Question

如何解决此错误？

＆＃39; CreditsEarned＆＃39;关于学生的财产＆＃39;无法设置为＆＃39; null＆＃39; 值。您必须将此属性设置为类型的非null值＆＃39; System.Double＆＃39;

这是我的代码：

public class Student : Person
{
    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
    [Display(Name = "Enrollment Date")]
    public DateTime EnrollmentDate { get; set; }

    // Credits earned
    [Display(Name = "Credits Earned")]
    public double CreditsEarned { get; set; }

    // GPA
    [Display(Name = "GPA")]
    [Range(typeof(double), "0.7", "4.0")]
    public double Gpa { get; set; }


    public virtual ICollection<Enrollment> Enrollments { get; set; }
}

Answer 1

我可以问你为什么要将double类型设置为null？

默认情况下，C＃中的double类型不为null。您必须将其明确设置为null。

[Display(Name = "Credits Earned")]
public double? CreditsEarned { get; set; }

在声明类型后注意问号。在C＃中，这告诉编译器该类型可能被标记为可为空。

编辑：

请参阅以下链接：

1）Nullable Types in C#

2）Nullable Types in C# examples

Answer 2

已经提到使用Double?（类型为Double的ullable）来允许属性保存空值。

另一个选项可能是将属性初始化为0，并确保它始终为0或其他数字。

public class Student : Person
{
    // This will make sure the value is initially defined (to 0):
    public Student(){
        CreditsEarned = 0;
    }

    ...

    // Credits earned
    [Display(Name = "Credits Earned")]
    public double CreditsEarned { get; set; }

Answer 3

你应该试试

// Credits earned
[Display(Name = "Credits Earned")]
public double? CreditsEarned { get; set; }

将属性设置为类型为＆＃39; System.Double＆＃39;的非空值。

3 个答案: