c# - 自定义对象作为 MapRoutes 定义的控制器方法中的参数

Question

考虑这个 MapRoute：

MapRoute(
    "ResultFormat",
    "{controller}/{action}/{id}.{resultFormat}",
    new { controller = "Home", action = "Index", id = 0, resultFormat = "json" }
);

它是控制器方法：

public ActionResult Index(Int32 id, String resultFormat)
{
    var dc = new Models.DataContext();

    var messages = from m in dc.Messages where m.MessageId == id select m;

    if (resultFormat == "json")
    {
        return Json(messages, JsonRequestBehavior.AllowGet); // case 2
    }
    else
    {
        return View(messages); // case 1
    }
}

这是 URL 场景

• Home/Index/1将转到案例 1
• Home/Index/1.html将转到案例 1
• Home/Index/1.json将转到案例 2

这很好用。但我讨厌检查字符串。如何实现一个枚举作为resultFormat控制器方法中的参数？


一些伪代码来解释基本思想：

namespace Models
{
    public enum ResponseType
    {
        HTML = 0,
        JSON = 1,
        Text = 2
    }
}

地图路线：

MapRoute(
    "ResultFormat",
    "{controller}/{action}/{id}.{resultFormat}",
    new {
        controller = "Home",
        action = "Index",
        id = 0,
        resultFormat = Models.ResultFormat.HTML
    }
);

控制器方法签名：

public ActionResult Index(Int32 id, Models.ResultFormat resultFormat)

Answer 1

恕我直言，响应格式是一个横切关注点，而不是控制器来处理它。我建议您为此工作编写一个ActionFilter ：

[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, Inherited = true, AllowMultiple = true)]
public sealed class RespondToAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        var resultFormat = filterContext.RouteData.Values["resultFormat"] as string ?? "html";
        ViewResult viewResult = filterContext.Result as ViewResult;
        if (viewResult == null)
        {
            // The controller action did not return a view, probably it redirected
            return;
        }
        var model = viewResult.ViewData.Model;
        if (string.Equals("json", resultFormat, StringComparison.OrdinalIgnoreCase))
        {
            filterContext.Result = new JsonResult { Data = model };
        }
        // TODO: you could add some other response types you would like to handle
    }
}

然后稍微简化了您的控制器操作：

[RespondTo]
public ActionResult Index(int id)
{
    var messages = new string[0];
    if (id > 0)
    {
        // TODO: Fetch messages from somewhere
        messages = new[] { "message1", "message2" };
    }
    return View(messages);
}

ActionFilter 是一个可重用的组件，您可以将其应用于其他操作。

Answer 2

您的伪代码将正常工作。默认 ModelBinder 会自动将 url 中的字符串转换为 Models.ResultFormat 枚举。但正如 Darin Dimitrov 所说，制作 ActionFilter 会更好。

Answer 3

这是我想出的 ActionFilter：

public sealed class AlternateOutputAttribute :
                    ActionFilterAttribute, IActionFilter
{
    void IActionFilter.OnActionExecuted(ActionExecutedContext aec)
    {
        ViewResult vr = aec.Result as ViewResult;

        if (vr == null) return;

        var aof = aec.RouteData.Values["alternateOutputFormat"] as String;

        if (aof == "json") aec.Result = new JsonResult
        {
            JsonRequestBehavior = JsonRequestBehavior.AllowGet,
            Data = vr.ViewData.Model,
            ContentType = "application/json",
            ContentEncoding = Encoding.UTF8
        };
    }
}