How can you use optional parameters in C#?

Question

^{Note: This question was asked at a time when C# did not yet support optional parameters (i.e. before C# 4).}

We\'re building a web API tha

Answer 1

You can try this too
Type 1
public void YourMethod(int a=0, int b = 0) { //some code }

Type 2
public void YourMethod(int? a, int? b) { //some code }

Answer 2

I had to do this in a VB.Net 2.0 Web Service. I ended up specifying the parameters as strings, then converting them to whatever I needed. An optional parameter was specified with an empty string. Not the cleanest solution, but it worked. Just be careful that you catch all the exceptions that can occur.

Answer 3

optional parameters are nothing but default parameters! i suggest you give both of them default parameters. GetFooBar(int a=0, int b=0) if you don't have any overloaded method, will result in a=0, b=0 if you don't pass any values,if you pass 1 value, will result in, passed value for a, 0 and if you pass 2 values 1st will be assigned to a and second to b.

hope that answers your question.

Answer 4

Another option is to use the params keyword

public void DoSomething(params object[] theObjects)
{
  foreach(object o in theObjects)
  {
    // Something with the Objects…
  }
}

Called like...

DoSomething(this, that, theOther);

Answer 5

Hello Optional World

If you want the runtime to supply a default parameter value, you have to use reflection to make the call. Not as nice as the other suggestions for this question, but compatible with VB.NET.

using System;
using System.Runtime.InteropServices;
using System.Reflection;

namespace ConsoleApplication1
{
    class Class1
    {
        public static void sayHelloTo(
            [Optional,
            DefaultParameterValue("world")] string whom)
        {
            Console.WriteLine("Hello " + whom);
        }

        [STAThread]
        static void Main(string[] args)
        {
            MethodInfo mi = typeof(Class1).GetMethod("sayHelloTo");
            mi.Invoke(null, new Object[] { Missing.Value });
        }
    }
}

Answer 6

An easy way which allows you to omit any parameters in any position, is taking advantage of nullable types as follows:

public void PrintValues(int? a = null, int? b = null, float? c = null, string s = "")
{
    if(a.HasValue)
        Console.Write(a);
    else
        Console.Write("-");

    if(b.HasValue)
        Console.Write(b);
    else
        Console.Write("-");

    if(c.HasValue)
        Console.Write(c);
    else
        Console.Write("-");

    if(string.IsNullOrEmpty(s)) // Different check for strings
        Console.Write(s);
    else
        Console.Write("-");
}

Strings are already nullable types so they don't need the ?.

Once you have this method, the following calls are all valid:

PrintValues (1, 2, 2.2f);
PrintValues (1, c: 1.2f);
PrintValues(b:100);
PrintValues (c: 1.2f, s: "hello");
PrintValues();

When you define a method that way you have the freedom to set just the parameters you want by naming them. See the following link for more information on named and optional parameters:

Named and Optional Arguments (C# Programming Guide) @ MSDN