Flutter - 开发高级应用

在本章中，我们将学习如何编写一个完整的移动应用程序，expense_calculator。expense_calculator 的目的是存储我们的支出信息。应用程序的完整功能如下：

支出列表。
输入新支出的表单。
编辑/删除现有支出的选项。
任何时候的总支出。

我们将使用 Flutter 框架下面提到的高级功能来编写 expense_calculator 应用程序。

高级 ListView 用法来显示支出列表。
表单编程。
SQLite 数据库编程来存储我们的支出。
scoped_model 状态管理来简化我们的编程。

让我们开始编写expense_calculator应用程序。

在 Android Studio 中创建一个新的 Flutter 应用程序，expense_calculator。
打开 pubspec.yaml 并添加包依赖项。

dependencies: 
   flutter: 
      sdk: flutter 
   sqflite: ^1.1.0 
   path_provider: ^0.5.0+1 
   scoped_model: ^1.0.1 
   intl: any

请注意以下几点：

sqflite 用于 SQLite 数据库编程。
path_provider 用于获取特定于系统的应用程序路径。
scoped_model 用于状态管理。
intl 用于日期格式化。

Android Studio 将显示以下警报，提示 pubspec.yaml 已更新。

点击“获取依赖项”选项。Android Studio 将从互联网获取包并为应用程序正确配置它。
删除 main.dart 中的现有代码。
添加新文件 Expense.dart 以创建 Expense 类。Expense 类将具有以下属性和方法。

属性：id - 在 SQLite 数据库中表示支出条目的唯一 ID。
属性：amount - 支出的金额。
属性：date - 支出日期。
属性：category - 类别表示支出领域，例如食物、旅行等。
formattedDate - 用于格式化 date 属性
fromMap - 用于将数据库表中的字段映射到支出对象中的属性，并创建新的支出对象。

factory Expense.fromMap(Map<String, dynamic> data) { 
   return Expense( 
      data['id'], 
      data['amount'], 
      DateTime.parse(data['date']),    
      data['category'] 
   ); 
}

toMap - 用于将支出对象转换为 Dart Map，这可以进一步用于数据库编程

Map<String, dynamic> toMap() => { 
   "id" : id, 
   "amount" : amount, 
   "date" : date.toString(), 
   "category" : category, 
};

columns - 静态变量，用于表示数据库字段。

将以下代码输入 Expense.dart 文件并保存。

import 'package:intl/intl.dart'; class Expense {
   final int id; 
   final double amount; 
   final DateTime date; 
   final String category; 
   String get formattedDate { 
      var formatter = new DateFormat('yyyy-MM-dd'); 
      return formatter.format(this.date); 
   } 
   static final columns = ['id', 'amount', 'date', 'category'];
   Expense(this.id, this.amount, this.date, this.category); 
   factory Expense.fromMap(Map<String, dynamic> data) { 
      return Expense( 
         data['id'], 
         data['amount'], 
         DateTime.parse(data['date']), data['category'] 
      ); 
   }
   Map<String, dynamic> toMap() => {
      "id" : id, 
      "amount" : amount, 
      "date" : date.toString(), 
      "category" : category, 
   }; 
}

以上代码简单易懂。
添加新文件 Database.dart 以创建 SQLiteDbProvider 类。SQLiteDbProvider 类的目的是：

使用 getAllExpenses 方法获取数据库中所有可用的支出。它将用于列出所有用户的支出信息。

Future<List<Expense>> getAllExpenses() async { 
   final db = await database; 
   
   List<Map> results = await db.query(
      "Expense", columns: Expense.columns, orderBy: "date DESC"
   );
   List<Expense> expenses = new List(); 
   results.forEach((result) {
      Expense expense = Expense.fromMap(result); 
      expenses.add(expense); 
   }); 
   return expenses; 
}

使用 getExpenseById 方法根据数据库中可用的支出标识获取特定支出信息。它将用于向用户显示特定的支出信息。

Future<Expense> getExpenseById(int id) async {
   final db = await database;
   var result = await db.query("Expense", where: "id = ", whereArgs: [id]);
   
   return result.isNotEmpty ? 
   Expense.fromMap(result.first) : Null; 
}

使用 getTotalExpense 方法获取用户的总支出。它将用于向用户显示当前的总支出。

Future<double> getTotalExpense() async {
   final db = await database; 
   List<Map> list = await db.rawQuery(
      "Select SUM(amount) as amount from expense"
   );
   return list.isNotEmpty ? list[0]["amount"] : Null; 
}

