可选参数必须是引用类型,可空类型,或者声明为可选参数.参数名称:参数`

Question

我正在.net MVC中创建一个演示应用程序.

下面是我的StudentController的代码片段.

public ActionResult Edit(int studentId)
{
    var std = studentList.Where(s => s.StudentId == studentId).FirstOrDefault();
    return View(std);
}

[HttpPost]
public ActionResult Edit(Student std)
{
    //write code to update student 

    return RedirectToAction("Index");
}

来自RouteConfig的代码片段:

routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

routes.MapRoute(
    name: "Default",
    url: "{controller}/{action}/{id}",
    defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);

当我点击url时,http://localhost:54977/student/Edit/1我会遇到异常.

The parameters dictionary contains a null entry for parameter 'studentId' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult Edit(Int32)' in 'MVC1.Controllers.StudentController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters.

但是当我点击url时它工作正常http://localhost:54976/student/Edit?StudentId=1.

我是.net MVC的新手.任何人都可以就此提出建议.

Answer 1

问题是由于您的路由配置.

 routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );

http:// localhost:54977/student/Edit/1中的第三个参数映射到{id}而不是studentId.

您有两种方法可以解决此问题:

1)更改参数名称

public ActionResult Edit(int id) {
        var std = studentList.Where(s => s.StudentId == id).FirstOrDefault();
        return View(std);
    }

2)为Edit添加新路由:

routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
       routes.MapRoute(
            "EditStudent",
            "Edit/{StudentId}",
            new { controller = "Student", action = "Edit" });
        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );