Range Validation with Excel using C#

Question

In Excel in C# how does one create a combo where it can sort the items and when one of them is clicked, the item appears alone?

Solution

if you want to use a validation for that purpose the following method was written by me to add a Validation and a small Infobox that appears when the user clicks on the cell:

/// <summary>
/// Adds a small Infobox and a Validation with restriction (only these values will be selectable) to the specified cell.
/// </summary>
/// <param name="worksheet">The excel-sheet</param>
/// <param name="rowNr">1-based row index of the cell that will contain the validation</param>
/// <param name="columnNr">1-based column index of the cell that will contain the validation</param>
/// <param name="title">Title of the Infobox</param>
/// <param name="message">Message in the Infobox</param>
/// <param name="validationValues">List of available values for selection of the cell. No other value, than this list is allowed to be used.</param>
/// <exception cref="Exception">Thrown, if an error occurs, or the worksheet was null.</exception>
public static void AddDataValidation(Worksheet worksheet, int rowNr, int columnNr, string title, string message, List<string> validationValues)
{
    //If the message-string is too long (more than 255 characters, prune it)
    if (message.Length > 255)
        message = message.Substring(0, 254);

    try
    {
        //The validation requires a ';'-separated list of values, that goes as the restrictions-parameter.
        //Fold the list, so you can add it as restriction. (Result is "Value1;Value2;Value3")
        //If you use another separation-character (e.g in US) change the ; appropriately (e.g. to the ,)
        string values = string.Join(";", validationValues);
        //Select the specified cell
        Range cell = worksheet.Cells[rowNr, columnNr];
        //Delete any previous validation
        cell.Validation.Delete();
        //Add the validation, that only allowes selection of provided values.
        cell.Validation.Add(XlDVType.xlValidateList, XlDVAlertStyle.xlValidAlertStop, XlFormatConditionOperator.xlBetween, values, Type.Missing);
        cell.Validation.IgnoreBlank = true;
        //Optional put a message there
        cell.Validation.InputTitle = title;
        cell.Validation.InputMessage = message;

   }
   catch (Exception exception)
    {
         //This part should not be reached, but is used for stability-reasons
         throw new Exception(String.Format("Error when adding a Validation with restriction to the specified cell Row:{0}, Column:{1}, Message: {2}", rowNr, columnNr, message), exception);

    }
}

If you don't need the Infobox, just leave out the parts where the variables title or message appear.

Comments

[lowatt]

Just copied your codes and it turns out that the drop-down list contains only one item holding the string values joined by ";". And where can we change the "global Split-Character" as you mentioned in comment? I can't google any result with that term.

[Alexander Pacha]

Excel uses different characters to split lists depending on your localisation. See en.wikipedia.org/wiki/Comma-separated_values. For example in Germany, the ; is used, whereas , is used in US/UK. I've updated my post to be more clear.

[ΩmegaMan]

This is a comment and not an answer.