使用 insert 方法将新的支出信息添加到数据库中。它将用于用户在应用程序中添加新的支出条目。

Future<Expense> insert(Expense expense) async { 
   final db = await database; 
   var maxIdResult = await db.rawQuery(
      "SELECT MAX(id)+1 as last_inserted_id FROM Expense"
   );
   var id = maxIdResult.first["last_inserted_id"]; 
   var result = await db.rawInsert(
      "INSERT Into Expense (id, amount, date, category)" 
      " VALUES (?, ?, ?, ?)", [
         id, expense.amount, expense.date.toString(), expense.category
      ]
   ); 
   return Expense(id, expense.amount, expense.date, expense.category); 
}

使用 update 方法更新现有支出信息。它将用于用户编辑和更新系统中可用的现有支出条目。

update(Expense product) async {
   final db = await database; 
   
   var result = await db.update("Expense", product.toMap(), 
   where: "id = ?", whereArgs: [product.id]); 
   return result; 
}

使用 delete 方法删除现有支出信息。它将用于用户删除系统中可用的现有支出条目。

delete(int id) async {
   final db = await database;
   db.delete("Expense", where: "id = ?", whereArgs: [id]); 
}

SQLiteDbProvider 类的完整代码如下：

import 'dart:async'; 
import 'dart:io'; 
import 'package:path/path.dart'; 
import 'package:path_provider/path_provider.dart'; 
import 'package:sqflite/sqflite.dart'; 
import 'Expense.dart'; 

class SQLiteDbProvider {
   SQLiteDbProvider._(); 
   static final SQLiteDbProvider db = SQLiteDbProvider._(); 
   
   static Database _database; Future<Database> get database async { 
      if (_database != null) 
         return _database; 
      _database = await initDB(); 
      return _database; 
   } 
   initDB() async {
      Directory documentsDirectory = await getApplicationDocumentsDirectory(); 
      String path = join(documentsDirectory.path, "ExpenseDB2.db"); 
      return await openDatabase(
         path, version: 1, onOpen:(db){}, onCreate: (Database db, int version) async {
            await db.execute(
               "CREATE TABLE Expense (
                  ""id INTEGER PRIMARY KEY," "amount REAL," "date TEXT," "category TEXT""
               )
            "); 
            await db.execute(
               "INSERT INTO Expense ('id', 'amount', 'date', 'category') 
               values (?, ?, ?, ?)",[1, 1000, '2019-04-01 10:00:00', "Food"]
            );
            /*await db.execute(
               "INSERT INTO Product ('id', 'name', 'description', 'price', 'image') 
               values (?, ?, ?, ?, ?)", [
                  2, "Pixel", "Pixel is the most feature phone ever", 800, "pixel.png"
               ]
            ); 
            await db.execute(
               "INSERT INTO Product ('id', 'name', 'description', 'price', 'image') 
               values (?, ?, ?, ?, ?)", [
                  3, "Laptop", "Laptop is most productive development tool", 2000, "laptop.png"
               ]
            );
            await db.execute(
               "INSERT INTO Product ('id', 'name', 'description', 'price', 'image') 
               values (?, ?, ?, ?, ?)", [
                  4, "Tablet", "Laptop is most productive development tool", 1500, "tablet.png"
               ]
            );
            await db.execute(
               "INSERT INTO Product ('id', 'name', 'description', 'price', 'image') 
               values (?, ?, ?, ?, ?)", [
                  5, "Pendrive", "iPhone is the stylist phone ever", 100, "pendrive.png"
               ]
            ); 
            await db.execute(
               "INSERT INTO Product ('id', 'name', 'description', 'price', 'image') 
               values (?, ?, ?, ?, ?)", [
                  6, "Floppy Drive", "iPhone is the stylist phone ever", 20, "floppy.png"
               ]
            ); */ 
         }
      );
   }
   Future<List<Expense>> getAllExpenses() async {
      final db = await database; 
      List<Map> 
      results = await db.query(
         "Expense", columns: Expense.columns, orderBy: "date DESC"
      );
      List<Expense> expenses = new List(); 
      results.forEach((result) {
         Expense expense = Expense.fromMap(result);
         expenses.add(expense);
      }); 
      return expenses; 
   } 
   Future<Expense> getExpenseById(int id) async {
      final db = await database;
      var result = await db.query("Expense", where: "id = ", whereArgs: [id]); 
      return result.isNotEmpty ? Expense.fromMap(result.first) : Null; 
   }
   Future<double> getTotalExpense() async {
      final db = await database;
      List<Map> list = await db.rawQuery(
         "Select SUM(amount) as amount from expense"
      );
      return list.isNotEmpty ? list[0]["amount"] : Null; 
   }
   Future<Expense> insert(Expense expense) async {
      final db = await database; 
      var maxIdResult = await db.rawQuery(
         "SELECT MAX(id)+1 as last_inserted_id FROM Expense"
      );
      var id = maxIdResult.first["last_inserted_id"]; 
      var result = await db.rawInsert(
         "INSERT Into Expense (id, amount, date, category)" 
         " VALUES (?, ?, ?, ?)", [
            id, expense.amount, expense.date.toString(), expense.category
         ]
      );
      return Expense(id, expense.amount, expense.date, expense.category); 
   }
   update(Expense product) async {
      final db = await database; 
      var result = await db.update(
         "Expense", product.toMap(), where: "id = ?", whereArgs: [product.id]
      ); 
      return result; 
   }
   delete(int id) async {
      final db = await database;
      db.delete("Expense", where: "id = ?", whereArgs: [id]);
   }
}

