Why is this an issue?
A cast is an explicit
conversion, which is a way to tell the compiler the intent to convert from one type to another.
In Visual Basic, there are two explicit conversion operators:
Public Sub Method(Value As Object)
Dim i As Integer
i = DirectCast(Value, Integer) ' Direct casting from object holding an integer type to Integer
i = CType(Value, Integer) ' Conversion from the underlying type to Integer
End Sub
In most cases, the compiler will be able to catch invalid casts between incompatible value types or reference types.
However, the compiler will not be able to detect invalid casts to interfaces.
What is the potential impact?
Invalid casts will lead to unexpected behaviors or runtime errors such as InvalidCastException.
Exceptions
No issue is reported if the interface has no implementing class in the assembly.
How to fix it
To prevent an InvalidCastException from raising during an explicit conversion, it is recommended to use the TryCast operator. When the
conversion is not possible, the TryCast operator returns Nothing and will never raise an exception.
Code examples
Noncompliant code example
Public Interface IMyInterface
End Interface
Public Class Implementer
Implements IMyInterface
End Class
Public Class AnotherClass
End Class
Module Program
Sub Main()
Dim Another As New AnotherClass
Dim x As IMyInterface = DirectCast(Another, IMyInterface) ' Noncompliant: InvalidCastException is being thrown
End Sub
End Module
Compliant solution
Public Interface IMyInterface
End Interface
Public Class Implementer
Implements IMyInterface
End Class
Public Class AnotherClass
End Class
Module Program
Sub Main()
Dim Another As New AnotherClass
Dim x = TryCast(Another, IMyInterface) ' Compliant: but will always be Nothing
End Sub
End Module
Resources
Documentation
