异步：
NSMutableData* buf = [[NSMutableData alloc] initWithLength:0];
NSURLConnection* connection = [[NSURLConnection alloc] initWithRequest:req delegate:self]; // 收到响应时, 会触发 - (void)connection:(NSURLConnection *)aConnection didReceiveResponse:(NSURLResponse *)aResponse; // 你可以在里面判断返回结果, 或者处理返回的http头中的信息 // 每收到一次数据, 会调用一次 - (void)connection:(NSURLConnection *)aConn didReceiveData:(NSData *)data; // 因此一般来说,是 - (void)connection:(NSURLConnection *)aConn didReceiveData:(NSData *)data { [buf appendData:data]; } // 当然buffer就是前面initWithRequest时同时声明的. // 网络错误时触发 - (void)connection:(NSURLConnection *)aConn didFailWithError:(NSError *)error; // 全部数据接收完毕时触发 - (void)connectionDidFinishLoading:(NSURLConnection *)aConn; ,~ // 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]; 异步请求代码 // .h file: // // DownloadHelper.h // BigViewApp // // Created by lu Yinghuai on 11-2-14. // Copyright 2011 minesage. All rights reserved. // #import < Foundation / Foundation.h > @protocol DownloadHelperDelegate;@interface DownloadHelper : NSObject { @private NSURLConnection * appListFeedConnection; NSMutableData * appListData; NSString * strResultData; id < DownloadHelperDelegate > delegate ;} - (id)initWithDelegate: (id < DownloadHelperDelegate > )theDelegate; - ( void ) startDownload: (NSString * ) targetUrl; @property (nonatomic, assign) id < DownloadHelperDelegate > delegate ;@property (nonatomic, retain) NSURLConnection * appListFeedConnection;@property (nonatomic, retain) NSMutableData * appListData;@property (nonatomic, retain) NSString * strResultData;@end@protocol DownloadHelperDelegate - ( void )didFinishDownload:(NSString * ) strResult; - ( void )downloadErrorOccurred:(NSError * ) error;@end // .m file // // DownloadHelper.m // BigViewApp // // Created by lu Yinghuai on 11-2-14. // Copyright 2011 minesage. All rights reserved. // #import " DownloadHelper.h " @implementation DownloadHelper@synthesize appListFeedConnection, appListData, delegate ,strResultData; - (id)initWithDelegate:(id < DownloadHelperDelegate > )theDelegate{ self = [super init]; if (self != nil) { self. delegate = theDelegate; // strResultData = [[NSString alloc] init]; } return self;} - ( void ) startDownload: (NSString * ) targetUrl { NSURLRequest * urlRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:targetUrl]]; self.appListFeedConnection = [[[NSURLConnection alloc] initWithRequest:urlRequest delegate :self] autorelease]; // Test the validity of the connection object. The most likely reason for the connection object // to be nil is a malformed URL, which is a programmatic error easily detected during development // If the URL is more dynamic, then you should implement a more flexible validation technique, and // be able to both recover from errors and communicate problems to the user in an unobtrusive manner. // NSAssert(self.appListFeedConnection != nil, @" Failure to create URL connection. " ); // show in the status bar that network activity is starting [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;} #pragma mark - #pragma mark NSURLConnection delegate methods // ------------------------------------------------------------------------------- // handleError:error // ------------------------------------------------------------------------------- - ( void )handleError:(NSError * )error{ /* NSString *errorMessage = [error localizedDescription]; UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Cannot Show Top Paid Apps" message:errorMessage delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil]; [alertView show]; [alertView release]; */ [ delegate downloadErrorOccurred:error];} // The following are delegate methods for NSURLConnection. Similar to callback functions, this is how // the connection object, which is working in the background, can asynchronously communicate back to // its delegate on the thread from which it was started - in this case, the main thread. // // ------------------------------------------------------------------------------- // connection:didReceiveResponse:response // ------------------------------------------------------------------------------- - ( void )connection:(NSURLConnection * )connection didReceiveResponse:(NSURLResponse * )response{ self.appListData = [NSMutableData data]; // start off with new data } // ------------------------------------------------------------------------------- // connection:didReceiveData:data // ------------------------------------------------------------------------------- - ( void )connection:(NSURLConnection * )connection didReceiveData:(NSData * )data{ [appListData appendData:data]; // append incoming data } // ------------------------------------------------------------------------------- // connection:didFailWithError:error // ------------------------------------------------------------------------------- - ( void )connection:(NSURLConnection * )connection didFailWithError:(NSError * )error{ [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; if ([error code] == kCFURLErrorNotConnectedToInternet) { // if we can identify the error, we can present a more precise message to the user. NSDictionary * userInfo = [NSDictionary dictionaryWithObject: @" No Connection Error " forKey:NSLocalizedDescriptionKey]; NSError * noConnectionError = [NSError errorWithDomain:NSCocoaErrorDomain code:kCFURLErrorNotConnectedToInternet userInfo:userInfo]; [self handleError:noConnectionError]; } else { // otherwise handle the error generically [self handleError:error]; } self.appListFeedConnection = nil; // release our connection } // ------------------------------------------------------------------------------- // connectionDidFinishLoading:connection // ------------------------------------------------------------------------------- - ( void )connectionDidFinishLoading:(NSURLConnection * )connection{ self.appListFeedConnection = nil; // release our connection [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; strResultData = [[NSString alloc] initWithData:appListData encoding:NSASCIIStringEncoding]; NSLog( @" %@ " ,strResultData); [ delegate didFinishDownload:strResultData]; self.appListData = nil;} // ------------------------------------------------------------------------------- // dealloc // ------------------------------------------------------------------------------- - ( void )dealloc{ [appListFeedConnection release]; [appListData release]; [strResultData release]; [super dealloc];}@end // .m 调用代码 １ .实例化： // download 排行榜 downLoadHelper = [[DownloadHelper alloc] initWithDelegate:self]; ２ . // 下载排行榜数据 [downLoadHelper startDownload: @" http://www.google.com/trends/hottrends/atom/hourly " ]; ３ .委托对象回调方法 #pragma mark ------ DownloadHelper Delegate Method ------ - ( void ) didFinishDownload:(NSString * ) strResult{ NSLog( @" didFinishDownload " ); [hotTrend.keyWordRecordList removeAllObjects]; NSLog( @" %@ " ,strResult);} - ( void ) downloadErrorOccurred:(NSError * ) error{ NSLog( @" downloadErrorOccurred " );}第二段是同步请求
