在iOS中解析XML

以读文件的形式
iOS中的XML是event－driven模式
1：打开一个xml文件，读取内容到NSData中
2：调用NSXMLParse的nitWithData方法，并设置代理tweetParser.delegate = self;
3：调用回调函数
注意：xml文件的第一个tag必须要顶格写！
<?xml version="1.0"encoding="UTF-8"?>    
<bookstore>    
   <book catalog="Programming">    
       <title lang="en">C++ ProgrammingLanguage</title>    
       <author>Bjarne Stroustrup</author>    
       <year>1998</year>    
       <price>98.0</price>   
   </book>    
 <book catalog="Networking">    
       <title lang="en">TCP/IP Illustrated</title>    
       <author>Richard Stevens</author>    
       <year>1996</year>    
       <price>56.0</price>   
 </book>    
</bookstore>    
<?xml version="1.0"encoding="UTF-8"?> 
<bookstore> 
   <book catalog="Programming"> 
       <title lang="en">C++ Programming Language</title> 
       <author>Bjarne Stroustrup</author> 
       <year>1998</year> 
       <price>98.0</price> 
   </book> 
 <book catalog="Networking"> 
       <title lang="en">TCP/IP Illustrated</title> 
       <author>Richard Stevens</author> 
       <year>1996</year> 
       <price>56.0</price> 
 </book> 
</bookstore>