C# 3.5 Optional and DefaultValue for parameters

Question

I am using C# .net 3.5 to build an application. I have been working with optional parameter attributes in .net 4.0 with no problems. I did notice that with 3.5 there is the option (workaround) to add the following attributes to your method like so:

    public static void MethodName(string name, [Optional][DefaultValue(null)]string placeHolder)
    {

    }

Even though I have added the attributes to the method, if I try and call it like so:

     MethodName("test");

The compiler will complain that it is looking for two parameters instead of one. Is it actually possible to do this using C# .net 3.5? Am I doing something wrong?

Same thing happen with us.Did you get any solution? – PrateekSaluja Mar 13 '12 at 08:15 — PrateekSaluja, Mar 13 '12 at 08:15

rotman · Accepted Answer · 2013-04-24T07:53:23.983

35

Optional parameters are C# 4.0 language feature so it doesn't matter which framework you are targeting, but you have to compile it using VS 2010 or newer.

Use this syntax in VS 2010 or newer:

public static void MethodName(string name, string placeHolder = null)
{
    // body
}

Or this in older one:

public static void MethodName(string name, string placeHolder)
{
    // body
}

public static void MethodName(string name)
{
    MethodName(name, null);
}

edited Apr 24 '13 at 07:53

answered Feb 25 '11 at 10:57

rotman

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Yeah, I tried setting the framework version to 3.5 in VS2010, but it still throws a compilation error. "Arguments Mismatch". – Deano Feb 25 '11 at 14:04
I was also looking for a way to do this without having to do it the old skool way - looks like I might have to! – Deano Feb 25 '11 at 14:05
In project properties go to build tab, advanced and set the language to C# 4.0. That should work even when .NET 3.5 framework is set. – rotman Feb 25 '11 at 14:32
I tried setting the framework version to 4 & 3.5 in VS2010, but it still throws a compilation error when I use it in VS2008. "Arguments Mismatch" – Deano Feb 25 '11 at 16:26
And oh - you mentioned you use it in VS2008. It can't work. Only VS2010 can compile C# 4.0 code. That's what I wrote in my answer. – rotman Feb 25 '11 at 19:10

score 6 · Answer 2 · answered Feb 25 '11 at 10:58

The Optional attribute has been available since C# 1.0, and is used when interoperating with external code, it has no effect on method calls in your own code.

As there is no optional parameters in C# 3, you can use overloading instead:

public static void MethodName(string name, string placeHolder) {
  ...
}

public static void MethodName(string name) {
  MethodName(name, null);
}

(Side note: There is no C# version 3.5, that is a framework version.)

score 4 · Answer 3 · edited Jun 20 '20 at 09:12

4

Take a look at the following StackOverflow thread: C# Optional Parameters in .net 3.5

No use in copy pasting everything which has been said there, as the thread covers pretty much everything. Good luck.

edited Jun 20 '20 at 09:12

Community

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answered Feb 25 '11 at 10:58

Jens

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Yeah, I did see that question - unfortunately I tried setting the framework version to 3.5 in VS2010, but it still throws a compilation error. "Arguments Mismatch" – Deano Feb 25 '11 at 14:05

C# 3.5 Optional and DefaultValue for parameters

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