iphone 学习 - 读取数据

同步（会阻塞）
NSURLConnection 类：
+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error;

异步：（需要实现delegate）
NSURLConnection 类：
+ (NSURLConnection *)connectionWithRequest:(NSURLRequest *)request delegate:(id)delegate;
delegate 方法：
接收数据：
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
http load完成：
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;

利用这些就可以完成http 后台loading了