1  /// <summary>
 2         /// Is valid?
 3         /// </summary>
 4         /// <param name="context">Validation context</param>
 5         /// <returns>Result</returns>
 6         protected override bool IsValid(PropertyValidatorContext context)
 7         {
 8             var ccValue = context.PropertyValue as string;
 9             if (string.IsNullOrWhiteSpace(ccValue))
10                 return false;
11 
12             ccValue = ccValue.Replace(" ", "");
13             ccValue = ccValue.Replace("-", "");
14 
15             var checksum = 0;
16             var evenDigit = false;
17 
18             //http://www.beachnet.com/~hstiles/cardtype.html
19             foreach (var digit in ccValue.Reverse())
20             {
21                 if (!char.IsDigit(digit))
22                     return false;
23 
24                 var digitValue = (digit - ‘0‘) * (evenDigit ? 2 : 1);
25                 evenDigit = !evenDigit;
26 
27                 while (digitValue > 0)
28                 {
29                     checksum += digitValue % 10;
30                     digitValue /= 10;
31                 }
32             }
33 
34             return (checksum % 10) == 0;
35         }