Export (0) Print
Expand All
0 out of 1 rated this helpful - Rate this topic

TypeOf Operator (Visual Basic)

Compares an object reference variable to a data type.

result = TypeOf objectexpression Is typename
result

Returned. A Boolean value.

objectexpression

Required. Any expression that evaluates to a reference type.

typename

Required. Any data type name.

The TypeOf operator determines whether the run-time type of objectexpression is compatible with typename. The compatibility depends on the type category of typename. The following table shows how compatibility is determined.

Type category of typename

Compatibility criterion

Class

objectexpression is of type typename or inherits from typename

Structure

objectexpression is of type typename

Interface

objectexpression implements typename or inherits from a class that implements typename

If the run-time type of objectexpression satisfies the compatibility criterion, result is True. Otherwise, result is False.

TypeOf is always used with the Is keyword to construct a TypeOf...Is expression.

The following example uses TypeOf...Is expressions to test the type compatibility of two object reference variables with various data types.


Dim refInteger As Object = 2
MsgBox("TypeOf Object[Integer] Is Integer? " & TypeOf refInteger Is Integer)
MsgBox("TypeOf Object[Integer] Is Double? " & TypeOf refInteger Is Double)
Dim refForm As Object = New System.Windows.Forms.Form
MsgBox("TypeOf Object[Form] Is Form? " & TypeOf refForm Is System.Windows.Forms.Form)
MsgBox("TypeOf Object[Form] Is Label? " & TypeOf refForm Is System.Windows.Forms.Label)
MsgBox("TypeOf Object[Form] Is Control? " & TypeOf refForm Is System.Windows.Forms.Control)
MsgBox("TypeOf Object[Form] Is IComponent? " & TypeOf refForm Is System.ComponentModel.IComponent)


The variable refInteger has a run-time type of Integer. It is compatible with Integer but not with Double. The variable refForm has a run-time type of Form. It is compatible with Form because that is its type, with Control because Form inherits from Control, and with IComponent because Form inherits from Component, which implements IComponent. However, refForm is not compatible with Label.

Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback

Community Additions

ADD
Show:
© 2014 Microsoft. All rights reserved.