Convert generic ienumerable to arraylist

Question

I need to convert the linq query from generic ienumerable to arraylist.

ArrayList myArrayList = new ArrayList();
         var b =
              (from myObj in myCollection
           select new myClass
           {
            Name = myObj.Name,
            ac = myObj.ac
           });

I have tried doing

b.Cast<ArrayList>();

but it is not working.

Edited : I got it working with @devdigital solution

but i will also want to point out that at same time i found a hackish solution.

myArrayList.InsertRange(0, b.ToArray());

The Cast<T> extension casts each element of an IEnumerable and returns them as another IEnumerable. It is therefore not useful to convert the collection itself. — Matthias Meid
– Matthias Meid, Commented Feb 14, 2012 at 12:23

devdigital · Accepted Answer · 2012-02-14 12:18:57Z

15

One of the constructors for the ArrayList type takes an ICollection, so you should be able to do the following:

var b =
    (from myObj in myCollection
     select new myClass
    {
      Name = myObj.Name,
      ac = myObj.ac
    }).ToArray();

ArrayList myArrayList = new ArrayList(b);

answered Feb 14, 2012 at 12:18

devdigital

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5 Comments

Matthias Meid Over a year ago

Doesn't ArrayList need an ICollection? msdn.microsoft.com/en-us/library/…

Matthias Meid Over a year ago

Yeah, but this is parameter-less. I wanted to point out that ArrayList(IEnumerable) does not exist.

devdigital Over a year ago

Yes, that's why b is converted to an array with ToArray(). System.Array implements ICollection. You could also use a List of course.

Matthias Meid Over a year ago

Oh, sorry! I missed this, this is my fault.

MakePeaceGreatAgain Over a year ago

Be aware that this will double the memory-allocations. First everything will be collected into the array, and afterwards the entire array is copied again into the ArrayList. However I can´t see any way around this.

Community · Accepted Answer · 2017-05-23 12:13:58Z

4

I'd suggest you to use a List<T> rather than an ArrayList. You can actually use the ToList extension method or the List's constructor which takes an IEnumerable<T>:

var myList = b.ToList(); // either
var myListTwo = new List<myClass>(b); // or

List<T> was newly introduced with .NET 2.0 and is generic. This means it yields you values of your actual type at compile-time, which is myClass, instead of object.

Edit: If you actually need an ArrayList, you need to copy b twice, as it cannot deal with IEnumerable directly, as devdigital pointed out in his reply:

ArrayList arrayList = new ArrayList(b.ToArray());

edited May 23, 2017 at 12:13

CommunityBot

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answered Feb 14, 2012 at 12:19

Matthias Meid

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1 Comment

devdigital Over a year ago

I'm assuming he needs an ArrayList for some legacy API.

Dennis Traub · Accepted Answer · 2012-02-14 12:19:41Z

2

You can convert your IEnumerable to an array with ToArray(), then construct an ArrayList from that array.

var b = (from myObj in myCollection
         select new myClass
         {
             Name = myObj.Name,
             ac = myObj.ac
         });
var myArrayList = new ArrayList(b.ToArray());

answered Feb 14, 2012 at 12:19

Dennis Traub

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Comments

Leila · Accepted Answer · 2012-02-14 12:24:30Z

0

ArrayList arrayList = new ArrayList(b.ToList());

answered Feb 14, 2012 at 12:24

Leila

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