这里，

database 是获取 SQLiteDbProvider 对象的属性。
initDB 是一个用于选择和打开 SQLite 数据库的方法。

创建一个新文件 ExpenseListModel.dart 以创建 ExpenseListModel。该模型的目的是在内存中保存用户支出的完整信息，并在用户内存中的支出发生变化时更新应用程序的用户界面。它基于 scoped_model 包中的 Model 类。它具有以下属性和方法：

_items - 支出的私有列表。
items - 作为 UnmodifiableListView<Expense> 的 _items 的 getter，以防止对列表进行意外或意外更改。
totalExpense - 基于 items 变量的总支出的 getter。

double get totalExpense {
   double amount = 0.0; 
   for(var i = 0; i < _items.length; i++) { 
      amount = amount + _items[i].amount; 
   } 
   return amount; 
}

load - 用于从数据库加载完整支出并将其加载到 _items 变量中。它还会调用 notifyListeners 以更新 UI。

void load() {
   Future<List<Expense>> 
   list = SQLiteDbProvider.db.getAllExpenses(); 
   list.then( (dbItems) {
      for(var i = 0; i < dbItems.length; i++) { 
         _items.add(dbItems[i]); 
      } notifyListeners(); 
   });
}

byId - 用于从 _items 变量获取特定支出。

Expense byId(int id) { 
   for(var i = 0; i < _items.length; i++) { 
      if(_items[i].id == id) { 
         return _items[i]; 
      } 
   }
   return null; 
}

add - 用于将新的支出项添加到 _items 变量以及数据库中。它还会调用 notifyListeners 以更新 UI。

void add(Expense item) {
   SQLiteDbProvider.db.insert(item).then((val) { 
      _items.add(val); notifyListeners(); 
   }); 
}

Update - 用于将支出项更新到 _items 变量以及数据库中。它还会调用 notifyListeners 以更新 UI。

void update(Expense item) {
   bool found = false;
   for(var i = 0; i < _items.length; i++) {
      if(_items[i].id == item.id) {
         _items[i] = item; 
         found = true; 
         SQLiteDbProvider.db.update(item); break; 
      } 
   }
   if(found) notifyListeners(); 
}

delete - 用于从 _items 变量以及数据库中删除现有的支出项。它还会调用 notifyListeners 以更新 UI。

void delete(Expense item) { 
   bool found = false; 
   for(var i = 0; i < _items.length; i++) {
      if(_items[i].id == item.id) {
         found = true; 
         SQLiteDbProvider.db.delete(item.id); 
         _items.removeAt(i); break; 
      }
   }
   if(found) notifyListeners(); 
}

