How to call method written in VB.NET from C# with optional arguments

Question

I have a method written in VB.NET. It looks like this:

Shared Sub SomeMethod(ByVal Id As Guid, 
                      Optional ByVal str1 As String = "foo", 
                      Optional ByVal str2 As String = "")

I want to call this method from C# 3.0 and I want it to use its default arguments. I tried passing System.Reflection.Missing.Value, but I cannot cast it as String.

Is there any way to do that?

Thanks in advance for help.

Henk Holterman · Accepted Answer · 2010-03-03 13:05:15Z

9

No, in C#3 you simply have to pass all parameters. C#4 will have optional and named parameters.

You could off course create a few overloaded variations, but that is only an approximation.

answered Mar 3, 2010 at 13:05

Henk Holterman

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2 Comments

MarkJ Over a year ago

+1. This is exactly what the VB.Net compiler does anyway - it simply automatically inserts the default values for any missing values when it compiles the caller.

Henk Holterman Over a year ago

@MarkJ, yes, but in Fx4 the optional values are also in the metadata, I just verified with VS2010. C# uses the opt values from VB just fine.

STW · Accepted Answer · 2010-03-03 13:07:36Z

2

Without using C# 4.0 (which adds support for optional parameters) you can't use them; if you run your code through FxCop you will see Optional parameters specifically flagged for their inability to be consumed by C#.

answered Mar 3, 2010 at 13:07

STW

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Comments

Andrey · Accepted Answer · 2010-03-03 13:13:05Z

0

if you want to retrieve optional parameters' values you can use reflection, this information is stored in custom attribute at corresponding parameter

answered Mar 3, 2010 at 13:13

Andrey

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1 Comment

jamone Over a year ago

I think you misunderstood the question. He wants to do SomeMethod(someGUID, "Some String") from C# where the VB Method Signature is as he indicated. Something that's not possible on C# < 4.0

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