wpf mvvm demo

### WPF 使用 MVVM 模式的演示示例 #### 创建视图模型 (ViewModel) 为了展示如何在 WPF 中应用 MVVM 模式，可以创建一个简单的应用程序来管理待办事项列表。此例子将包括三个主要部分：Model、View 和 ViewModel。 ##### 定义数据模型 (Model) 定义 `TodoItem` 类作为数据模型： ```csharp public class TodoItem : INotifyPropertyChanged { private string _title; public string Title { get { return _title; } set { if (_title != value) { _title = value; OnPropertyChanged(nameof(Title)); } } } public event PropertyChangedEventHandler PropertyChanged; protected void OnPropertyChanged(string propertyName) { PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)); } } ``` ##### 实现命令类 (Command Class) 实现用于处理 UI 命令的辅助类 `RelayCommand`: ```csharp public class RelayCommand : ICommand { private readonly Action<object> _execute; private readonly Predicate<object> _canExecute; public RelayCommand(Action<object> execute, Predicate<object> canExecute = null) { _execute = execute ?? throw new ArgumentNullException(nameof(execute)); _canExecute = canExecute; } public bool CanExecute(object parameter) => _canExecute == null || _canExecute(parameter); public void Execute(object parameter) => _execute(parameter); public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } } ``` ##### 构建视图模型 (ViewModel) 构建 `MainViewModel`, 这里包含了业务逻辑以及与 View 的交互方法： ```csharp public class MainViewModel : INotifyPropertyChanged { private ObservableCollection<TodoItem> _todoItems; private TodoItem _selectedItem; public ObservableCollection<TodoItem> TodoItems { get { return _todoItems; } set { if (_todoItems != value) { _todoItems = value; OnPropertyChanged(nameof(TodoItems)); } } } public TodoItem SelectedItem { get { return _selectedItem; } set { if (_selectedItem != value) { _selectedItem = value; OnPropertyChanged(nameof(SelectedItem)); } } } public ICommand AddNewItemCommand { get; } public ICommand RemoveSelectedCommand { get; } public MainViewModel() { TodoItems = new ObservableCollection<TodoItem>(); AddNewItemCommand = new RelayCommand(param => { var newItem = new TodoItem(); TodoItems.Add(newItem); SelectedItem = newItem; }); RemoveSelectedCommand = new RelayCommand( param => TodoItems.Remove(SelectedItem), param => SelectedItem != null ); } public event PropertyChangedEventHandler PropertyChanged; protected virtual void OnPropertyChanged(string propertyName) { PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)); } } ``` #### 设计用户界面 (XAML) 最后，在 XAML 文件中绑定这些属性到控件上： ```xml <Window x:Class="WpfApp.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"> <Grid> <!-- ListView 绑定到 TodoItems --> <ListView ItemsSource="{Binding TodoItems}" SelectedItem="{Binding SelectedItem}"> <ListView.View> <GridView> <GridViewColumn Header="Task" DisplayMemberBinding="{Binding Title}"/> </GridView> </ListView.View> </ListView> <!-- 添加按钮 --> <Button Content="Add New Task" HorizontalAlignment="Left" VerticalAlignment="Bottom" Width="100" Command="{Binding AddNewItemCommand}" /> <!-- 删除选中的任务按钮 --> <Button Content="Remove Selected" HorizontalAlignment="Right" VerticalAlignment="Bottom" Width="100" Command="{Binding RemoveSelectedCommand}" /> </Grid> </Window> ``` 通过这种方式，实现了基于 MVVM 模式的简单待办事项管理器[^1]。