Order ArrayList by attribute object the ArrayList holds?

ArrayList is somewhat deprecated. We use the generic List<T> class now.*

You can sort a List<T> in-place using List<T>.Sort:

List<Person> persons = // ...

persons.Sort((a, b) => string.Compare(a.Name, b.Name));

or create a new List<T> using LINQ's Enumerable.OrderBy:

List<Person> persons = // ...

List<Person> sortedPersons = persons.OrderBy(p => p.Name).ToList();

(* Unless you're stuck with .NET Framework 1.1)

As dtb explained, you should probably use a generic List<T> than an untyped ArrayList unless you're using a pre 2.0 version of .NET.

If you really want to do it with an ArrayList, there are two way of doing it :

• if the elements of the collection implement IComparable, just use the Sort method with no arguments :

  arrayList.Sort();
  

• otherwise, you need to create a custom comparer by implementing the IComparer interface :

  public class PersonComparer : IComparer
  {
      public int Compare(object a, object b)
      {
          Person pa = a as Person;
          Person pb = b as Person;
          if (pa == pb) return 0;
          if (pa == null) return -1;
          if (pb == null) return 1;
          return string.Compare(pa.Name, pb.Name);
      }
  }
  
  ...
  
  arrayList.Sort(new PersonComparer());
  

Whenever you want to sort an array you need to compare it with a specific element of it. Suppose you have a List of array called Client and Client has clientID Now you want to sort it. Your code should be

Client.Sort(a, b) => string.Compare(a.clientID.ToString(), b.clientID.ToString()));