在 ASP.NET Core 应用中，实现过滤器与控制器之间的数据传递是常见需求。通过合理选择方法，可以在请求处理流程中高效地共享信息。以下是几种典型且实用的实现方式：

1. 利用 HttpContext.Items 实现临时数据存储

HttpContext.Items 提供了一个轻量级的字典结构，用于在单个请求生命周期内保存临时数据，适用于跨组件共享上下文信息。

public class LoggingFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        context.HttpContext.Items["StartTime"] = DateTime.UtcNow;
    }

    public void OnActionExecuted(ActionExecutedContext context)
    {
        var startTime = context.HttpContext.Items["StartTime"] as DateTime?;
        if (startTime.HasValue)
        {
            var duration = DateTime.UtcNow - startTime.Value;
            // 记录执行耗时
        }
    }
}

public class ProductController : Controller
{
    public IActionResult Details(int id)
    {
        var startTime = HttpContext.Items["StartTime"] as DateTime?;
        return View(new { Id = id, StartTime = startTime });
    }
}

2. 通过 RouteData 传递路由相关参数

RouteData.Values 是路由系统的一部分，可用于在过滤器中动态注入或修改路由值，从而影响控制器逻辑。

public class AuthCheckFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        var role = context.RouteData.Values["role"] as string;
        if (string.IsNullOrEmpty(role))
        {
            context.RouteData.Values["role"] = "guest";
        }
    }

    public void OnActionExecuted(ActionExecutedContext context) { }
}

public class AdminController : Controller
{
    public IActionResult Dashboard()
    {
        var userRole = RouteData.Values["role"] as string;
        return View(new { UserRole = userRole });
    }
}

3. 修改 ActionArguments 实现参数注入

若需在执行前动态更改控制器方法的输入参数，可直接操作 ActionExecutingContext.ActionArguments 集合。

public class DefaultParamFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        if (context.ActionArguments.TryGetValue("searchTerm", out var value) && value == null)
        {
            context.ActionArguments["searchTerm"] = "default";
        }
    }

    public void OnActionExecuted(ActionExecutedContext context) { }
}

public IActionResult Search(string searchTerm)
{
    return View(new { Query = searchTerm });
}

4. 借助依赖注入实现共享状态管理

对于需要持久化或复杂状态共享的场景，推荐使用依赖注入注册一个共享服务，确保多个组件访问同一实例。

public interface IRequestContextService
{
    string CurrentUser { get; set; }
    Dictionary Metadata { get; }
}

public class RequestContextServiceImpl : IRequestContextService
{
    public string CurrentUser { get; set; } = "anonymous";
    public Dictionary Metadata { get; } = new();
}

// Startup.cs 配置
services.AddSingleton();

public class AuditFilter : IActionFilter
{
    private readonly IRequestContextService _context;

    public AuditFilter(IRequestContextService context)
    {
        _context = context;
    }

    public void OnActionExecuting(ActionExecutingContext context)
    {
        _context.CurrentUser = "admin";
        _context.Metadata["RequestTimestamp"] = DateTime.UtcNow;
    }

    public void OnActionExecuted(ActionExecutedContext context) { }
}

public class OrderController : Controller
{
    private readonly IRequestContextService _context;

    public OrderController(IRequestContextService context)
    {
        _context = context;
    }

    public IActionResult Create()
    {
        return View(new
        {
            User = _context.CurrentUser,
            Timestamp = _context.Metadata["RequestTimestamp"]
        });
    }
}

以上方法各有适用场景：Items 适合短期上下文；RouteData 用于路由关联；ActionArguments 支持参数重写；而依赖注入服务则更适合长期状态管理和复杂业务逻辑共享。