ExpenseListModel 类的完整代码如下：

import 'dart:collection'; 
import 'package:scoped_model/scoped_model.dart'; 
import 'Expense.dart'; 
import 'Database.dart'; 

class ExpenseListModel extends Model { 
   ExpenseListModel() { 
      this.load(); 
   } 
   final List<Expense> _items = []; 
   UnmodifiableListView<Expense> get items => 
   UnmodifiableListView(_items); 
   
   /*Future<double> get totalExpense { 
      return SQLiteDbProvider.db.getTotalExpense(); 
   }*/ 
   
   double get totalExpense {
      double amount = 0.0;
      for(var i = 0; i < _items.length; i++) { 
         amount = amount + _items[i].amount; 
      } 
      return amount; 
   }
   void load() {
      Future<List<Expense>> list = SQLiteDbProvider.db.getAllExpenses(); 
      list.then( (dbItems) {
         for(var i = 0; i < dbItems.length; i++) {
            _items.add(dbItems[i]); 
         } 
         notifyListeners(); 
      }); 
   }
   Expense byId(int id) {
      for(var i = 0; i < _items.length; i++) { 
         if(_items[i].id == id) { 
            return _items[i]; 
         } 
      }
      return null; 
   }
   void add(Expense item) {
      SQLiteDbProvider.db.insert(item).then((val) {
         _items.add(val);
         notifyListeners();
      }); 
   }
   void update(Expense item) {
      bool found = false; 
      for(var i = 0; i < _items.length; i++) {
         if(_items[i].id == item.id) {
            _items[i] = item; 
            found = true; 
            SQLiteDbProvider.db.update(item); 
            break; 
         }
      }
      if(found) notifyListeners(); 
   }
   void delete(Expense item) {
      bool found = false; 
      for(var i = 0; i < _items.length; i++) {
         if(_items[i].id == item.id) {
            found = true; 
            SQLiteDbProvider.db.delete(item.id); 
            _items.removeAt(i); break; 
         }
      }
      if(found) notifyListeners(); 
   }
}

打开 main.dart 文件。导入如下所示的类：

import 'package:flutter/material.dart'; 
import 'package:scoped_model/scoped_model.dart'; 
import 'ExpenseListModel.dart'; 
import 'Expense.dart';

添加 main 函数并通过传递 ScopedModel<ExpenseListModel> widget 来调用 runApp。

void main() { 
   final expenses = ExpenseListModel(); 
   runApp(
      ScopedModel<ExpenseListModel>(model: expenses, child: MyApp(),)
   );
}

这里，

expenses 对象从数据库加载所有用户的支出信息。此外，当应用程序第一次打开时，它将创建具有正确表的所需数据库。
ScopedModel 在应用程序的整个生命周期中提供支出信息，并确保在任何时候都维护应用程序的状态。它使我们能够使用 StatelessWidget 而不是 StatefulWidget。

使用 MaterialApp widget 创建一个简单的 MyApp。

class MyApp extends StatelessWidget {
   // This widget is the root of your application. 
   @override 
   Widget build(BuildContext context) {
      return MaterialApp(
         title: 'Expense',
         theme: ThemeData(
            primarySwatch: Colors.blue, 
         ), 
         home: MyHomePage(title: 'Expense calculator'), 
      );
   }
}

