Operador TypeOf (Visual Basic)

Artigo
08/08/2011

Compares an object reference variable to a data type.

result = TypeOf objectexpression Is typename

Parts

result
Returned. A Boolean value.
objectexpression
Required. Any expression that evaluates to a reference type.
typename
Required. Any data type name.

Comentários

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	objectexpressioné do tipotypename
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.

Exemplo

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.