如何格式化来自自定义验证器的错误消息

Question

我已经通过这种方式创建了一个自定义验证器：

public class IntArrayRequiredAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if ((!(value is int[] array) || !array.Any() || array.Any(item => item == 0)))
            return new ValidationResult(this.ErrorMessage);

        return ValidationResult.Success;
    }
}

并将其应用于模型属性：

    [IntArrayRequiredAttribute(ErrorMessage = "You must select {0}.")]
    [Display(Name = "Rol")]
    public int[] Roles { get; set; }

好，当验证失败时，显示此错误：

"You must select {0}."

如何返回错误消息，以便{0}自动被字段的显示名称替换，例如内置的验证器？

预期结果应为"You must select Rol."

编辑：

通过查看ValidationAttribute源代码，我读到：

    public ValidationResult GetValidationResult(object value, ValidationContext validationContext) {
        if (validationContext == null) {
            throw new ArgumentNullException("validationContext");
        }

        ValidationResult result = this.IsValid(value, validationContext);

        // If validation fails, we want to ensure we have a ValidationResult that guarantees it has an ErrorMessage
        if (result != null) {
            bool hasErrorMessage = (result != null) ? !string.IsNullOrEmpty(result.ErrorMessage) : false;
            if (!hasErrorMessage) {
                string errorMessage = this.FormatErrorMessage(validationContext.DisplayName);
                result = new ValidationResult(errorMessage, result.MemberNames);
            }
        }

        return result;
    }

我看到它调用了覆盖的IsValid方法，并格式化了消息。为什么我的格式不格式化？

如果我使用IsValid重载，则其格式正确，但是，我需要使用此方法，因为我需要validateContext来实现其他验证目的。

Answer 1

我认为参考源与实际代码不匹配，因为反射表明：

public ValidationResult GetValidationResult(object value, ValidationContext validationContext)
{
    if (validationContext == null)
    {
        throw new ArgumentNullException("validationContext");
    }
    ValidationResult validationResult = IsValid(value, validationContext);
    if (validationResult != null && (validationResult == null || string.IsNullOrEmpty(validationResult.ErrorMessage)))
    {
        string errorMessage = FormatErrorMessage(validationContext.DisplayName);
        validationResult = new ValidationResult(errorMessage, validationResult.MemberNames);
    }
    return validationResult;
}

因此，如果您想使所有内容都适合单个过载

protected override ValidationResult IsValid(object value, ValidationContext validationContext) {...}

您可以让基类执行ErrorMessage格式：

protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
    if ((!(value is int[] array) || !array.Any() || array.Any(item => item == 0)))
    {
       return new ValidationResult(null);
    }

    return ValidationResult.Success;
}

或者您可以自己格式化：

protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
    if ((!(value is int[] array) || !array.Any() || array.Any(item => item == 0)))
    {
        string errorMessage = FormatErrorMessage(validationContext.DisplayName);
        return new ValidationResult(errorMessage);
    }

    return ValidationResult.Success;
}