WPF 使用MVVM的增删改查例子

以下是一个简单的使用MVVM实现增删改查的WPF例子：

Model类：

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

ViewModel类：

public class PersonViewModel : INotifyPropertyChanged
{
    private ObservableCollection<Person> _people;

    public ObservableCollection<Person> People
    {
        get { return _people; }
        set
        {
            if (_people != value)
            {
                _people = value;
                OnPropertyChanged("People");
            }
        }
    }

    private Person _selectedPerson;

    public Person SelectedPerson
    {
        get { return _selectedPerson; }
        set
        {
            if (_selectedPerson != value)
            {
                _selectedPerson = value;
                OnPropertyChanged("SelectedPerson");
            }
        }
    }

    public ICommand AddCommand { get; set; }
    public ICommand UpdateCommand { get; set; }
    public ICommand DeleteCommand { get; set; }

    public PersonViewModel()
    {
        // 初始化数据
        People = new ObservableCollection<Person>
        {
            new Person { Id=1, Name="Tom", Age=20 },
            new Person { Id=2, Name="Jerry", Age=30 },
        };

        // 添加命令
        AddCommand = new RelayCommand(AddPerson);
        // 修改命令
        UpdateCommand = new RelayCommand(UpdatePerson, CanUpdatePerson);
        // 删除命令
        DeleteCommand = new RelayCommand(DeletePerson, CanDeletePerson);
    }

    private void AddPerson()
    {
        // 创建新实例
        var person = new Person();
        // 将新实例添加到列表中
        People.Add(person);
        // 设置选中项为新实例
        SelectedPerson = person;
    }

    private void UpdatePerson()
    {
        // 更新选中项
        SelectedPerson.Name = "New Name";
        SelectedPerson.Age = 25;
    }

    private bool CanUpdatePerson()
    {
        // 如果没有选中项，则不能修改
        return SelectedPerson != null;
    }

    private void DeletePerson()
    {
        // 删除选中项
        People.Remove(SelectedPerson);
        // 清空选中项
        SelectedPerson = null;
    }

    private bool CanDeletePerson()
    {
        // 如果没有选中项，则不能删除
        return SelectedPerson != null;
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

View：

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525"
        DataContext="{StaticResource PersonViewModel}">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <StackPanel Grid.Row="0" Orientation="Horizontal">
            <Button Content="Add" Command="{Binding AddCommand}"/>
            <Button Content="Update" Command="{Binding UpdateCommand}"/>
            <Button Content="Delete" Command="{Binding DeleteCommand}"/>
        </StackPanel>
        <ListBox Grid.Row="1" ItemsSource="{Binding People}"
                 SelectedItem="{Binding SelectedPerson}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <TextBlock Text="{Binding Name}"/>
                        <TextBlock Text="{Binding Age}"/>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

在View中设置DataContext为ViewModel实例，并绑定AddCommand、UpdateCommand和DeleteCommand到Button的Command属性上，绑定People到ListBox的ItemsSource属性上，绑定SelectedPerson到ListBox的SelectedItem属性上。

使用RelayCommand类实现命令，该类可以在WPF中重复使用，代码如下：

public class RelayCommand : ICommand
{
    private readonly Action _execute;
    private readonly Func<bool> _canExecute;

    public RelayCommand(Action execute)
        : this(execute, null)
    {
    }

    public RelayCommand(Action execute, Func<bool> canExecute)
    {
        _execute = execute ?? throw new ArgumentNullException(nameof(execute));
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute();
    }

    public void Execute(object parameter)
    {
        _execute();
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }
}