NSURLConnection的方法说明
初始化一个NSURLConnectionNSURLConnection *registerConnection ＝ [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:[ NSURL URLWithString:@"http://www.baidu.com" ]] delegate:self];//我们可以从http返回的response中拿到一些连接的信息。这里我拿到了要下载的数据的大小，保存在"Content-Length"的字段中- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;//接受返回的data NSMutableData *receiveData ;[receiveData appendData:data];- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data//连接结束，一般再这里处理data- (void)connectionDidFinishLoading:(NSURLConnection *)connection//定义连接出错的情况的处理- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;