Util.IsNothing Method
The IsNothing method returns a Boolean value indicating whether
a variable has no data assigned to it. This method is very similar to the
function IsNothing in VB.NET; the difference is the method IsNothing
does check if the object is empty rather than just checking if the object
exists.
For instance IsNothing(i.Pictures)will return true if there are
pictures and false if there are no
pictures. On the other hand, VB's function IsNothing(i.Pictures) will
always return true because i.Pictures is an object.
The method IsNothing is very useful, yet not mandatory. The
other alternative is to compare the object against its "empty value". For
instance, an empty list (collection) of picture has a count of pictures equal to zero.
An empty string can be compared to "".
Using the method IsNothing is more reliable and faster than
comparing against the empty value. The following piece of code does determine if
an individual has a picture. Comparing if the picture name against an
empty string can produce incorrect results, as a picture without a name may
exists.
' Determine if there is a primary picture
If (Not Util.IsNothing(i.Pictures.Primary)) Then
' Your code there
End If
' Not recommended
If (i.Pictures.Primary.Name <> "") Then
' Your code there
End If
In summary, the method IsNothing returns true in the following
cases:
- The variable has never been initialized, and therefore empty.
- The variable is set to Nothing.
- The variable contains an empty string.
- The variable points to an object that is empty.
- The collection is empty. A collection is a list of items such as
individuals, families, pictures, occupations, etc.
Examples:
Dim strTest
Report.WriteBr Util.IsNothing(strTest) ' Returns true
strTest = "abc"
Report.WriteBr Util.IsNothing(strTest) ' Returns false
strTest = ""
Report.WriteBr Util.IsNothing(strTest) ' Returns true
Set strTest = Nothing
Report.WriteBr Util.IsNothing(strTest) ' Returns true
If (Not Util.IsNothing(i.Children)) Then
' The individual has children
End If
See Also:
Collection Object
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