Question

Since i am new to c#, would like to know about Interfaces and Delegates in c#, the difference between them and scenarios both these to be used. Please don’t provide any links, i would like an explanation in simple words.

Answer 1

A quote from C# in Nutshell.

A problem that can be solved with a delegate can also be solved with an
interface. For instance, the following explains how to solve our filter problem using
an ITransformer interface:

public interface ITransformer
{
   int Transform (int x);
}
public class Util
{
   public static void TransformAll (int[] values, ITransformer t)
   {
      for (int i = 0; i < values.Length; i++)
         values[i] = t.Transform (values[i]);
   }
}

class Squarer : ITransformer
{
   public int Transform (int x) { return x * x; }
}

...
static void Main()
{
   int[] values = { 1, 2, 3 };
   Util.TransformAll (values, new Squarer());
   foreach (int i in values)
      Console.WriteLine (i);
}

A delegate design may be a better choice than an interface design if one or more of
these conditions are true:

• The interface defines only a single
  method.
• Multicast capability is needed.
• The subscriber needs to implement the
  interface multiple times.

In the ITransformer example, we don’t need to multicast. However, the interface
defines only a single method. Furthermore, our subscriber may need to implement
ITransformer multiple times, to support different transforms, such as square or cube.
With interfaces, we’re forced into writing a separate type per transform, since Test
can implement ITransformer only once. This is quite cumbersome:

class Squarer : ITransformer
{
   public int Transform (int x) { return x * x; }
}
class Cuber : ITransformer
{
   public int Transform (int x) {return x * x * x; }
}
...
static void Main()
{
   int[] values = { 1, 2, 3 };
   Util.TransformAll (values, new Cuber());
   foreach (int i in values)
   Console.WriteLine (i);
}

And here is the code with delegate

public delegate int Transformer (int x);
class Util
{
   public static void Transform (int[] values, Transformer t)
   {
      for (int i = 0; i < values.Length; i++)
      values[i] = t (values[i]);
   }
}
class Test
{
   static void Main()
   {
      int[] values = { 1, 2, 3 };
      Util.Transform (values, Square); // Dynamically hook in Square
      foreach (int i in values)
         Console.Write (i + " "); // 1 4 9
   }
   static int Square (int x) { return x * x; }
}