StringExtensions.cs

/// <summary>
/// truncate string at the last full word before char limit and appends ...
/// </summary>
/// <param name="input">The input.</param>
/// <param name="length">The string length.</param>
/// <returns>The truncated string.</returns>
public static string TruncateAtWord(this string input, int length)
{
    if (input == null || input.Length < length)
    {
        return input;
    }

    int nextSpace = input.LastIndexOf(" ", length, StringComparison.Ordinal);
    return string.Format("{0}...", input.Substring(0, (nextSpace > 0) ? nextSpace : length).Trim());
}