首次使用MVC开发应用程序并遇到一个问题,在学生创建视图中填充一个教师列表的下拉列表。
我有2个模特
public class Student
{
[Required]
[Display(Name = "ID")]
public int ID { get; set; }
[Required]
[StringLength(100)]
[DataType(DataType.Text)]
[Display(Name = "First Name")]
public string FirstName { get; set; }
[Required]
[StringLength(100)]
[DataType(DataType.Text)]
[Display(Name = "Last Name")]
public string LastName { get; set; }
[Required]
[DataType(DataType.Date)]
[Display(Name = "Date of Birth")]
public DateTime? DateOfBirth { get; set; }
[Required]
[DataType(DataType.EmailAddress)]
[Display(Name = "Email Address")]
public string EmailAddress { get; set; }
[Required]
[DataType(DataType.PhoneNumber)]
[Display(Name = "Contact Number")]
public string ContactNumber { get; set; }
[Required]
[StringLength(100)]
[DataType(DataType.Text)]
[Display(Name = "Parent/Guardian Name")]
public string ParentGuardianName { get; set; }
public Teacher Teacher { get; set; }
public MembershipOption MembershipOption { get; set; }
public ICollection<Progress> Progress { get; set; }
public ICollection<Report> Report { get; set; }
[DataType(DataType.Date)]
[Display(Name = "Signed Up Date")]
public DateTime? SignedUpDate { get; set; }
[Display(Name = "Active")]
public bool Active { get; set; }
}
public class Teacher
{
[Required]
[Display(Name = "ID")]
public int ID { get; set; }
[Required]
[StringLength(100)]
[DataType(DataType.Text)]
[Display(Name = "First Name")]
public string FirstName { get; set; }
[StringLength(100)]
[DataType(DataType.Text)]
[Display(Name = "Last Name")]
public string LastName { get; set; }
[Display(Name = "Active")]
public bool Active { get; set; }
[Required]
[EmailAddress]
[Display(Name = "Email")]
public string Email { get; set; }
}
}
我有学生模型的创建视图,看起来像这样
<div class="form-group">
@Html.LabelFor(model => model.ParentGuardianName, htmlAttributes: new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.DropDownListFor(m => m.Teacher, // 1. Store selected value in Model.State;
// when page is rendered after postback,
// take selected value from Model.State.
// 2. Take list of values from Model.States
Model.Teacher,
// 3. Text for the first 'default' option
"- Please select a Teacher -",
//4. A class name to assign to <select> tag
new { @class = "form-control" })
@Html.ValidationMessageFor(model => model.Teacher, "", new { @class = "text-danger" })
</div>
</div>
由于教师为空,教师的下拉列表会抛出异常。
如何将教师下拉列表添加到此学生创建cshtml?
我假设我需要在调用学生模型时找到老师,但不确定它需要放在学生控制器的哪个位置?
答案 0 :(得分:1)
第二个参数应该是SelectListItem的列表,以便辅助方法可以使用该列表来生成SELECT选项。但是你试图传递Teacher
导航属性而不是那个!
您应该为视图创建一个视图模型,该模型具有接受表单输入值的属性。由于您要向视图添加下拉列表,因此请向视图模型添加2个属性。一个用于选定值,另一个用于我们需要用于呈现下拉列表的项目列表
public class CreateStudent
{
[Required]
[StringLength(100)]
[Display(Name = "First Name")]
public string FirstName { get; set; }
[Required]
[StringLength(100)]
[Display(Name = "Last Name")]
public string LastName { get; set; }
// to do : Add other properties AS NEEDED BY THE VIEW
// Do not just copy all the properties from Entity class
public List<SelectListItem> Teachers { set; get; }
[Required]
[DisplayName("Select Teacher")]
public int SelectedTeacherId { set; get; }
}
现在,在您的GET操作中,您需要创建此视图模型的对象,填充Teachers
集合属性并将对象发送到视图
public ActionResult Create()
{
var vm = new CreateStudent();
vm.Teachers = GetTeachers();
return View(vm);
}
private List<SelectListItem> GetTeachers()
{
return db.Teachers.Select(a => new SelectListItem
{
Value = a.Id.ToString(),
Text = a.Name
}).ToList();
}
现在在您的视图中,我们可以使用DropDownListFor帮助方法来渲染SELECT元素
@model CreateStudent
@using(Html.BeginForm())
{
@Html.LabelFor(a=>a.FirstName)
@Html.TextBoxFor(a=>a.FirstName)
@Html.LabelFor(a=>a.LastName)
@Html.TextBoxFor(a=>a.LastName)
@Html.LabelFor(a=>a.SelectedTeacherId)
@Html.DropDownListFor(a=>a.SelectedTeacherId , Model.Teachers, "select one")
<input type="submit" />
}
现在在您的HttpPost操作中,使用与您的操作方法参数相同的视图模型,并从其属性中读取值并使用它来创建实体类的新对象并保存它
[HttpPost]
public ActionResult Create(CreateStudent model)
{
if(ModelState.IsValid)
{
var s = new Student { FirstName=model.FirstName };
s.LastName = model.LastName;
// to do : Map other property values as well from view model
db.Students.Add(s);
db.SaveChanges();
return RedirectToAction("Index");
}
//Make sure to RELOAD the Teachers list for dropdown
model.Teachers = GetTeachers();
return View(model);
}