Nullable(Of T).HasValue Property

May 11, 2014

Gets a value indicating whether the current Nullable(Of T) object has a value.

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

'Declaration
Public ReadOnly Property HasValue As Boolean

Property Value

Type: System.Boolean
true if the current Nullable(Of T) object has a value; false if the current Nullable(Of T) object has no value.

If the HasValue property is true, the value of the current Nullable(Of T) object can be accessed with the Value property.

The following code example returns the value of a Nullable(Of T) object if that object has a defined value; otherwise, a default value is returned.


' This code example demonstrates the Nullable(Of T).HasValue 
' and Value properties.


Class Example
   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim myNow As Nullable(Of DateTime)

      '  Assign the current date and time to myNow then display its value.
      myNow = DateTime.Now
      Display(outputBlock, myNow, "1) ")

      '  Assign null (Nothing in Visual Basic) to myNow then display its value.
      myNow = Nothing
      Display(outputBlock, myNow, "2) ")
   End Sub 'Main

   ' Display the date and time.
   Public Shared Sub Display(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal displayDateTime As Nullable(Of DateTime), _
                             ByVal title As String)

      ' If the HasValue property for the nullable of DateTime input argument is true, 
      ' display the value of the input argument; otherwise, display that no value is
      ' defined for the input value.
      outputBlock.Text &= title
      If displayDateTime.HasValue = True Then
         outputBlock.Text += String.Format("The date and time is {0:F}.", displayDateTime.Value) & vbCrLf
      Else
         outputBlock.Text &= "The date and time is not defined." & vbCrLf
      End If
   End Sub 'Display 

End Class 'Sample '

'This code example produces the following results:
'
'1) The date and time is Tuesday, April 19, 2005 4:16:06 PM.
'2) The date and time is not defined.
'


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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