如何在WPF MVVM模式下用C#通过Interaction Triggers实现窗口最大化最小化？

问题原因 #

你原来的方法无效，是因为WPF的Window类根本没有Maximize或Minimize这两个公共方法——它是通过WindowState属性来控制窗口状态的（可选值：WindowState.Normal/Maximized/Minimized），而CallMethodAction只能调用目标对象的公共方法，自然找不到对应方法导致失效。

下面给两种符合MVVM模式的解决方案：

方案1：自定义Interaction Action（View层处理，不侵入ViewModel） #

这种方式适合把窗口状态控制逻辑留在View层，ViewModel不需要感知窗口细节。

步骤1：创建自定义TriggerAction #

新建一个类，继承System.Windows.Interactivity.TriggerAction<DependencyObject>：

using System.Windows;
using System.Windows.Interactivity;

public class SetWindowStateAction : TriggerAction<DependencyObject>
{
    public static readonly DependencyProperty TargetWindowProperty =
        DependencyProperty.Register("TargetWindow", typeof(Window), typeof(SetWindowStateAction));

    public static readonly DependencyProperty TargetStateProperty =
        DependencyProperty.Register("TargetState", typeof(WindowState), typeof(SetWindowStateAction));

    public Window TargetWindow
    {
        get => (Window)GetValue(TargetWindowProperty);
        set => SetValue(TargetWindowProperty, value);
    }

    public WindowState TargetState
    {
        get => (WindowState)GetValue(TargetStateProperty);
        set => SetValue(TargetStateProperty, value);
    }

    protected override void Invoke(object parameter)
    {
        if (TargetWindow != null)
        {
            TargetWindow.WindowState = TargetState;
        }
    }
}

步骤2：在XAML中使用 #

替换原来的CallMethodAction，用这个自定义Action：

<!-- 先引入命名空间，假设你的自定义类在local命名空间下 -->
xmlns:local="clr-namespace:你的项目命名空间"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

<!-- 最大化按钮 -->
<Button Content="□" Height="20" Width="20">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="Click">
            <local:SetWindowStateAction 
                TargetWindow="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}"
                TargetState="Maximized"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
</Button>

<!-- 最小化按钮 -->
<Button Content="−" Height="20" Width="20">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="Click">
            <local:SetWindowStateAction 
                TargetWindow="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}"
                TargetState="Minimized"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
</Button>

<!-- 还原按钮（如果需要） -->
<Button Content="▭" Height="20" Width="20">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="Click">
            <local:SetWindowStateAction 
                TargetWindow="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}"
                TargetState="Normal"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
</Button>

方案2：MVVM完全解耦（ViewModel控制，通过服务/附加属性） #

如果希望ViewModel能控制窗口状态（比如根据业务逻辑自动最大化），可以用依赖注入或附加属性实现完全解耦。

方式A：窗口服务接口解耦 #

1. 定义服务接口：ViewModel只依赖接口，不直接引用Window

public interface IWindowService
{
    void MinimizeWindow();
    void MaximizeWindow();
    void RestoreWindow();
    void CloseWindow();
}

2. 实现服务（View层）：在窗口类中实现这个接口

public partial class MainWindow : Window, IWindowService
{
    public MainWindow()
    {
        InitializeComponent();
        // 把服务注入ViewModel，比如通过构造函数
        DataContext = new MainViewModel(this);
    }

    public void MinimizeWindow() => WindowState = WindowState.Minimized;
    public void MaximizeWindow() => WindowState = WindowState.Maximized;
    public void RestoreWindow() => WindowState = WindowState.Normal;
    public void CloseWindow() => Close();
}

3. ViewModel中使用服务：

public class MainViewModel
{
    private readonly IWindowService _windowService;

    public ICommand MinimizeCommand { get; }
    public ICommand MaximizeCommand { get; }

    public MainViewModel(IWindowService windowService)
    {
        _windowService = windowService;
        MinimizeCommand = new RelayCommand(_windowService.MinimizeWindow);
        MaximizeCommand = new RelayCommand(_windowService.MaximizeWindow);
    }
}

（注：RelayCommand是WPF中常见的命令实现类，如果没有自己的，可以写一个简单版本，或者用Prism等框架的命令）

4. XAML绑定命令：

<Button Content="−" Height="20" Width="20" Command="{Binding MinimizeCommand}"/>
<Button Content="□" Height="20" Width="20" Command="{Binding MaximizeCommand}"/>

方式B：附加属性绑定（更轻量） #

如果不想用服务，可以用附加属性把Window的WindowState绑定到ViewModel的属性：

1. 创建附加属性类：

public static class WindowStateBehavior
{
    public static readonly DependencyProperty BoundWindowStateProperty =
        DependencyProperty.RegisterAttached(
            "BoundWindowState",
            typeof(WindowState),
            typeof(WindowStateBehavior),
            new PropertyMetadata(WindowState.Normal, OnBoundWindowStateChanged));

    public static WindowState GetBoundWindowState(DependencyObject obj)
    {
        return (WindowState)obj.GetValue(BoundWindowStateProperty);
    }

    public static void SetBoundWindowState(DependencyObject obj, WindowState value)
    {
        obj.SetValue(BoundWindowStateProperty, value);
    }

    private static void OnBoundWindowStateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is Window window)
        {
            window.WindowState = (WindowState)e.NewValue;
        }
    }
}

2. ViewModel中添加属性：

private WindowState _currentWindowState;
public WindowState CurrentWindowState
{
    get => _currentWindowState;
    set => SetProperty(ref _currentWindowState, value); // 假设实现了INotifyPropertyChanged
}

// 命令示例
public ICommand MinimizeCommand => new RelayCommand(() => CurrentWindowState = WindowState.Minimized);
public ICommand MaximizeCommand => new RelayCommand(() => CurrentWindowState = WindowState.Maximized);

3. XAML绑定附加属性：

<Window ...
        local:WindowStateBehavior.BoundWindowState="{Binding CurrentWindowState, Mode=TwoWay}">

    <Button Content="−" Command="{Binding MinimizeCommand}"/>
    <Button Content="□" Command="{Binding MaximizeCommand}"/>
</Window>

内容的提问来源于stack exchange，提问作者Tamal Banerjee