如何拦截第三方内部类实例创建并修改其ThemeName属性？

方法1：全局窗口事件拦截设置属性 #

WPF的Application提供WindowCreated事件，可捕获所有窗口创建时机，无论目标窗口是否为internal类。在App.xaml.cs中注册该事件，校验窗口类型后用反射设置ThemeName属性：

protected override void OnStartup(StartupEventArgs e)
{
    base.OnStartup(e);
    Application.Current.WindowCreated += (sender, args) =>
    {
        var window = args.Window;
        // 替换为你通过Type.GetType获取的目标窗口完整类型（格式：命名空间.类名, 程序集名）
        var targetWindowType = Type.GetType("ThirdParty.InternalWindow, ThirdPartyAssembly");
        if (targetWindowType != null && window.GetType() == targetWindowType)
        {
            var themeProp = targetWindowType.GetProperty("ThemeName", BindingFlags.Public | BindingFlags.Instance);
            themeProp?.SetValue(window, "None");
        }
    };
}

这个方案无需依赖额外框架，只要能准确获取目标窗口的类型信息即可生效。

方法2：用Harmony Hook目标窗口方法 #

如果WindowCreated触发时机过晚（窗口已应用错误样式），可以用Harmony这个运行时AOP库拦截目标窗口的构造或显示方法，提前设置属性：

1. 安装NuGet包：Install-Package Lib.Harmony
2. 编写Hook代码：

using HarmonyLib;
using System.Reflection;

public static class ThirdPartyWindowHook
{
    public static void InitHook()
    {
        var harmony = new Harmony("your.unique.hook.id");
        var targetType = Type.GetType("ThirdParty.InternalWindow, ThirdPartyAssembly");
        if (targetType == null) return;

        // 拦截构造函数，创建后立即设属性
        var ctor = targetType.GetConstructor(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance, Type.EmptyTypes);
        if (ctor != null)
        {
            harmony.Patch(ctor, postfix: new HarmonyMethod(typeof(ThirdPartyWindowHook).GetMethod(nameof(PostConstruct), BindingFlags.Static | BindingFlags.Public)));
        }

        // 拦截Show/ShowDialog，确保显示前属性已设置
        var showMethod = typeof(Window).GetMethod("Show");
        var showDialogMethod = typeof(Window).GetMethod("ShowDialog");
        if (showMethod != null)
        {
            harmony.Patch(showMethod, prefix: new HarmonyMethod(typeof(ThirdPartyWindowHook).GetMethod(nameof(PreShow), BindingFlags.Static | BindingFlags.Public)));
        }
        if (showDialogMethod != null)
        {
            harmony.Patch(showDialogMethod, prefix: new HarmonyMethod(typeof(ThirdPartyWindowHook).GetMethod(nameof(PreShow), BindingFlags.Static | BindingFlags.Public)));
        }
    }

    public static void PostConstruct(object __instance)
    {
        var targetType = Type.GetType("ThirdParty.InternalWindow, ThirdPartyAssembly");
        if (__instance.GetType() == targetType)
        {
            var themeProp = targetType.GetProperty("ThemeName", BindingFlags.Public | BindingFlags.Instance);
            themeProp?.SetValue(__instance, "None");
        }
    }

    public static bool PreShow(object __instance)
    {
        var targetType = Type.GetType("ThirdParty.InternalWindow, ThirdPartyAssembly");
        if (__instance.GetType() == targetType)
        {
            var themeProp = targetType.GetProperty("ThemeName", BindingFlags.Public | BindingFlags.Instance);
            themeProp?.SetValue(__instance, "None");
        }
        return true; // 继续执行原方法
    }
}

在App启动时调用ThirdPartyWindowHook.InitHook();即可。Harmony支持修改internal类成员，完美解决Castle无法处理internal类的问题。

方法3：反射直接设置实例属性 #

如果能控制目标窗口的创建时机（比如你自己调用Activator.CreateInstance），直接在创建后设置属性即可：

var targetType = Type.GetType("ThirdParty.InternalWindow, ThirdPartyAssembly");
if (targetType != null)
{
    var window = Activator.CreateInstance(targetType, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance, null, null, null);
    var themeProp = targetType.GetProperty("ThemeName", BindingFlags.Public | BindingFlags.Instance);
    themeProp?.SetValue(window, "None");
    // 如需显示窗口
    typeof(Window).GetMethod("Show")?.Invoke(window, null);
}

这个方案仅适用于你能主动创建窗口的场景，第三方控件自动创建的窗口无法用此方法拦截。

注意事项 #

• 目标窗口类型必须是完整格式：命名空间.类名, 程序集名，可通过Snoop工具确认
• 反射时注意BindingFlags，internal类的构造/属性可能需要添加BindingFlags.NonPublic
• 若ThemeName是枚举类型，需传入对应枚举值而非字符串，比如Enum.Parse(themeProp.PropertyType, "None")

内容的提问来源于stack exchange，提问作者Ryan Thomas