How to validate MIME type of multiple selected file in c#

How can i validate using IValidator object? I need to check file name is empty or not? and the content type and the list is empty or not

need to give validation for

 [Required(ErrorMessage = "files should be mime types")]
        public string FileContentType =>ContentTypes.TryConvertFromFileExtension(FileToUpload?.FileExtension, FileToUpload?.File.ContentType ?? string.Empty);

not for list now.Then i need to use 

 return new()
            {
                Name= Name,
                ContentType = FileContentType, //here each file will come from a foreach of a image list
               
            };

We can use the System.IO.File class to validate the MIME type of multiple selected files.

foreach (var file in files)
{
    var fileInfo = new FileInfo(file);
    if (!IsValidMIMEType(fileInfo.Extension))
    {
        // Do something if the MIME type is not valid
    }
}

private bool IsValidMIMEType(string fileExtension)
{
    // Define a list of valid MIME types
    var validMIMETypes = new List { "image/jpg", "image/jpeg", "image/png", "application/pdf" };

    // Get the MIME type of the file based on its file extension
    var mimeType = MimeMapping.GetMimeMapping(fileExtension);

    // Return true if the MIME type is in the list of valid MIME types, otherwise return false
    return validMIMETypes.Contains(mimeType);
}

You can create your Custom attribute.

public class AllowedExtensionsAttribute : ValidationAttribute
{
    private readonly string[] _extensions;
    public AllowedExtensionsAttribute(string[] extensions)
    {
        _extensions = extensions;
    }

    protected override ValidationResult IsValid(
    object value, ValidationContext validationContext)
    {
        var files = value as IList;
        foreach(var file in files)
        {
            var extension = Path.GetExtension(file.FileName);
            if (file != null)
            {
                if (!_extensions.Contains(extension.ToLower()))
                {
                    return new ValidationResult(GetErrorMessage(file.FileName));
                }
            }
        }
        
        return ValidationResult.Success;
    }

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

Then you can use it on property. 

[AllowedExtensions(new string[] { ".jpg",".png"})]
 public IList Photo { get; set; }

Source : https://stackoverflow.com/questions/62727427/how-to-validate-uploaded-files-in-asp-net-mvc

Thanks.