编写一段Csharp语言 用于wpf中创建一个可折叠列表 列表包含文件名、用户名、时间 列表数据通过mvvm模式绑定 并且用按钮可以切换按用户名折叠还是按文件名折叠

很高兴为您解答问题！以下是您要求的 C# 代码：

首先，我们需要先创建一个 Model 层，定义列表信息：

public class ListItem
{
    public string FileName { get; set; }
    public string UserName { get; set; }
    public DateTime Time { get; set; }
}

接着，我们需要创建一个 ViewModel 层，用于处理业务逻辑和数据绑定：

public class ListViewModel : INotifyPropertyChanged
{
    private ObservableCollection<ListItem> _list;
    private bool _isUserNameFolded = true;

    public ObservableCollection<ListItem> List
    {
        get => _list;
        set
        {
            if (_list != value)
            {
                _list = value;
                OnPropertyChanged(nameof(List));
            }
        }
    }

    public bool IsUserNameFolded
    {
        get => _isUserNameFolded;
        set
        {
            if (_isUserNameFolded != value)
            {
                _isUserNameFolded = value;
                OnPropertyChanged(nameof(IsUserNameFolded));
                UpdateList();
            }
        }
    }

    public ListViewModel()
    {
        // 初始化列表数据
        List = new ObservableCollection<ListItem>
        {
            new ListItem { FileName = "file1", UserName = "user1", Time = DateTime.Now },
            new ListItem { FileName = "file2", UserName = "user2", Time = DateTime.Now.AddDays(-1) },
            new ListItem { FileName = "file3", UserName = "user3", Time = DateTime.Now.AddDays(-2) },
            new ListItem { FileName = "file4", UserName = "user4", Time = DateTime.Now.AddDays(-3) }
        };
        UpdateList();
    }

    private void UpdateList()
    {
        if (IsUserNameFolded)
        {
            // 按用户名折叠
            var group = List.GroupBy(x => x.UserName).Select(x => new
            {
                Key = x.Key,
                Items = x.ToList()
            });
            var result = new ObservableCollection<ListItem>();
            foreach (var g in group)
            {
                result.Add(new ListItem
                {
                    FileName = $"{g.Key} ({g.Items.Count})",
                    UserName = g.Key,
                    Time = g.Items.OrderByDescending(x => x.Time).First().Time
                });
            }
            List = result;
        }
        else
        {
            // 按文件名折叠
            var group = List.GroupBy(x => x.FileName).Select(x => new
            {
                Key = x.Key,
                Items = x.ToList()
            });
            var result = new ObservableCollection<ListItem>();
            foreach (var g in group)
            {
                result.Add(new ListItem
                {
                    FileName = g.Key,
                    UserName = $"{g.Items.Select(x => x.UserName).Distinct().Count()} users",
                    Time = g.Items.OrderByDescending(x => x.Time).First().Time
                });
            }
            List = result;
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

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

然后，我们需要创建一个 View 层，用于显示界面和与用户交互：

<Window x:Class="WpfApp1.MainWindow"
        DataContext="{Binding RelativeSource={RelativeSource Self}}"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
        <DataTemplate x:Key="ListItemTemplate">
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding UserName}" Margin="5"/>
                <TextBlock Text="{Binding FileName}" Margin="5"/>
                <TextBlock Text="{Binding Time}" Margin="5"/>
            </StackPanel>
        </DataTemplate>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <StackPanel Orientation="Horizontal" Margin="5">
            <Button Content="按用户名折叠" Margin="5" Command="{Binding FoldByUserNameCommand}"/>
            <Button Content="按文件名折叠" Margin="5" Command="{Binding FoldByFileNameCommand}"/>
        </StackPanel>
        <ListView Grid.Row="1" ItemsSource="{Binding List}" ItemTemplate="{StaticResource ListItemTemplate}"
                  Margin="5" BorderThickness="1" BorderBrush="Gray">
        </ListView>
    </Grid>
</Window>

最后，在代码中实现页面逻辑：

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = new ListViewModel();
    }
}

对于按用户名折叠和按文件名折叠的操作，我们通过绑定按钮的 Command 属性来实现，在 ViewModel 中定义了对应的命令处理逻辑：

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

    public RelayCommand(Action execute, Func<bool> canExecute = null)
    {
        _execute = execute;
        _canExecute = canExecute;
    }

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

#pragma warning disable 67
    public event EventHandler CanExecuteChanged;
#pragma warning restore 67

    public void Execute(object parameter)
    {
        _execute?.Invoke();
    }
}

public class ListViewModel : INotifyPropertyChanged
{
    // ...

    public ICommand FoldByUserNameCommand => new RelayCommand(() =>
    {
        IsUserNameFolded = true;
    }, () => !IsUserNameFolded);

    public ICommand FoldByFileNameCommand => new RelayCommand(() =>
    {
        IsUserNameFolded = false;
    }, () => IsUserNameFolded);

    // ...
}

希望这段代码能够对您有所帮助！