C#

BOOL EnumWindows(
    WNDENUMPROC lpEnumFunc,
    LPARAM lParam
);

BOOL CALLBACK EnumWindowsProc(
    HWND hwnd,
    LPARAM lParam
);

BOOL IsWindowVisible( 
    HWND hWnd
);

class DelegateExample {
    private List<IntPtr> windowList;

    public List<IntPtr> GetVisibleWindowHandles() {
        windowList=new List<IntPtr>();
        EnumWindows(new EnumWindowsProc(CollectVisibleWindows), IntPtr.Zero);
        Console.WriteLine("There are {0} visible windows", windowList.Count);
        return windowList;
    }

    private bool CollectVisibleWindows(IntPtr hWnd, IntPtr lParam) {
        if(IsWindowVisible(hWnd)) windowList.Add(hWnd);
        return true;  // please continue enumeration !
    }

    [DllImport("user32.dll")]
    private static extern int EnumWindows(LP_EnumWindowsProc ewp, IntPtr lParam); 

    private delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

    [DllImport("user32.dll")]
    private static extern bool IsWindowVisible(IntPtr hWnd);
}

Programm3r wrote:

link does not work

0x0000: 00 00 01 00 01 00 00 00 00 00 01 00 20 00 d2 d9 
0x0010: 00 00 16 00 00 00 89 50 4e 47 0d 0a 1a 0a 00 00 
0x0020: 00 0d 49 48 44 52 00 00 01 00 00 00 01 00 08 06 

Bitmap bmp;
using (var ms = new MemoryStream())
{
    icon.Save(ms);
    bmp = (Bitmap)Image.FromStream(ms);
}

public class Emp
{
   private int myID;
   public int ID
   {
      get { return myID; }
      set { myID = value; }
   }

   private string myName;
   public string Name
   {
      get { return myName; }
      set { myName = value; }
   }

   public static List<Emp> GetEmployees()
   {
      //return a list of emp objects
   }
}

//Using var allows type returned by GetEmployees to be 
//any thing that implements IEnumerable<T>
var emps = Emp.GetEmployees(); //Fill the list
foreach (Emp emp in emps.OrderBy(e => e.Name))
{
   Console.WriteLine(emp);
}

foreach (Emp emp in emps.OrderBy(e => e.ID))
{
   Console.WriteLine(emp);
}