NOTE: This article has been updated and moved to: Confirm Before Deleting GridView Item.

When deleting an item in one of the ASP.NET grids, it would be nice to ask the user to confirm this is what they really meant to do. After all, it is very easy to mouse click somewhere by accident. And what would be even nicer is if this confirmation takes place on the client (browser) instead of requiring yet another round trip to the server.

Fortunately, this task is very easy to do. As you might expect, the answer is to use javascript. In some cases, setting up javascript on an ASP.NET page can get a little involved. However, a simple script can be added using the OnClientClick property, which is available with many ASP.NET controls.

Listing 1 shows part of the ASP.NET code for a GridView control. This code includes an ItemTemplate that defines a delete button and includes some confirmation javascript in the OnClientClick property.

<asp:GridView ID="GridView1" runat="server" />
  <Columns>
    <asp:TemplateField>
      <ItemTemplate>
        <asp:LinkButton ID="lnkDelete" runat="server"
          CausesValidation="false" 
          CommandName="DeleteItem"
          Text="Delete" CommandArgument='<%# Bind("ItemID") %>'
          OnClientClick="return confirm('Delete this item?');">
        </asp:LinkButton>
      </ItemTemplate>
    </asp:TemplateField>
  </Columns>
</asp:GridView>

Listing 1: Javascript to confirm deleting a GridView item.

This simple javascript calls confirm(), which returns true if the user selects Yes. The code associated with posting back the form and deleting the item only executes if this script returns true.

So, that’s a very simple technique that is easy to implement and works very well. And because it uses javascript, it doesn’t perform the postback to the server unless the user confirms they really do want to delete the grid item.

NOTE: This article has been updated and moved to: Validating Credit Card Numbers.

When using ASP.NET to process online credit card orders, it is a good idea if you can perform some sort of validation on the credit card number before submitting it to your processor. I recently had to write some code to process credit card orders and thought I’d share a bit of my code.

Fortunately, credit card numbers are created in a way that allows for some basic verification. This verification does not tell you if funds are available on the account and it certainly doesn’t tell whether or not the person submitting the order is committing credit card fraud. In fact, It’s possible that the card number is mistyped in such a way that it just happens to pass verification. But it does catch most typing errors and reduces bandwidth by catching those errors before trying to actually process the credit card.

To validate a credit card number, you start by adding the value of every other digit, starting from the right-most digit and working left. Next, you do the same thing with the digits skipped in the first step, but this time you double the value of each digit and add the value of each digit in the result. Finally, you add both totals together and if the result is evenly divisible by 10, then the card has passed validation.

Of course, this would be clearer with a bit of code and Listing 1 shows my IsCardNumberValid method.

public static bool IsCardNumberValid(string cardNumber)
{
  int i, checkSum = 0;
  // Compute checksum of every other digit starting from right-most digit
  for (i = cardNumber.Length - 1; i >= 0; i -= 2)
    checkSum += (cardNumber[i] - '0');
  // Now take digits not included in first checksum, multiple by two,
  // and compute checksum of resulting digits
  for (i = cardNumber.Length - 2; i >= 0; i -= 2)
  {
    int val = ((cardNumber[i] - '0') * 2);
    while (val > 0)
    {
      checkSum += (val % 10);
      val /= 10;
    }
  }
  // Number is valid if sum of both checksums MOD 10 equals 0
  return ((checkSum % 10) == 0);
}

Listing 1: Validating a credit card.

The IsCardNumberValid method assumes that all spaces and other non-digit characters have been stripped from the card number string. This is a straight forward task but Listing 2 shows the method I use for this.

public static string NormalizeCardNumber(string cardNumber)
{
  if (cardNumber == null)
    cardNumber = String.Empty;
  StringBuilder sb = new StringBuilder();
  foreach (char c in cardNumber)
  {
    if (Char.IsDigit(c))
      sb.Append(c);
  }
  return sb.ToString();
}

Listing 2: Removing all non-digit characters from a credit card number.

You will also be able to reduce bandwidth if you can avoid trying to submit a card that is not supported by the business. So another task that can be useful is determining the credit card type.

public enum CardType
{
  Unknown = 0,
  MasterCard = 1,
  VISA = 2,
  Amex = 3,
  Discover = 4,
  DinersClub = 5,
  JCB = 6,
  enRoute = 7
}
// Class to hold credit card type information
private class CardTypeInfo
{
  public CardTypeInfo(string regEx, int length, CardType type)
  {
    RegEx = regEx;
    Length = length;
    Type = type;
  }
  public string RegEx { get; set; }
  public int Length { get; set; }
  public CardType Type { get; set; }
}
// Array of CardTypeInfo objects. Used by GetCardType() to identify credit card types.
private static CardTypeInfo[] _cardTypeInfo =
{
  new CardTypeInfo("^(51|52|53|54|55)", 16, CardType.MasterCard),
  new CardTypeInfo("^(4)", 16, CardType.VISA),
  new CardTypeInfo("^(4)", 13, CardType.VISA),
  new CardTypeInfo("^(34|37)", 15, CardType.Amex),
  new CardTypeInfo("^(6011)", 16, CardType.Discover),
  new CardTypeInfo("^(300|301|302|303|304|305|36|38)", 14, CardType.DinersClub),
  new CardTypeInfo("^(3)", 16, CardType.JCB),
  new CardTypeInfo("^(2131|1800)", 15, CardType.JCB),
  new CardTypeInfo("^(2014|2149)", 15, CardType.enRoute),
};
public static CardType GetCardType(string cardNumber)
{
  foreach (CardTypeInfo info in _cardTypeInfo)
  {
    if (cardNumber.Length == info.Length && Regex.IsMatch(cardNumber, info.RegEx))
      return info.Type;
  }
  return CardType.Unknown;
}

Listing 3: Determining a credit card’s type.

Listing 3 is my code to determine a credit card’s type. I’m a big fan of table-driven code, when it makes sense, and so I created an array of CardTypeInfo objects. The GetCardType() method simply loops through this array, looking for the first description that would match the credit card number being tested. As before, this routine assumes all non-digit characters have been removed from the credit card number string.

The main reason I like table-driven code is because it makes the code simpler. This results in code that is easier to read and modify. GetCardType() returns a value from the CardType enum. CardType.Unknown is returned if the card number doesn’t match any card descriptions in the table.

Writing code to process credit cards involves a number of issues that need to be addressed. Hopefully, this code will give you a leg up on addressing a couple of them.