Initializing ArrayList with constant literal

Question

Can the ArrayList below be initialized directly without the need for aFileExt string array?

private static string[] aFileExt = 
     {"css", "gif", "htm", "html", "txt", "xml" };
private System.Collections.ArrayList alFileTypes =
     new System.Collections.ArrayList(aFileExt);

The line below is the goal, but my .Net Compiler does not like it:

private static System.Collections.ArrayList alFileTypes = 
     new System.Collections.ArrayList({"css","gif","htm","html","txt","xml"});

I am using the .net Micro Framework and thus do not have access to generic types.

score 73 · Accepted Answer · answered Nov 12 '09 at 15:38

73

C# 1 or 2:

private static ArrayList alFileTypes = 
     new ArrayList(new string[] {"css","gif","htm","html","txt","xml"});

C# 3 using an implicitly typed array:

private static ArrayList alFileTypes = 
    new ArrayList(new[] {"css","gif","htm","html","txt","xml"});

C# 3 using a collection initializer:

private static ArrayList alFileTypes = 
    new ArrayList{"css","gif","htm","html","txt","xml"};

Or create your own helper method:

public static ArrayList CreateList(params object[] items)
{
    return new ArrayList(items);
}

then:

static ArrayList alFileTypes = CreateList("css","gif","htm","html","txt","xml");

Any reason why you're not using the generic collections, btw?

answered Nov 12 '09 at 15:38

Jon Skeet

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Thanks for your help. Yes, generics and many of the System.Collections are not supported in my version of .net. – MandoMando Nov 12 '09 at 15:57
@MandoMando: For a question like this it's probably worth stating which version of .NET you're using, and which version of C#. – Jon Skeet Nov 12 '09 at 15:59
The C# 3 collection initializer is the solution for me because: 1. it compiles on my (special) version of .net 2. does not create a new object. (memory is an issue in this case) – MandoMando Nov 12 '09 at 16:03
Jon, I didn't mention my version of .net somewhat intentionally because it's in beta and changing, and there are very few folks around world that use netmf v4.0. – MandoMando Nov 12 '09 at 16:08
@MandoMando: It would still have been useful information. For example, if you knew you could use C# 3 features even without generics, that would have told us that a collection initializer would be a good way to go. – Jon Skeet Nov 12 '09 at 17:16
@Jon Skeet: Knowing the version info would have saved you time. I honestly cannot make any factual claims about the version of C# supported (it's up to MS .Net team to call that when they're ready). Though I did know that generics are not supported and thought it's unrelated. Based on the responses to my new-to-the-site post, I now know to include all helpful info :) Many thanks for providing solutions for all versions. Which was indeed what I was looking to feed the compiler. – MandoMando Nov 12 '09 at 17:42

score 15 · Answer 2 · answered Nov 12 '09 at 15:39

15

If you're using .NET 2.0 or greater, you should be using the generic List<T> type (even if it's List<object>, which would given you the same functionality as ArrayList).

If you're using .NET 3.5 or greater, you can use this syntax:

private static List<string> fileTypes = new List<string>()
{ 
    "css","gif","htm","html","txt","xml" 
};

Either way, however, if you want to stick with ArrayList, you can just do:

private static System.Collections.ArrayList alFileTypes = 
 new System.Collections.ArrayList(new object[] {"css","gif","htm","html","txt","xml"});

answered Nov 12 '09 at 15:39

Adam Robinson

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3

+1 for using List instead or ArrayList (and still answering the original question). – Guffa Nov 12 '09 at 15:45
Actually, my version of .Net Generics are not supported. – MandoMando Nov 12 '09 at 15:54

Thomas Levesque · Answer 3 · 2013-07-16T21:40:28.853

10

C# 3.0 with a generic List<T>, rather than an ArrayList :

private static List<string> alFileTypes =
    new List<string> {"css","gif","htm","html","txt","xml"};

edited Jul 16 '13 at 21:40

answered Nov 12 '09 at 15:41

Thomas Levesque

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Excellent! But to compile, the LHS would need to be of type List: `private static List alFileTypes = new List {"css", ...` – Brent Faust Jul 16 '13 at 21:16
@Rubistro, indeed... I just forgot to replace "ArrayList" ;) – Thomas Levesque Jul 16 '13 at 21:40

score 1 · Answer 4 · answered Nov 12 '09 at 15:38

1

private static System.Collections.ArrayList alFileTypes = 
 new System.Collections.ArrayList(new string [] {"css","gif","htm","html","txt","xml"});

answered Nov 12 '09 at 15:38

Sean Bright

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score 1 · Answer 5 · answered Nov 12 '09 at 15:40

1

Try

private static System.Collections.ArrayList alFileTypes =   new System.Collections.ArrayList(){"css","gif","htm","html","txt","xml"};

answered Nov 12 '09 at 15:40

TLiebe

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I thought this was clever, too. In my mind it didn't even look like it was going to compile :) thanks! – MandoMando Nov 12 '09 at 16:13

score 0 · Answer 6 · answered Nov 12 '09 at 15:38

yes, just change

private static System.Collections.ArrayList alFileTypes = 
     new System.Collections.ArrayList({"css","gif","htm","html","txt","xml"});

to

private static System.Collections.ArrayList alFileTypes = 
     new System.Collections.ArrayList(new string[] {"css","gif","htm","html","txt","xml"});

Initializing ArrayList with constant literal

6 Answers6