 String _databaseName = '';

 String _tablePerson = '''
  CREATE TABLE Person(
   id INTEGER NOT NULL,
   name TEXT NOT NULL,
   age INTEGER NOT NULL
  )
 ''';

 List<Person> _ara = [];

 @override
 void initState() {
  super.initState();
  _funDatabaseInit();

 }

 Future<void> _funDatabaseInit() async {
  //путь к расположению базы данных
  _databasesPath = await ExtStorage.getExternalStoragePublicDirectory(ExtStorage.DIRECTORY_DOWNLOADS);
  //имя базы данных
  _databaseName = 'abc.db';
  //соединение пути и имени
  String pathAll = join(_databasesPath, _databaseName);
  //создание или открытие базы
  _database = await openDatabase(pathAll);

  if(_database.isOpen) {
   _funTableCreate(_tablePerson);
   //ГДЕ НУЖНО РАЗМЕСТИТЬ ЭТУ ФУНКЦИЮ ???
   _funGetData();
  }

  setState(() {
   _str1 = '';
   _str2 = '';
   _str1 = '${_database.isOpen}';
   _str2 = _database.path;
  });

 }

 /**/
 Future<void> _funTableCreate(String table) async {
  await _database.execute(table);
 }

 /**/
 Future<void> _funTableInsert(String table, dynamic classModel) async {
  await _database.insert(
   table,
   classModel.toMap(),
   conflictAlgorithm: ConflictAlgorithm.replace
  );
 }

 /*ФУНКЦИЯ ЗАПОЛНЯЕТ КОЛЛЕКЦИЮ ДАННЫМИ ИЗ ТАБЛИЦЫ*/
 Future<void> _funGetData() async {
  var list = await _database.rawQuery('SELECT * FROM Person');
  //заполняем коллекцию объектами
  _ara = List<Person>.from( list.map((e) => Person.fromMap(e)) );
 }

 Widget _widgetW() {
  if(_ara.length == 0) {
   return Padding(
    padding: const EdgeInsets.all(8.0),
    child: Row(
     children: [
      Text(
       'Hello World!',
       style: TextStyle(
        fontSize: 24.0,
        color: Colors.pink,
       ),
      )
     ],
    ),
   );
  } else {
   return Padding(
    padding: const EdgeInsets.all(8.0),
    child: Row(
     children: [
      ListView.builder(
       itemCount: _ara.length,
       itemBuilder: (context, index) {
        return Text(
         '${_ara[index].id} ${_ara[index].name} ${_ara[index].age} ',
        );
       },
      ),
     ],
    ),
   );
  }
 }

 @override
 Widget build(BuildContext context) {
  return Column(
   children: [
    Padding(
     padding: const EdgeInsets.all(8.0),
     child: Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: [
       OutlineButton(
        onPressed: () {
         setState(() {
          _funTableInsert(
           'Person',
           Person(id: 1, name: 'Ivan', age: 21)
          );
         });
        },
        child: Text(
         'Insert',
         style: TextStyle(
          fontSize: 20.0,
          color: Colors.deepPurple
         ),
        ),
       ),
      ],
     ),
    ),
    Padding(
     padding: const EdgeInsets.all(8.0),
     child: Row(
      children: [
       Text(
        'database is open : $_str1'
       ),
      ],
     ),
    ),
    Padding(
     padding: const EdgeInsets.all(8.0),
     child: Row(
      children: [
       Text(
        'path : $_str2'
       ),
      ],
     ),
    ),

    _widgetW(),

   ],
  );
 }

}

class Person {

 //название столбцов таблицы должно совпадать с названием полей
 final int id;
 final String name;
 final int age;

 Person({
  this.id,
  this.name,
  this.age
 });

 //для вставки данных в таблицу
 Map<String, dynamic> toMap() {
  return {
   'id': id,
   'name': name,
   'age': age,
  };
 }

 //для чтения данных из таблицы
 factory Person.fromMap(Map<String, dynamic> map) => Person(
  id: map['id'] as int,
  name: map['name'] as String,
  age: map['age'] as int
 );

}