Delegate

dele gate     （delegator gives tasks to another delegate objects to handle）

The delegation pattern is a design pattern whereby an object (the delegator) delegates one or more tasks to another delegate object. The tasks are encapsulated in the method(s) of the delegate object. When necessary, the delegator invokes the appropriate method on the delegate object, providing any required parameters. 

Delegator，Delegating Object；

v.s.

Delegate Object

Examples：

The delegation pattern is a design pattern whereby an object (the delegator) delegates one or more tasks to another delegate object. The tasks are encapsulated in the method(s) of the delegate object. When necessary, the delegator invokes the appropriate method on the delegate object, providing any required parameters. Many Foundation Framework classes implement the delegation pattern to enable custom error handling. The delegating Foundation object invokes a method on a delegate object (custom code that you implement) that includes an error object as a parameter.

The NSURLConnectionDelegate protocol declares a delegation method (connection:didFailWithError:) that returns an error object:

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;

This protocol is used for asynchronously loading a URL request via an NSURLConnection object. Your code implements a delegate object that conforms to this protocol and sets it as the delegate of theNSURLConnection object. Your code then loads the URL request asynchronously, and if an error occurs, the delegating (NSURLConnection) object invokes the connection:didFailWithError:method on your delegate object.