validation - 下拉列表验证消息 mvc

Question

在我的 viewModel 我有

public string Addressline1 { get; set; }
public List<SelectListItem> StateList
    {
        get
        {
            return State.GetAllStates().Select(state => new SelectListItem { Selected = false, Text = state.Value, Value = state.Value }).ToList();
        }
    }

在我看来

@Html.DropDownListFor(model => model.StateCode, Model.StateList, "select")

当输入 AddressLine1 时，状态列表 DropDownList 选择是必需的。当下拉列表中除了默认的“选择”值之外没有选择任何状态时，如何验证并显示错误消息？

Answer 1

使用 [Required] 属性装饰您的 StateCode 属性:

[Required(ErrorMessage = "Please select a state")]
public string StateCode { get; set; }

public IEnumerable<SelectListItem> StateList
{
    get
    {
        return State
            .GetAllStates()
            .Select(state => new SelectListItem 
            { 
                Text = state.Value, 
                Value = state.Value 
            })
            .ToList();
    }
}

然后您可以添加相应的验证错误消息:

@Html.DropDownListFor(model => model.StateCode, Model.StateList, "select")
@Html.ValidationMessageFor(model => model.StateCode)

---

更新:

好吧，您似乎想根据 View 模型上的其他属性有条件地验证此 StateCode 属性。现在这是一个完全不同的故事，您应该在原始问题中对此进行解释。无论如何，一种可能性是编写自定义验证属性:

public class RequiredIfPropertyNotEmptyAttribute : ValidationAttribute
{
    public string OtherProperty { get; private set; }
    public RequiredIfPropertyNotEmptyAttribute(string otherProperty)
    {
        if (otherProperty == null)
        {
            throw new ArgumentNullException("otherProperty");
        }
        OtherProperty = otherProperty;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var property = validationContext.ObjectType.GetProperty(OtherProperty);
        if (property == null)
        {
            return new ValidationResult(string.Format(CultureInfo.CurrentCulture, "{0} is an unknown property", new object[]
            {
                OtherProperty
            }));
        }
        var otherPropertyValue = property.GetValue(validationContext.ObjectInstance, null) as string;
        if (string.IsNullOrEmpty(otherPropertyValue))
        {
            return null;
        }

        if (string.IsNullOrEmpty(value as string))
        {
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }

        return null;
    }
}

现在用这个属性装饰你的 StateCode 属性，像这样:

public string AddressLine1 { get; set; }

[RequiredIfPropertyNotEmpty("AddressLine1", ErrorMessage = "Please select a state")]
public string StateCode { get; set; }

现在假设你有以下表格:

@using (Html.BeginForm())
{
    <div>
        @Html.LabelFor(x => x.AddressLine1)
        @Html.EditorFor(x => x.AddressLine1)
    </div>

    <div>
        @Html.LabelFor(x => x.StateCode)
        @Html.DropDownListFor(x => x.StateCode, Model.States, "-- state --")
        @Html.ValidationMessageFor(x => x.StateCode)
    </div>

    <input type="submit" value="OK" />
}

仅当用户在 AddressLine1 字段中输入值时，才需要 StateCode 下拉菜单。