Windows apps
Collapse the table of content
Expand the table of content
The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

String.IsNullOrEmpty Method (String)


Indicates whether the specified string is null or an Empty string.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

Public Shared Function IsNullOrEmpty (
	value As String
) As Boolean


Type: System.String

The string to test.

Return Value

Type: System.Boolean

true if the value parameter is null or an empty string (""); otherwise, false.

IsNullOrEmpty is a convenience method that enables you to simultaneously test whether a String is null or its value is Empty. It is equivalent to the following code:

result = s Is Nothing OrElse s = String.Empty

You can use the IsNullOrWhiteSpace method to test whether a string is null, its value is String.Empty, or it consists only of white-space characters.

A string is null if it has not been assigned a value (in C++ and Visual Basic) or if has explicitly been assigned a value of null. Although the composite formatting feature can gracefully handle a null string, as the following example shows, attempting to call one if its members throws a NullReferenceException.

Module Example
   Public Sub Main()
      Dim s As String

      Console.WriteLine("The value of the string is '{0}'", s)

         Console.WriteLine("String length is {0}", s.Length)
      Catch e As NullReferenceException
      End Try   
   End Sub
End Module
' The example displays the following output:
'     The value of the string is ''
'     Object reference not set to an instance of an object.

A string is empty if it is explicitly assigned an empty string ("") or String.Empty. An empty string has a Length of 0. The following example creates an empty string and displays its value and its length.

Dim s As String = ""
Console.WriteLine("The length of '{0}' is {1}.", s, s.Length)
' The example displays the following output:
'        The length of '' is 0.      

The following example examines three strings and determines whether each string has a value, is an empty string, or is null.

Class Sample
   Public Shared Sub Main()
      Dim s1 As String = "abcd"
      Dim s2 As String = ""
      Dim s3 As String = Nothing

      Console.WriteLine("String s1 {0}.", Test(s1))
      Console.WriteLine("String s2 {0}.", Test(s2))
      Console.WriteLine("String s3 {0}.", Test(s3))
   End Sub

   Public Shared Function Test(s As String) As String
      If String.IsNullOrEmpty(s) Then
         Return "is null or empty"
         Return String.Format("(""{0}"") is neither null nor empty", s)
      End If
   End Function 
End Class  
' The example displays the following output:
'       String s1 ("abcd") is neither null nor empty.
'       String s2 is null or empty.
'       String s3 is null or empty.

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Return to top
© 2017 Microsoft