VB .NET Language in a Nutshell

Name

IIf Function

Class

Microsoft.VisualBasic.Interaction

Syntax

IIf(expression, truepart, falsepart)

expression

Use: Required

Data Type: Boolean

Expression to be evaluated

truepart

Use: Required

Data Type: Any value or expression

Expression or value to return if expression is True

falsepart

Use: Required

Data Type: Any value or expression

Expression or value to return if expression is False

Return Value

The value or result of the expression indicated by truepart or falsepart

Description

Returns one of two results, depending on whether expression evaluates to True or False

Rules at a Glance

• IIf will evaluate only one of truepart or falsepart, depending on the value of expression.

• The IIf function is the equivalent of:

  Iftestexpression Then
      Return truepart
  Else
      Return falsepart
  End If

• truepart and falsepart can be a variable, constant, literal, expression, or the return value of a function call.

Programming Tips and Gotchas

• The IIf function is ideal for very simple tests resulting in single expressions. If you really feel the need, IIf function calls can be nested; however, your code can very quickly become difficult to read. The following code fragment illustrates the use of a nested IIf function:

  Dim x As Integer
  x = CInt(Text1.Text)
  MsgBox(IIf(x < 10, "Less than ten", IIf(x < 20, _
             "Less than 20", "Greater than 20")))

• In previous versions of VB, developers tended to avoid the IIf function in favor of the If statement for all but the most simple uses because of its poor performance. In VB.NET, ...