iOS: How to use "Block"

"Block"是很有用的东东，它实际上就是一个Closure，类似于javascript的closure, java中的匿名listener等。

参看

http://blog.sina.com.cn/s/blog_67419c420100vl8b.html

http://hechien.posterous.com/block-in-objective-c-20

http://mobile.51cto.com/iphone-279757.htm

http://popcornylu.blogspot.com/2011/08/objective-c-block.html

http://pragmaticstudio.com/blog/2010/7/28/ios4-blocks-1