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
– PrateekSaluja

2012-03-13 08:15:04 +00:00
Commented Mar 13, 2012 at 8:15 — PrateekSaluja
– PrateekSaluja, Commented Mar 13, 2012 at 8:15

rotman · Accepted Answer · 2013-04-24 07:53:23Z

36

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, 2013 at 7:53

answered Feb 25, 2011 at 10:57

rotman

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5 Comments

Deano Over a year ago

Yeah, I tried setting the framework version to 3.5 in VS2010, but it still throws a compilation error. "Arguments Mismatch".

Deano Over a year ago

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!

rotman Over a year ago

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.

Deano Over a year ago

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"

rotman Over a year ago

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.

Guffa · Accepted Answer · 2011-02-25 10:58:21Z

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.)

Community · Accepted Answer · 2020-06-20 09:12:55Z

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, 2020 at 9:12

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answered Feb 25, 2011 at 10:58

Jens

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1 Comment

Deano Over a year ago

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"

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