iPhone：苹果开发网络编程知识总结 使用NSConnection下载数据

　　二：使用NSConnection下载数据

　　1.创建NSConnection对象，设置委托对象

　　NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self urlString]]];

　　[NSURLConnection connectionWithRequest:request delegate:self];

　　2. NSURLConnection delegate委托方法

　　- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;

　　- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;

　　- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;

　　- (void)connectionDidFinishLoading:(NSURLConnection *)connection;

　　3. 实现委托方法

　　- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {

　　// store data

　　[self.receivedData setLength:0]; //通常在这里先清空接受数据的缓存

　　}

　　- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

　　/* appends the new data to the received data */

　　[self.receivedData appendData:data]; //可能多次收到数据，把新的数据添加在现有数据最后

　　}

　　- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {

　　// 错误处理

　　}

　　- (void)connectionDidFinishLoading:(NSURLConnection *)connection {

　　// disconnect

　　[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

　　NSString *returnString = [[NSString alloc] initWithData:self.receivedData encoding:NSUTF8StringEncoding];

　　NSLog(returnString);

　　[self urlLoaded:[self urlString] data:self.receivedData];

　　firstTimeDownloaded = YES;

　　}