NSURLConnection详解

来源:http://blog.csdn.net/paulluo0739/article/details/6843312

URLRequest 的一个实例:(获取北京的天气情况)

- (void)weather {NSURL *url = [NSURL URLWithString:@"http://www.weather.com.cn/adat/cityinfo/101010100.html"];NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:10.0];NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];        //可以用代理方式实现<span>                //NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:request delegate:self];<pre name="code" class="cpp">NSDictionary *weatherDict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];NSDictionary *weatherInfo = [weatherDict objectForKey:@"weatherinfo"];NSString *city = [weatherInfo objectForKey:@"city"];NSString *weather = [weatherInfo objectForKey:@"weather"];NSLog(@"city:%@ weather:%@",city,weather);}

其中：

NSURLRequest默认的cache policy是NSURLRequestUseProtocolCachePolicy,是最能保持一致性的协议。

NSURLRequestReloadIgnoringCacheData 忽略缓存直接从原始地址下载

NSURLRequestReturnCacheDataElseLoad 只有在cache中不存在data时才从原始地址下载

NSURLRequestReturnCacheDataDontLoad 允许app确定是否要返回cache数据，如果使用这种协议当本地不存在response的时候，创建NSURLConnection or NSURLDownload实例时将会马上返回nil；这类似于离线模式，没有建立网络连接；

你只需要实现以下delegate方法来处理数据响应

- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSHTTPURLResponse*)response- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data- (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error- (void)connectionDidFinishLoading:(NSURLConnection *)connection

NSURLConnect还提供了一个方便的类方法(class method) : sendSynchronousRequest:returningResponse:error:可用来 同步地加载一个URL请求

+ (NSData *)sendSynchronousRequest:    (NSURLRequest *)request      returningResponse:   (NSURLResponse **)response    error:  (NSError **)error

• request 要装载的URL请求. 这个request 对象 作为初始化进程的一部分,被深度复制(deep-copied). 在这个方法返回之后, 再修改request, 将不会影响用在装载的过程中的request
• reponse 输出参数, 由服务器返回的URL响应
• error   输出参数, 如果在处理请求的过程中发生错误,就会使用.  无错误,就为NULL

一个实现异步get请求的例子:

- (void)setURLRequest_connection {    NSString *url = [NSString stringWithFormat:@"http://localhost/chat/messages.php?past=%ld&t=%ld",lastId, time(0)];            NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];      [request setURL:[NSURL URLWithString:url]];      [request setHTTPMethod:@"GET"];        NSURLConnection *conn=[[NSURLConnection alloc] initWithRequest:request delegate:self];        if (conn)      {            receivedData = [[NSMutableData data] retain];        }     }  - (void)timerCallback {      //[timer release];      [self getNewMessages];  }    - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response    {        [receivedData setLength:0];    }      - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data    {        [receivedData appendData:data];    }      - (void)connectionDidFinishLoading:(NSURLConnection *)connection    {        if (chatParser)          [chatParser release];            if ( messages == nil )          messages = [[NSMutableArray alloc] init];        chatParser = [[NSXMLParser alloc] initWithData:receivedData];      [chatParser setDelegate:self];//set the delegate      [chatParser parse];//start parse        [receivedData release];              [messageList reloadData];            NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[self methodSignatureForSelector: @selector(timerCallback)]];      [invocation setTarget:self];      [invocation setSelector:@selector(timerCallback)];      //timer = [NSTimer scheduledTimerWithTimeInterval:5.0 invocation:invocation repeats:NO];      [NSTimer scheduledTimerWithTimeInterval:5.0 invocation:invocation repeats:NO];//if set yes,then very 5 seconds updata the table  }

一个实现同步Get请求的例子：

    // 初始化请求      NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];               // 设置URL      [request setURL:[NSURL URLWithString:urlStr]];      // 设置HTTP方法      [request setHTTPMethod:@"GET"];      // 发 送同步请求, 这里得returnData就是返回得数据了      NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];       // 释放对象      [request release];  

更多详细信息请参见苹果开发文档：

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLConnection.html