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vb.netparametersoptional-parameters
Steve Duitsman
Steve Duitsman

Reputation: 2791

How to add an optional parameters/default value parameters in VB function?

How can I create a method that has optional parameters in it in Visual Basic?

Upvotes: 54

Views: 94486

Answers (2)

Marcelo Nuñez
Marcelo Nuñez

Reputation: 61

Bear in mind that the Optional parameter cannot be before a required argument.

Otherwise, the code below will produce an error:

Sub ErrMethod(Optional ByVal FlagArgument As Boolean = True, ByVal Param1 As String)
    If FlagArgument Then
        'Do something special
        Console.WriteLine(Param1)
    End If
End Sub

Even though it is a common error...it is not very well explained by the debugger.

It does make sense though if you think about it, imagine this call:

ErrMethod(???, Param1)

Upvotes: 4

Joel Coehoorn
Joel Coehoorn

Reputation: 415600

Use the Optional keyword and supply a default value. Optional parameters must be the last parameters defined, to avoid creating ambiguous function signatures.

Sub MyMethod(ByVal Param1 As String, Optional ByVal FlagArgument As Boolean = True)
    If FlagArgument Then
        'Do something special
        Console.WriteLine(Param1)
    End If

End Sub

Call it like this:

MyMethod("test1")

Or like this:

MyMethod("test2", False)

Upvotes: 105

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