创建 MyHomePage widget 以显示所有用户的支出信息以及顶部的总支出。右下角的浮动按钮将用于添加新的支出。

class MyHomePage extends StatelessWidget { 
   MyHomePage({Key key, this.title}) : super(key: key); 
   final String title; 
   @override 
   Widget build(BuildContext context) {
      return Scaffold(
         appBar: AppBar( 
            title: Text(this.title), 
         ), 
         body: ScopedModelDescendant<ExpenseListModel>(
            builder: (context, child, expenses) {
               return ListView.separated(
                  itemCount: expenses.items == null ? 1 
                  : expenses.items.length + 1, 
                  itemBuilder: (context, index) { 
                     if (index == 0) { 
                        return ListTile(
                           title: Text("Total expenses: " 
                           + expenses.totalExpense.toString(), 
                           style: TextStyle(fontSize: 24,
                           fontWeight: FontWeight.bold),) 
                        );
                     } else {
                        index = index - 1; 
                        return Dismissible( 
                           key: Key(expenses.items[index].id.toString()), 
                              onDismissed: (direction) { 
                              expenses.delete(expenses.items[index]); 
                              Scaffold.of(context).showSnackBar(
                                 SnackBar(
                                    content: Text(
                                       "Item with id, " 
                                       + expenses.items[index].id.toString() + 
                                       " is dismissed"
                                    )
                                 )
                              ); 
                           },
                           child: ListTile( onTap: () { 
                              Navigator.push(
                                 context, MaterialPageRoute(
                                    builder: (context) => FormPage(
                                       id: expenses.items[index].id,
                                       expenses: expenses, 
                                    )
                                 )
                              );
                           }, 
                           leading: Icon(Icons.monetization_on), 
                           trailing: Icon(Icons.keyboard_arrow_right), 
                           title: Text(expenses.items[index].category + ": " + 
                           expenses.items[index].amount.toString() + 
                           " \nspent on " + expenses.items[index].formattedDate, 
                           style: TextStyle(fontSize: 18, fontStyle: FontStyle.italic),))
                        ); 
                     }
                  },
                  separatorBuilder: (context, index) { 
                     return Divider(); 
                  }, 
               );
            },
         ),
         floatingActionButton: ScopedModelDescendant<ExpenseListModel>(
            builder: (context, child, expenses) {
               return FloatingActionButton( onPressed: () {
                  Navigator.push( 
                     context, MaterialPageRoute(
                        builder: (context) => ScopedModelDescendant<ExpenseListModel>(
                           builder: (context, child, expenses) { 
                              return FormPage( id: 0, expenses: expenses, ); 
                           }
                        )
                     )
                  ); 
                  // expenses.add(new Expense( 
                     // 2, 1000, DateTime.parse('2019-04-01 11:00:00'), 'Food')
                  ); 
                  // print(expenses.items.length); 
               },
               tooltip: 'Increment', child: Icon(Icons.add), ); 
            }
         )
      );
   }
}

这里，

ScopedModelDescendant 用于将支出模型传递到 ListView 和 FloatingActionButton widget 中。
ListView.separated 和 ListTile widget 用于列出支出信息。
Dismissible widget 用于使用滑动手势删除支出条目。
Navigator 用于打开支出条目的编辑界面。可以通过点击支出条目来激活它。

创建一个 FormPage widget。FormPage widget 的目的是添加或更新支出条目。它也处理支出条目的验证。

class FormPage extends StatefulWidget { 
   FormPage({Key key, this.id, this.expenses}) : super(key: key); 
   final int id; 
   final ExpenseListModel expenses; 
   
   @override _FormPageState createState() => _FormPageState(id: id, expenses: expenses); 
}
class _FormPageState extends State<FormPage> {
   _FormPageState({Key key, this.id, this.expenses}); 
   
   final int id; 
   final ExpenseListModel expenses; 
   final scaffoldKey = GlobalKey<ScaffoldState>(); 
   final formKey = GlobalKey<FormState>(); 
   
   double _amount; 
   DateTime _date; 
   String _category; 
   
   void _submit() {
      final form = formKey.currentState; 
      if (form.validate()) {
         form.save(); 
         if (this.id == 0) expenses.add(Expense(0, _amount, _date, _category)); 
            else expenses.update(Expense(this.id, _amount, _date, _category)); 
         Navigator.pop(context); 
      }
   }
   @override 
   Widget build(BuildContext context) {
      return Scaffold(
         key: scaffoldKey, appBar: AppBar(
            title: Text('Enter expense details'),
         ), 
         body: Padding(
            padding: const EdgeInsets.all(16.0), 
            child: Form(
               key: formKey, child: Column(
                  children: [
                     TextFormField( 
                        style: TextStyle(fontSize: 22), 
                        decoration: const InputDecoration( 
                           icon: const Icon(Icons.monetization_on), 
                           labelText: 'Amount', 
                           labelStyle: TextStyle(fontSize: 18)
                        ), 
                        validator: (val) {
                           Pattern pattern = r'^[1-9]\d*(\.\d+)?$'; 
                           RegExp regex = new RegExp(pattern); 
                           if (!regex.hasMatch(val)) 
                           return 'Enter a valid number'; else return null; 
                        }, 
                        initialValue: id == 0 
                        ? '' : expenses.byId(id).amount.toString(), 
                        onSaved: (val) => _amount = double.parse(val), 
                     ), 
                     TextFormField( 
                        style: TextStyle(fontSize: 22), 
                        decoration: const InputDecoration( 
                           icon: const Icon(Icons.calendar_today),
                           hintText: 'Enter date', 
                           labelText: 'Date', 
                           labelStyle: TextStyle(fontSize: 18), 
                        ), 
                        validator: (val) {
                           Pattern pattern = r'^((?:19|20)\d\d)[- /.]
                              (0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])$'; 
                           RegExp regex = new RegExp(pattern); 
                           if (!regex.hasMatch(val)) 
                              return 'Enter a valid date'; 
                           else return null; 
                        },
                        onSaved: (val) => _date = DateTime.parse(val), 
                        initialValue: id == 0 
                        ? '' : expenses.byId(id).formattedDate, 
                        keyboardType: TextInputType.datetime, 
                     ),
                     TextFormField(
                        style: TextStyle(fontSize: 22), 
                        decoration: const InputDecoration(
                           icon: const Icon(Icons.category),
                           labelText: 'Category', 
                           labelStyle: TextStyle(fontSize: 18)
                        ),
                        onSaved: (val) => _category = val, 
                        initialValue: id == 0 ? '' 
                        : expenses.byId(id).category.toString(),
                     ), 
                     RaisedButton( 
                        onPressed: _submit, 
                        child: new Text('Submit'), 
                     ), 
                  ],
               ),
            ),
         ),
      );
   }
}

