RadioButtonFor删除默认检查

Question

在我的视图模型中有这样的属性：

public bool IsObligatory { get; set; }

并应由用户在post方法中填写。问题是，第二个单选按钮的默认值被选中。怎么移除它？即使我将模型中的IsObligatory属性设置为可选的，第二个单选按钮在默认情况下也会保持选中状态。

我的模型类与此问题相关：

public class Subject
{
   public int ID { get; set; }
   public string Name { get; set; }
   public int Semester { get; set; }

   public virtual ICollection<SubjectCourse> Courses { get; set; }
}
public class Course
{
   public int ID { get; set; }
   public string Abbreviation { get; set; }
   public string Title { get; set; }

   public virtual ICollection<SubjectCourse> Subjects { get; set; }
}
public class SubjectCourse
{
   public int SubjectCourseID { get; set; }
   public int SubjectID { get; set; }
   public int CourseID { get; set; }
   public bool? IsObligatory { get; set; }

   public virtual Subject Subject { get; set; }
   public virtual Course Course { get; set; }
}

我的观点模型：

public class SubjectVM
{
    public int? ID { get; set; }
    ...
    public List<SelectedCourseVM> SelectedCourses { get; set; }
    ...
}
public class SelectedCourseVM
{
    public int ID { get; set; }
    public string Title { get; set; }
    public bool IsObligatory { get; set; }
    public bool Selected { get; set; }
}

我的部分观点是：

<div class="form-group adding collapsable-courses">
   @for (int i = 0; i < Model.SelectedCourses.Count; i++)
   {
      <div class="panel-group" id="@Html.Id(@Model.SelectedCourses[i].Title)">
         <div class="panel panel-default">
            <div class="panel-heading">
               <h4 class="panel-title">
                  <a data-toggle="collapse" data-parent="#@Html.Id(@Model.SelectedCourses[i].Title)" href="#@Model.SelectedCourses[i].ID">
                     @Html.HiddenFor(model => model.SelectedCourses[i].ID)
                                        @Html.CheckBoxFor(model => model.SelectedCourses[i].Selected, new { @class = "checkbox-inline" })
                     <label class="course-label">@Model.SelectedCourses[i].Title</label>
                  </a>
               </h4>
            </div>
            <div id="@Model.SelectedCourses[i].ID" class="panel-collapse collapse in courses-to-collapse" toggle="false">
               <div class="panel-body">
                   <div class="isobligatory-radios">
                       <label class="radio-inline">
                           @Html.RadioButtonFor(model => model.SelectedCourses[i].IsObligatory, true)
                           Obavezan predmet
                       </label>
                       <label class="radio-inline">
                           @Html.RadioButtonFor(model => model.SelectedCourses[i].IsObligatory, false)
                           Izborni predmet
                       </label>
                   </div>
                </div>
             </div>
          </div>
      </div>
    }
</div>

Answer 1

这是因为IsObligatory属性的类型为bool，因此只能为true或false (默认值为false)。如果将类型更改为bool? (可空)，则默认值将为null，并且将选择两个单选按钮。

public bool? IsObligatory { get; set; }