If an attempted conversion fails, CType and DirectCast both throw an InvalidCastException error. This can adversely affect the performance of your application. TryCast returns Nothing (Visual Basic), so that instead of having to handle a possible exception, you need only test the returned result against Nothing.

You use the TryCast keyword the same way you use the CType Function and the DirectCast keyword. You supply an expression as the first argument and a type to convert it to as the second argument. TryCast operates only on reference types, such as classes and interfaces. It requires an inheritance or implementation relationship between the two types. This means that one type must inherit from or implement the other.

Errors and Failures

Conversion Keywords

The following example shows how to use TryCast.

Function PrintTypeCode(ByVal obj As Object) As String
    Dim objAsConvertible As IConvertible = TryCast(obj, IConvertible)
    If objAsConvertible Is Nothing Then
        Return obj.ToString() & " does not implement IConvertible"
    Else
        Return "Type code is " & objAsConvertible.GetTypeCode()
    End If
End Function

Concepts