这里，

TextFormField 用于创建表单条目。
TextFormField 的 validator 属性用于使用 RegEx 模式验证表单元素。
_submit 函数与 expenses 对象一起使用，将支出添加到数据库或更新数据库中的支出。

main.dart 文件的完整代码如下：

import 'package:flutter/material.dart'; 
import 'package:scoped_model/scoped_model.dart'; 
import 'ExpenseListModel.dart'; 
import 'Expense.dart'; 

void main() { 
   final expenses = ExpenseListModel(); 
   runApp(
      ScopedModel<ExpenseListModel>(
         model: expenses, child: MyApp(), 
      )
   ); 
}
class MyApp extends StatelessWidget {
   // This widget is the root of your application. 
   @override
   Widget build(BuildContext context) {
      return MaterialApp(
         title: 'Expense',
         theme: ThemeData(
            primarySwatch: Colors.blue, 
         ), 
         home: MyHomePage(title: 'Expense calculator'), 
      );
   }
}
class MyHomePage extends StatelessWidget {
   MyHomePage({Key key, this.title}) : super(key: key);
   final String title;

   @override 
   Widget build(BuildContext context) {
      return Scaffold(
         appBar: AppBar(
            title: Text(this.title),
         ),
         body: ScopedModelDescendant<ExpenseListModel>(
            builder: (context, child, expenses) { 
               return ListView.separated(
                  itemCount: expenses.items == null ? 1 
                  : expenses.items.length + 1, itemBuilder: (context, index) { 
                     if (index == 0) { 
                        return ListTile( title: Text("Total expenses: " 
                        + expenses.totalExpense.toString(), 
                        style: TextStyle(fontSize: 24,fontWeight: 
                        FontWeight.bold),) ); 
                     } else {
                        index = index - 1; return Dismissible(
                           key: Key(expenses.items[index].id.toString()), 
                           onDismissed: (direction) {
                              expenses.delete(expenses.items[index]); 
                              Scaffold.of(context).showSnackBar(
                                 SnackBar(
                                    content: Text(
                                       "Item with id, " + 
                                       expenses.items[index].id.toString() 
                                       + " is dismissed"
                                    )
                                 )
                              );
                           }, 
                           child: ListTile( onTap: () {
                              Navigator.push( context, MaterialPageRoute(
                                 builder: (context) => FormPage(
                                    id: expenses.items[index].id, expenses: expenses, 
                                 )
                              ));
                           }, 
                           leading: Icon(Icons.monetization_on), 
                           trailing: Icon(Icons.keyboard_arrow_right), 
                           title: Text(expenses.items[index].category + ": " + 
                           expenses.items[index].amount.toString() + " \nspent on " + 
                           expenses.items[index].formattedDate, 
                           style: TextStyle(fontSize: 18, fontStyle: FontStyle.italic),))
                        );
                     }
                  }, 
                  separatorBuilder: (context, index) {
                     return Divider(); 
                  },
               ); 
            },
         ),
         floatingActionButton: ScopedModelDescendant<ExpenseListModel>(
            builder: (context, child, expenses) {
               return FloatingActionButton(
                  onPressed: () {
                     Navigator.push(
                        context, MaterialPageRoute(
                           builder: (context)
                           => ScopedModelDescendant<ExpenseListModel>(
                              builder: (context, child, expenses) { 
                                 return FormPage( id: 0, expenses: expenses, ); 
                              }
                           )
                        )
                     );
                     // expenses.add(
                        new Expense(
                           // 2, 1000, DateTime.parse('2019-04-01 11:00:00'), 'Food'
                        )
                     );
                     // print(expenses.items.length); 
                  },
                  tooltip: 'Increment', child: Icon(Icons.add), 
               );
            }
         )
      );
   } 
}
class FormPage extends StatefulWidget {
   FormPage({Key key, this.id, this.expenses}) : super(key: key); 
   final int id; 
   final ExpenseListModel expenses; 
   
