不知道為什么，但由于某種原因，當我點擊提交按鈕時，視圖模型沒有系結DepartmentId，我收到一個錯誤：
值不能為空。
引數名稱：值說明：執行當前 Web 請求期間發生未處理的例外。請查看堆疊跟蹤以獲取有關錯誤及其源自代碼的位置的更多資訊。
不確定哪個值是空的，因為代碼沒有中斷，而是在點擊提交按鈕后顯示的訊息。
我假設它departmentId沒有正確系結到 CoursePreReqViewModel 中的 DepartmentID 屬性。
例外詳細資訊：System.ArgumentNullException：值不能為空。
引數名稱：值
看法：
@using (Html.BeginForm("Catalog", "Courses", FormMethod.Post, new { @class = "pure-form pure-form-aligned" }))
{
@Html.AntiForgeryToken()
<div class="row">
<div class="col">
<input id="myInput" class="form-control" type="text" placeholder="Search..">
</div>
<div class="col">
@Html.LabelFor(model => model.DepartmentId, htmlAttributes: new { @class = "control-label col-md-2" })
@Html.DropDownListFor(model => model.DepartmentId, Model.DepartmentList, "Department", new { @class = "form-control required", id = "department-list" })
@Html.ValidationMessageFor(model => model.DepartmentId)
</div>
<div class="col">
<button type="submit" class="btn btn-success">Submit</button>
</div>
</div>
}
控制器：
[HttpPost]
public ActionResult Catalog(CoursePreReqViewModel viewModel)
{
DepartmentRepo dRepo;
CoursesRepo cRepo;
MajorPreRequisitesRepo reqRepo;
using (context)
{
dRepo = new DepartmentRepo(context);
cRepo = new CoursesRepo(context);
viewModel.PopulateDepermentSelectList(dRepo.GetAllDepartments());
reqRepo = new MajorPreRequisitesRepo(context);
viewModel.Courses = cRepo.GetAllCoursesAndPreReqsByDepartment(viewModel.DepartmentId);
}
return View(viewModel);
}
查看型號：
public class CoursePreReqViewModel
{
[Required]
[Display(Name = "")]
public int DepartmentId { get; set; }
public IList<Course> Courses { get; set; }
public IList<MajorPreRequisite> CoursesAndPreReqs { get; set; }
[Display(Name = "Department: ")]
public IList<Department> Departments { get; set; }
public CoursePreReqViewModel() { }
public SelectList DepartmentList
{
get
{
return new SelectList(Departments, "Id", "Name");
}
}
public void PopulateDepartmentSelectList(IList<Department> populatedDepartments)
{
Departments = populatedDepartments;
}
}
uj5u.com熱心網友回復：
Sarthak 這里是另一個答案：這是 asp.net mvc fiddler https://dotnetfiddle.net/ARdtvr !!!顯示名稱需要是一個值！
uj5u.com熱心網友回復：
我可以幫助您保留您擁有的代碼，并回答您的問題。
控制器/類：
public class Course
{
public int CourseId { get; set; }
}
public class MajorPreRequisite
{
public int MajorPreRequisiteId { get; set; }
}
public class Department
{
public int Id { get; set; }
public string Name { get; set; }
}
public class CoursePreReqViewModel
{
//Make sure to comment this out -or- put this field in view
//try this first with your code, before you change code eg using a dictionary
//[Required]
//[Display(Name = "")]
public int DepartmentId { get; set; }
public IList<Course> Courses { get; set; }
public IList<MajorPreRequisite> CoursesAndPreReqs { get; set; }
[Display(Name = "Department: ")]
public IList<Department> Departments { get; set; }
public CoursePreReqViewModel() { }
public Dictionary<string, string> DepartmentList { get; set; }
public void GetAllCoursesAndPreReqsByDepartment(IList<Course> populateCourses)
{
Courses = populateCourses;
}
}
public class HomeController : Controller
{
[HttpPost]
public ActionResult Catalog(CoursePreReqViewModel viewModel)
{
//Put a breakpoint herre to see departmentid of user choice
return View();
}
public ActionResult Index11()
{
CoursePreReqViewModel viewModel = new CoursePreReqViewModel();
Dictionary<string, string> depts = new Dictionary<string, string>();
depts.Add("1", "deptOne");
depts.Add("2", "deptTwo");
viewModel.DepartmentList = depts;
IList<Course> courses = new List<Course>();
courses.Add(new Course { CourseId = 1 });
courses.Add(new Course { CourseId = 2 });
viewModel.GetAllCoursesAndPreReqsByDepartment(courses);
return View(viewModel);
}
看法：
@model WebApplication4what2.Controllers.CoursePreReqViewModel
@{
Layout = null;
}
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width" />
<title>Index11</title>
</head>
<body>
@using (Html.BeginForm("Catalog", "Home", FormMethod.Post, new { @class = "pure-form pure-form-aligned" }))
{
<div class="row">
<div class="col">
<input id="myInput" class="form-control" type="text" placeholder="Search..">
</div>
<div class="col">
@Html.LabelFor(model => model.DepartmentId, htmlAttributes: new { @class = "control-label col-md-2" })
@Html.DropDownListFor(model => model.DepartmentId, new SelectList(Model.DepartmentList, "Key", "Value"), Model.DepartmentId)
@Html.ValidationMessageFor(model => model.DepartmentId)
</div>
<div class="col">
<button type="submit" class="btn btn-success">Submit</button>
</div>
</div>
}
</body>
</html>
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