Question

suppose I have a class like

class ABC
{
    int ID;
    public string Name;
    public ABC(int i, string str) { ID = i; Name = str; }
}

And declare a array of class ABC.
Assume that I have also initialized each element using new keyword.
Now I want access element of class using it’s member ID instead of 0 based index. Make ID public if required.

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        ABC[] a = new ABC[3];
        a[0] = new ABC(100, "First");
        a[1] = new ABC(101, "Second");
        a[2] = new ABC(102, "Third");

        ABC newobj = a[100]; // where 100 is ID of class ABC
    }
}

class ABC
{
    int ID;
    string Name;
    public ABC(int i, string str)
    {
         ID = i;
         Name = str;
    }
}

Answer 1

Overloading the indexer on a standard array isn’t possible in C#. If you have to go the indexer route I’d suggest using Dictionary or a List class that supplies it’s own indexer.

class ABCCollection : List<ABC>
{
  public ABC this[int id]
  {
    get { return this.Where(abc => abc.ID == id).FirstOrDefault(); }
  }
}

Then you call use ABCCollection[100] to access your item.