string.IsNullOrEmpty(string) vs. string.IsNullOrWhiteSpace(string)

Question

Is use of string.IsNullOrEmpty(string) when checking a string considered as bad practice when there is string.IsNullOrWhiteSpace(string) in .NET 4.

Answer 1

Here is the actual implementation of both methods ( decompiled using dotPeek)

[TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    public static bool IsNullOrEmpty(string value)
    {
      if (value != null)
        return value.Length == 0;
      else
        return true;
    }

    /// <summary>
    /// Indicates whether a specified string is null, empty, or consists only of white-space characters.
    /// </summary>
    /// 
    /// <returns>
    /// true if the <paramref name="value"/> parameter is null or <see cref="F:System.String.Empty"/>, or if <paramref name="value"/> consists exclusively of white-space characters.
    /// </returns>
    /// <param name="value">The string to test.</param>
    public static bool IsNullOrWhiteSpace(string value)
    {
      if (value == null)
        return true;
      for (int index = 0; index < value.Length; ++index)
      {
        if (!char.IsWhiteSpace(value[index]))
          return false;
      }
      return true;
    }

Answer 2

It says it all IsNullOrEmpty() does not include white spacing while IsNullOrWhiteSpace() does!

IsNullOrEmpty() If string is:
-Null
-Empty

IsNullOrWhiteSpace() If string is:
-Null
-Empty
-Contains White Spaces Only

Answer 3

string.IsNullOrEmpty(str) - if you'd like to check string value has been provided

string.IsNullOrWhiteSpace(str) - basically this is already a sort of business logic implementation (i.e. why " " is bad, but something like "~~" is good).

My advice - do not mix business logic with technical checks. So, for example, string.IsNullOrEmpty is the best to use at the beginning of methods to check their input parameters.