参数字典包含非空类型的参数“ id”的空条目 [英] The parameters dictionary contains a null entry for parameter 'id' of non-nullable type

问题描述

我正在尝试通过默认路径中的 id 参数从数据库中检索数据：

I'm trying to retrieve data from my db via the id parameter in my default route:

routes.MapRoute(
            "Default", // Route name
            "{controller}/{action}/{id}", // URL with parameters
            new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
        );

在此ActionResult中，我试图基于route id参数呈现自定义用户控件，因此我检索了请求页面的相关数据

In this ActionResult I'm trying to render a custom user control, based on the route id parameter so that I retrieve the relevant data for the page that's requested

public ActionResult InitPageNav(int id)
{
      PageModel page = PageNavHelper.GetPageByID(id);
      return PartialView("UserControls/_PageNavPartial", page);
}

编辑*

public static MvcHtmlString CreateMenuItems(this HtmlHelper helper, string action, string text)
{
     var menuItem = new TagBuilder("li");
     var link = new TagBuilder("a");

     //Get current action from route data
     var currentAction = (string)helper.ViewContext.RouteData.Values["action"];
     link.Attributes.Add("href", string.Format("/Home/{0}", action));

     if (currentAction == action)
     {
         menuItem.AddCssClass("selected");
         link.Attributes.Remove("href");
         link.Attributes.Add("href", string.Format("/Home/{0}", currentAction.ToString()));
     }

     link.SetInnerText(text);
     menuItem.InnerHtml = link.ToString();

     return MvcHtmlString.Create(menuItem.ToString());
 }

但我不断收到错误消息：

But I keep getting the error:

参数字典包含非空类型参数'id'的空条目

谁能发现我要去哪里错了？

Can anyone spot where I'm going wrong?

推荐答案

要调用该操作，URL中需要一个整数，例如：/ Home / InitPageNav / 1

To call the action, an integer is needed in the URL, like so: /Home/InitPageNav/1

或者您更改了操作方法以允许可为空的整数（但这没有意义，除非您具有默认页面，否则如果没有给出id则可以检索？ ）。

Either that or you change the action method to allow for a nullable integer (but that doesn't make sense, unless you have a default page you can retrieve if no id was given?).

如果您不想在网址中添加页面ID，则需要其他方法来标识该页面，例如标题？

If you don't want a page id in the url, you need something else to identify the page, like the title??

routes.MapRoute(
            "Default", // Route name
            "{controller}/{action}/{title}", // URL with parameters
            new { controller = "Home", action = "Index", title = UrlParameter.Optional } // Parameter defaults
        );

，然后执行以下操作：

public ActionResult InitPageNav(String title)
{
      PageModel page = PageNavHelper.GetPageByTitle(title);
      return PartialView("UserControls/_PageNavPartial", page);
}

只需确保处理title参数为空/空的情况。通常，您应该使用Mvc框架中已经存在的帮助程序/扩展程序来构建URL。

Just make sure to handle the case where the title parameter is empty/null. And generally you should use the helpers/extensions already present in the Mvc framework for building your urls.

@Html.ActionLink("Link text", "action", "controller", new { title = "whatever" }, null)

或在您更高级的帮助器中，

or in your more advanced helper,

public static MvcHtmlString CreateMenuItems(this UrlHelper url, string action, string text)
{
     var menuItem = new TagBuilder("li");
     var link = new TagBuilder("a");

     //Get current action from route data
     var currentAction = (string)helper.RequestContext.RouteData.Values["action"];
     link.Attributes.Add("href", url.Action(action, "home", new { title = "whatever" }));

     if (currentAction == action)
     {
         menuItem.AddCssClass("selected");
     }

     link.SetInnerText(text);
     menuItem.InnerHtml = link.ToString();

     return MvcHtmlString.Create(menuItem.ToString());
 }

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