Understanding of protocols and delegates in iOS

Http://www.cnblogs.com/hyzhou/archive/2012/12/10/2810861.html

See an article, feel the blogger wrote this parable special image.

The agreement is equivalent to a task table with tasks that must be completed, as well as optional tasks to complete. The delegate is equivalent to the individual who practices the task table.

Before I thought about why we had to use a delegate, the way to pass a value has global variables, expose class properties, and so on, the advantage of a possible delegate is that you can process the data while invoking the delegate and update the UI.

Can think of this, will be used, but the meaning is still unclear, there is a understanding of the predecessors also hope to teach one or two.

Understanding of protocols and delegates in iOS