public class ThemeViewLocationExpander : IViewLocationExpander
{
    // 将上下文中的信息提取为键值对，用于缓存键生成
    public void PopulateValues(ViewLocationExpanderContext context)
    {
        var theme = context.ActionContext.HttpContext.Request.Query["theme"].ToString();
        if (string.IsNullOrEmpty(theme))
        {
            theme = context.ActionContext.RouteData.Values["theme"]?.ToString();
        }
        context.Values["theme"] = theme ?? "default";
    }

    // 自定义视图查找路径
    public IEnumerable<string> ExpandViewLocations(
        ViewLocationExpanderContext context,
        IEnumerable<string> viewLocations)
    {
        if (context.Values.TryGetValue("theme", out var theme) && !string.IsNullOrEmpty(theme))
        {
            // 在原有路径前插入主题专属路径
            var themeLocation = $"/Themes/{theme}/Views/{{1}}/{{0}}.cshtml";
            var layoutLocation = $"/Themes/{theme}/Views/Shared/{{0}}.cshtml";

            return new[] { themeLocation, layoutLocation }.Concat(viewLocations);
        }

        return viewLocations;
    }
}

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllersWithViews(options =>
{
    options.ViewLocationExpanders.Add(new ThemeViewLocationExpander());
});

builder.Services.Configure<RazorViewEngineOptions>(options =>
{
    options.ViewLocationExpanders.Add(new ThemeViewLocationExpander());
});