interfaces in c#.net

30 Dec 2005 7:52 AM

saket

hello frnds if any one cud help me how to implement the concept of interface and interface objects in c#.net. if its not possible to expalin in mail..plz do send me some link where it is best explained Thanks

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30 Dec 2005 11:45 AM

Paul Henderson

You might get a better response posting this in a C#-specific group.
However...

An interface is a structure that declares certain methods and
properties (like a class), but doesn't provide implementations of them.
So, you can (almost) never create an instance of an interface with
'new', as it's meaningless - the resulting object can't actually *do*
anything.

Instead, you define a class that implements the interface - that is,
the interface name is included in its list of base classes, and the
class is then required by the compiler to implement all of the
functions declared in the interface.

The idea is that you can then define functions that take as a parameter
an object of arbitrary type, but which is known to implement the
interface (declaring a variable of interface type means it is a
reference to some object of a class implementing the interface); then,
you can use the methods that you know must exist in the class (those
defined in the interface) to do whatever you want, without concerning
yourself with what other methods/functionality the object may have.

So, for example, the IEnumerable interface in .NET is implemented by
collection classes, and it means that an object of any class
implementing it, regardless of how the collection itself actually
works, can be used as a 'foreach' variable and a few other things, as
the compiler then knows that the object passed is guaranteed to have
certain functionality.

To define your own interface, use the 'interface' keyword, and declare
the members like for a class (but without function bodies). Then, you
could have a function that takes as a parameter an object implementing
the interface, which could actually be an instance of any class you
write that implements the interface. e.g. [syntax may be *slightly*
wrong as I haven't tried compiling this]:

interface ISortable
{
    void SortData();
    bool IsSorted
    {
        get;
    }
}

class SomethingSortable : ISortable
{
    void SortData()    // if we don't override this function our class
won't compile
    {
        [...]
    }
    bool IsSorted
    {
        get
        {
              return ...;
        }
    }
}

Now we could have a method somewhere like this:

object BinarySearch(ISortable lst)
{
     lst.SortData();   // we know this method has to exist in any
object passed
}

Hope that helps...