Enumerate an object in an ArrayList by index

Michael Cort

I have an ArrayList of objects. This is sort of a quick and dirty thing, so the objects are not a class, just defined by a statement like

struct mp3
    {
        public string FileNm;
        public int RecNum ;
        ...

     }

My question is can I access the individual elements of the object using an index rather that name?

For example, instead of ArrayList1[44].FileNm I want to use ArrayList1[44][0] or something like that.

This is so I can use a loop to quickly go through all elements of the struct.

3 Replies

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Vulpes14y ago
Just as a matter of interest, you could do something like you wanted if you were to use a generic List rather than an ArrayList and add an indexer to your struct.

Here's a simple example I've just thrown together:

using System;
using System.Collections.Generic;

struct mp3
{
public string FileNm;
public int RecNum ;

// ...

public object this[int index]
{
get
{
switch(index)
{
case 0:
return FileNm;

case 1:
return RecNum;

default:
return null;
}
}

set
{
switch(index)
{
case 0:
FileNm = (string)value;
return;
case 1:
RecNum = (int)value;
return;
}
}
}

public override string ToString()
{
return String.Format("FileNm = {0}, RecNum = {1}", FileNm, RecNum);
}
}

class Test
{
static void Main()
{
List list = new List();
mp3 item = new mp3();
item.FileNm = "1";
item.RecNum = 2;
list.Add(item);
Console.WriteLine(list[0][0]);
Console.WriteLine(list[0][1]);
Console.ReadKey();
}
}

If list were an ArrayList instead, then you'd need to cast to mp3 before you could apply the indexer which makes the code rather ugly:

Console.WriteLine(((mp3)list[0])[0]);
Console.WriteLine(((mp3)list[0])[1]);
Michael Cort14y ago
Thanks. That will work since I am using it for debugging really.
Vulpes14y ago
No, it's not possible to do that but if you override the ToString method in your struct it makes it easier to enumerate the ArrayList:

struct mp3
{
public string FileNm;
public int RecNum ;

// ...

public override string ToString()
{
return String.Format("FileNm = {0}, RecNum = {1}", FileNm, RecNum);
}
}

foreach(mp3 item in ArrayList1) Console.WriteLine(item);