如何在 ASP.Net Core 中验证上传的文件

您可以自定义验证属性MaxFileSizeAttribute，如下所示

MaxFileSizeAttribute个

public class MaxFileSizeAttribute : ValidationAttribute
{
    private readonly int _maxFileSize;
    public MaxFileSizeAttribute(int maxFileSize)
    {
        _maxFileSize = maxFileSize;
    }

    protected override ValidationResult IsValid(
    object value, ValidationContext validationContext)
    {
        var file = value as IFormFile;
        if (file != null)
        {
           if (file.Length > _maxFileSize)
            {
                return new ValidationResult(GetErrorMessage());
            }
        }

        return ValidationResult.Success;
    }

    public string GetErrorMessage()
    {
        return $"Maximum allowed file size is { _maxFileSize} bytes.";
    }
}

AllowedExtensionsAttribute个

public class AllowedExtensionsAttribute : ValidationAttribute
{
    private readonly string[] _extensions;
    public AllowedExtensionsAttribute(string[] extensions)
    {
        _extensions = extensions;
    }
    
    protected override ValidationResult IsValid(
    object value, ValidationContext validationContext)
    {
        var file = value as IFormFile;
        if (file != null)
        {
            var extension = Path.GetExtension(file.FileName);
            if (!_extensions.Contains(extension.ToLower()))
            {
                return new ValidationResult(GetErrorMessage());
            }
        }
        
        return ValidationResult.Success;
    }

    public string GetErrorMessage()
    {
        return $"This photo extension is not allowed!";
    }
}

将MaxFileSize属性和AllowedExtensions属性添加到Photo属性

public class UserViewModel
{
        [Required(ErrorMessage = "Please select a file.")]
        [DataType(DataType.Upload)]
        [MaxFileSize(5* 1024 * 1024)]
        [AllowedExtensions(new string[] { ".jpg", ".png" })]
        public IFormFile Photo { get; set; }
 }