ICollection to string[]

Question

I have a object of type ICollection<string>. What is the best way to convert to string[].

How can this be done in .NET 2?
How can this be done cleaner in later version of C#, perhaps using LINQ in C# 3?

score 35 · Accepted Answer · edited Oct 05 '13 at 02:49

35

You could use the following snippet to convert it to an ordinary array:

string[] array = new string[collection.Count];
collection.CopyTo(array, 0);

That should do the job :)

edited Oct 05 '13 at 02:49

bryanbcook

answered Nov 30 '08 at 11:40

AdrianoKF

do i need to initialize the array with the right size first .. cant i just do this: string[] futures = new string[] {}; FutureFVDictionary.Keys.CopyTo(futures, 0); ; – leora Nov 30 '08 at 11:54
1

The array must first be initialized to the correct size - otherwise CopyTo will fail with an ArgumentException. – AdrianoKF Nov 30 '08 at 12:06
with List(mycoll).ToArray() you don't have to worry about size. – gimel Nov 30 '08 at 12:40
@AdrianoKF The first line should be `string[] array = new string[collection.Count];`, since `ICollection` has a [`Count`](http://msdn.microsoft.com/en-us/library/5s3kzhec.aspx) property. – Paolo Moretti Mar 30 '12 at 09:59

score 8 · Answer 2 · answered Nov 30 '08 at 11:44

8

If you're using C# 3.0 and .Net framework 3.5, you should be able to do:

ICollection<string> col = new List<string>() { "a","b"};
string[] colArr = col.ToArray();

of course, you must have "using System.Linq;" at the top of the file

answered Nov 30 '08 at 11:44

CVertex

Also List has a ToArray method since .NET 2.0, so if you're using List you don't need System.Linq – Cameron MacFarland Nov 30 '08 at 12:13
6

He asked for ICollection – CVertex Nov 30 '08 at 16:38
1

This is the best answer in my opinion – reggaeguitar Oct 20 '15 at 21:24

gimel · Answer 3 · 2008-11-30T12:18:31.810

7

In the (trivial) case of ICollection<String>, use ToArray:

String[] GetArray(ICollection<String> mycoll)
{
    return mycoll.ToArray<String>();
}

EDIT: with .Net 2.0, you can return the array with an extra List<String>:

String[] GetArray(ICollection<String> mycoll)
{
    List<String> result = new List<String>(mycoll);
    return result.ToArray();
}

edited Nov 30 '08 at 12:18

answered Nov 30 '08 at 11:43

gimel

The compiler can infer the type argument, so mycoll.ToArray() would be fine, without needing the part. – Daniel Earwicker Nov 30 '08 at 11:46
1

The List.ToArray method uses an array copy, so doing the array copy directly would be the better option than creating a list, which is another object. – Cameron MacFarland Nov 30 '08 at 12:27
1

List(mycoll).ToArray() abstracts the array creation and copying details. – gimel Nov 30 '08 at 12:38

3 Answers3