How to update an ArrayList?

Jason Anderson

I have an ArrayList that I enumerate through and want to update a property (Class1 property) within the ArrayList.

arrayList = new ArrayList();
Class1 class1 = new Class1();
...
...
arrayList.Add(class1);
...
...
Class1 temp;
IEnumerator ie = arrayList.GetEnumerator();
while (ie.MoveNext())
{
...
...
...
temp = (Class1)ie.Current;
temp.PropertyA = Convert.ToInt32(objDataReader.GetValue(6));
...
...
...
}

I want arrayList to reflect the value change of PropertyA.

The value is updated in temp, but not in arrayList.

Thanks for your help.

Jason

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes15y ago
Accepted answer
Actually, it works fine with an ArrayList as well:

using System;
using System.Collections;

class Class1
{
public int PropertyA {get; set;}
}

class Test
{
static void Main()
{
var arrayList = new ArrayList();
Class1 class1 = new Class1();
class1.PropertyA = 3;
arrayList.Add(class1);

Class1 temp;
IEnumerator ie = arrayList.GetEnumerator();
while (ie.MoveNext())
{
temp = (Class1)ie.Current;
temp.PropertyA = Convert.ToInt32("6");
}

Console.WriteLine(((Class1)arrayList[0]).PropertyA); // 6, not 3
Console.ReadKey();
}
}
0
Vulpes15y ago
Like you, Andrew, I don't use ArrayList or Hashtable any more. I prefer the generic alternatives as there's no need for any casting or (in the case of value types) boxing.
0
Andrew Fenster15y ago
Sure enough.

I didn't try it, but I was guessing that the reference got lost somehow when you cast the item. I haven't used an ArrayList even once since .Net 2.0 came out with generic collection classes.
0
Andrew Fenster15y ago
If you replaced your ArrayList with a List, I think it would work just fine. Here is your slightly revised code:

List myList = new List();
Class1 class1 = new Class1();
...
myList .Add(class1);
...
Class1 temp;
IEnumerator ie = myList.GetEnumerator();
while (ie.MoveNext())
{
...
temp = ie.Current;
temp.PropertyA = Convert.ToInt32(objDataReader.GetValue(6));
...
}
0