在ViewModel中获取窗口属性

基础概念

在MVVM架构中，ViewModel通常不应该直接访问视图层(如窗口)的属性，因为这违反了关注点分离的原则。ViewModel应该专注于业务逻辑和数据处理，而视图相关的操作应该由View来处理。

解决方案

1. 使用绑定系统

最推荐的方式是通过数据绑定将窗口属性暴露给ViewModel：

// 在窗口类中
public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = new MainViewModel();
        
        // 将窗口宽度绑定到ViewModel
        var binding = new Binding("WindowWidth") 
        { 
            Source = DataContext,
            Mode = BindingMode.TwoWay 
        };
        this.SetBinding(WidthProperty, binding);
    }
}

// ViewModel
public class MainViewModel : INotifyPropertyChanged
{
    private double _windowWidth;
    public double WindowWidth
    {
        get => _windowWidth;
        set
        {
            _windowWidth = value;
            OnPropertyChanged();
        }
    }
    
    public event PropertyChangedEventHandler PropertyChanged;
    
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

2. 使用附加行为(Attached Behavior)

public static class WindowProperties
{
    public static readonly DependencyProperty ViewModelProperty =
        DependencyProperty.RegisterAttached(
            "ViewModel",
            typeof(object),
            typeof(WindowProperties),
            new PropertyMetadata(null, OnViewModelChanged));

    public static void SetViewModel(Window element, object value)
    {
        element.SetValue(ViewModelProperty, value);
    }

    public static object GetViewModel(Window element)
    {
        return element.GetValue(ViewModelProperty);
    }

    private static void OnViewModelChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is Window window && e.NewValue is INotifyPropertyChanged vm)
        {
            vm.PropertyChanged += (sender, args) =>
            {
                if (args.PropertyName == "WindowWidth")
                {
                    window.Width = (double)vm.GetType().GetProperty("WindowWidth").GetValue(vm);
                }
            };
        }
    }
}

3. 使用事件聚合器(Event Aggregator)

// 定义事件
public class WindowSizeChangedEvent
{
    public double Width { get; set; }
    public double Height { get; set; }
}

// 在窗口代码中发布事件
private void Window_SizeChanged(object sender, SizeChangedEventArgs e)
{
    EventAggregator.Instance.Publish(new WindowSizeChangedEvent 
    { 
        Width = e.NewSize.Width, 
        Height = e.NewSize.Height 
    });
}

// 在ViewModel中订阅事件
public class MainViewModel
{
    public MainViewModel()
    {
        EventAggregator.Instance.Subscribe<WindowSizeChangedEvent>(e =>
        {
            WindowWidth = e.Width;
            WindowHeight = e.Height;
        });
    }
    
    public double WindowWidth { get; set; }
    public double WindowHeight { get; set; }
}