   @override 
   _FormPageState createState() => _FormPageState(id: id, expenses: expenses); 
}
class _FormPageState extends State<FormPage> {
   _FormPageState({Key key, this.id, this.expenses}); 
   final int id; 
   final ExpenseListModel expenses; 
   final scaffoldKey = GlobalKey<ScaffoldState>(); 
   final formKey = GlobalKey<FormState>(); 
   double _amount; DateTime _date; 
   String _category;
   void _submit() {
      final form = formKey.currentState; 
      if (form.validate()) {
         form.save(); 
         if (this.id == 0) expenses.add(Expense(0, _amount, _date, _category)); 
         else expenses.update(Expense(this.id, _amount, _date, _category)); 
         Navigator.pop(context); 
      } 
   } 
   @override 
   Widget build(BuildContext context) {
      return Scaffold(
         key: scaffoldKey, appBar: AppBar( 
            title: Text('Enter expense details'), 
         ), 
         body: Padding(
            padding: const EdgeInsets.all(16.0),
            child: Form(
               key: formKey, child: Column(
                  children: [
                     TextFormField(
                        style: TextStyle(fontSize: 22), 
                        decoration: const InputDecoration( 
                           icon: const Icon(Icons.monetization_on), 
                           labelText: 'Amount', 
                           labelStyle: TextStyle(fontSize: 18)
                        ), 
                        validator: (val) {
                           Pattern pattern = r'^[1-9]\d*(\.\d+)?$'; 
                           RegExp regex = new RegExp(pattern); 
                           if (!regex.hasMatch(val)) return 'Enter a valid number'; 
                           else return null; 
                        },
                        initialValue: id == 0 ? '' 
                        : expenses.byId(id).amount.toString(), 
                        onSaved: (val) => _amount = double.parse(val), 
                     ),
                     TextFormField(
                        style: TextStyle(fontSize: 22), 
                        decoration: const InputDecoration(
                           icon: const Icon(Icons.calendar_today), 
                           hintText: 'Enter date', 
                           labelText: 'Date', 
                           labelStyle: TextStyle(fontSize: 18), 
                        ),
                        validator: (val) {
                           Pattern pattern = r'^((?:19|20)\d\d)[- /.]
                           (0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])$'; 
                           RegExp regex = new RegExp(pattern); 
                           if (!regex.hasMatch(val)) return 'Enter a valid date'; 
                           else return null; 
                        },
                        onSaved: (val) => _date = DateTime.parse(val), 
                        initialValue: id == 0 ? '' : expenses.byId(id).formattedDate, 
                        keyboardType: TextInputType.datetime, 
                     ),
                     TextFormField(
                        style: TextStyle(fontSize: 22), 
                        decoration: const InputDecoration(
                           icon: const Icon(Icons.category), 
                           labelText: 'Category', 
                           labelStyle: TextStyle(fontSize: 18)
                        ), 
                        onSaved: (val) => _category = val, 
                        initialValue: id == 0 ? '' : expenses.byId(id).category.toString(), 
                     ),
                     RaisedButton(
                        onPressed: _submit, 
                        child: new Text('Submit'), 
                     ),
                  ],
               ),
            ),
         ),
      );
   }
}

现在，运行应用程序。
使用浮动按钮添加新的支出。
通过点击支出条目来编辑现有支出。
通过向任一方向滑动支出条目来删除现有支出。

应用程序的一些屏幕截图如下：

打印页面