c# - 即使在添加所需的命名空间后也会出现“必需”错误

Question

看看下面的代码，我正在使用 required(System.ComponentModel.DataAnnotations) 命名空间，但它一直向我显示红色波浪线，并显示无法找到“type or namespace name 'required'”的错误(你是否缺少一个使用指令......)

using System.ComponentModel.DataAnnotations;

namespace SportsStore.Domain.Entities {

public class ShippingDetails {
    [Required(ErrorMessage = "Please enter a name")]
    public string Name { get; set; }

    [Required(ErrorMessage = "Please enter the first address line")]
    public string Line1 { get; set; }
    public string Line2 { get; set; }
    public string Line3 { get; set; }

    [Required(ErrorMessage = "Please enter a city name")]
    public string City { get; set; }

    [Required(ErrorMessage = "Please enter a state name")]
    public string State { get; set; }

    public string Zip { get; set; }

    [Required(ErrorMessage = "Please enter a country name")]
    public string Country { get; set; }

    public bool GiftWrap { get; set; }
}
}

Answer 1

右键单击项目引用。选择添加引用。

在 .Net 选项卡中选择 System.ComponentModel.DataAnnotations