asp.net mvc 上传附件验证

1.使用验证特性

[RequiredCollection]
public ICollection<IFormFile> Attachments { get; set; }

2.自定义验证特性

public class RequiredCollectionAttribute : ValidationAttribute
{
    protected const string DefaultErrorMessageFormatString = "You must provide at least one.";

    public RequiredCollectionAttribute() : base(DefaultErrorMessageFormatString) { }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var collection = (ICollection) value;

        return collection == null || collection.Count >
            ? ValidationResult.Success
            : new ValidationResult(ErrorMessageString);
    }
}

3.提交请求验证

[HttpPost]
public async Task<IActionResult> Method(MethodViewModel viewModel)
{
    if (!ModelState.IsValid)
        return View(viewModel);
    ...
}

原文链接：http://stackoverflow.com/questions/35989885/mvc-icollectioniformfile-validationstate-always-set-to-skipped