custom file validation for .net core 2.0 - asp.net-core

Question

I am trying to make a custom file validation for my project which is based on .net core 2.
I want to validate file size and also file extension in order to prevent users from uploading large files and for example .png files.
I have searched a lot but I could not find anything that works.
Here is my file validation class :
public class FileTypeAttribute : ValidationAttribute, IClientModelValidator
{
private const int MaxSize = 1048576;
private const string _DefaultErrorMessage = "Only the following file types are allowed: {0}";
private IEnumerable<string> _ValidTypes { get; set; }
public string ValidTypes { get; set; }
public string ErrorMessageExtension { get; set; }
public string ErrorMessageSize { get; set; }
public FileTypeAttribute(string errorExtension, string errorSize, string vt)
{
ErrorMessageExtension = errorExtension;
ErrorMessageSize = errorSize;
_ValidTypes = vt.Split(',');
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
IFormFile file = value as IFormFile;
if (file != null)
{
if (!_ValidTypes.Any(e => file.FileName.EndsWith(e)))
{
return new ValidationResult(ErrorMessageExtension);
}
if (file.Length > MaxSize)
{
return new ValidationResult(ErrorMessageSize);
}
}
return ValidationResult.Success;
}
public void AddValidation(ClientModelValidationContext context)
{
MergeAttribute(context.Attributes, "data-val", "true");
var errorMessage = FormatErrorMessage(context.ModelMetadata.GetDisplayName());
MergeAttribute(context.Attributes, "data-val-fileextensions", ErrorMessageExtension);
MergeAttribute(context.Attributes, "data-val-maxfilesize", ErrorMessageSize);
}
private bool MergeAttribute(
IDictionary<string, string> attributes, string key, string value)
{
if (attributes.ContainsKey(key))
{
return false;
}
attributes.Add(key, value);
return true;
}
}
and here is the javascript code in my view:
$.validator.addMethod("FileType",
function (value, element, param) {
for (var i = 0; i < element.files.length; i++) {
var extension = getFileExtension(element.files[0].name);
if ($.inArray(extension, param.validtypes) === -1) {
return false;
}
}
return true;
});
$.validator.unobtrusive.adapters.add('FileType', ['validtypes'], function (options) {
console.log("value:");
options.rules.cannotbered = {};
options.messages["FileType"] = options.message;
});
function getFileExtension(fileName) {
if (/[.]/.exec(fileName)) {
return /[^.]+$/.exec(fileName)[0].toLowerCase();
}
return null;
}
and here is the entity class code in my project:
public class MyEntityClass
{
public int MyEntityClassId { get; set; }
[FileType("invalid format", "invalid size", "jpg,png,gif")]
public IFormFile Photo { get; set; }
}
Can anyone help me to know where the problem is?
Thanks in advance.