以下苹果开发网络编程知识由 CocoaChina 会员 “cocoa_yang” 总结，希望能为苹果开发新手梳理知识脉络，节省入门时间。 一：确认网络环境3G/WIFI 1. 添加源文件和framework 开发Web等网络应用程序的时候，需要确认网络环境，连接情况等信息。如果没有处理它们，是不会通过Apple的审查的。 Apple 的 例程 Reachability 中介绍了取得/检测网络状态的方法。要在应用程序程序中使用Reachability，首先要完成如下两部： 1.1. 添加源文件： 在你的程序中使用 Reachability 只须将该例程中的 Reachability.h 和 Reachability.m 拷贝到你的工程中。如下图： 1.2.添加framework： 将SystemConfiguration.framework 添加进工程。如下图： 2. 网络状态 Reachability.h中定义了三种网络状态： typedef enum { NotReachable = 0, //无连接 ReachableViaWiFi, //使用3G/GPRS网络 ReachableViaWWAN //使用WiFi网络 } NetworkStatus; 因此可以这样检查网络状态： Reachability *r = [Reachability reachabilityWithHostName:@“www.apple.com”]; switch ([r currentReachabilityStatus]) { case NotReachable: // 没有网络连接 break; case ReachableViaWWAN: // 使用3G网络 break; case ReachableViaWiFi: // 使用WiFi网络 break; } 3.检查当前网络环境
程序启动时，如果想检测可用的网络环境，可以像这样 // 是否wifi + (BOOL) IsEnableWIFI { return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable); } // 是否3G + (BOOL) IsEnable3G { return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable); } 例子： - (void)viewWillAppear:(BOOL)animated { if (([Reachability reachabilityForInternetConnection].currentReachabilityStatus == NotReachable) && ([Reachability reachabilityForLocalWiFi].currentReachabilityStatus == NotReachable)) { self.navigationItem.hidesBackButton = YES; [self.navigationItem setLeftBarButtonItem:nil animated:NO]; } } 4. 链接状态的实时通知
网络连接状态的实时检查，通知在网络应用中也是十分必要的。接续状态发生变化时，需要及时地通知用户： Reachability 1.5版本 // My.AppDelegate.h #import "Reachability.h" @interface MyAppDelegate : NSObject <UIApplicationDelegate> { NetworkStatus remoteHostStatus; } @property NetworkStatus remoteHostStatus; @end // My.AppDelegate.m #import "MyAppDelegate.h" @implementation MyAppDelegate @synthesize remoteHostStatus; // 更新网络状态 - (void)updateStatus { self.remoteHostStatus = [[Reachability sharedReachability] remoteHostStatus]; } // 通知网络状态 - (void)reachabilityChanged:(NSNotification *)note { [self updateStatus]; if (self.remoteHostStatus == NotReachable) { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:NSLocalizedString(@"AppName", nil) message:NSLocalizedString (@"NotReachable", nil) delegate:nil cancelButtonTitle:@"OK" otherButtonTitles: nil]; [alert show]; [alert release]; } } // 程序启动器，启动网络监视 - (void)applicationDidFinishLaunching:(UIApplication *)application { // 设置网络检测的站点 [[Reachability sharedReachability] setHostName:@"www.apple.com"]; [[Reachability sharedReachability] setNetworkStatusNotificationsEnabled:YES]; // 设置网络状态变化时的通知函数 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:@"kNetworkReachabilityChangedNotification" object:nil]; [self updateStatus]; } - (void)dealloc { // 删除通知对象 [[NSNotificationCenter defaultCenter] removeObserver:self]; [window release]; [super dealloc]; } Reachability 2.0版本 // MyAppDelegate.h @class Reachability; @interface MyAppDelegate : NSObject <UIApplicationDelegate> { Reachability *hostReach; } @end // MyAppDelegate.m - (void)reachabilityChanged:(NSNotification *)note { Reachability* curReach = [note object]; NSParameterAssert([curReach isKindOfClass: [Reachability class]]); NetworkStatus status = [curReach currentReachabilityStatus]; if (status == NotReachable) { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"AppName"" message:@"NotReachable" delegate:nil cancelButtonTitle:@"YES" otherButtonTitles:nil]; [alert show]; [alert release]; } } - (void)applicationDidFinishLaunching:(UIApplication *)application { // ... // 监测网络情况 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name: kReachabilityChangedNotification object: nil]; hostReach = [[Reachability reachabilityWithHostName:@"www.google.com"] retain]; hostReach startNotifer]; // ... } 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; } 三：使用NSXMLParser解析xml文件 1. 设置委托对象，开始解析 NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data]; //或者也可以使用initWithContentsOfURL直接下载文件，但是有一个原因不这么做： // It's also possible to have NSXMLParser download the data, by passing it a URL, but this is not desirable // because it gives less control over the network, particularly in responding to connection errors. [parser setDelegate:self]; [parser parse]; 2. 常用的委托方法 - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict; - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName; - (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string; - (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError; static NSString *feedURLString = @"http://www.yifeiyang.net/test/test.xml"; 3. 应用举例 - (void)parseXMLFileAtURL:(NSURL *)URL parseError:(NSError **)error { NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:URL]; [parser setDelegate:self]; [parser setShouldProcessNamespaces:NO]; [parser setShouldReportNamespacePrefixes:NO]; [parser setShouldResolveExternalEntities:NO]; [parser parse]; NSError *parseError = [parser parserError]; if (parseError && error) { *error = parseError; } [parser release]; } - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString*)qName attributes:(NSDictionary *)attributeDict{ // 元素开始句柄 if (qName) { elementName = qName; } if ([elementName isEqualToString:@"user"]) { // 输出属性值 NSLog(@"Name is %@ , Age is %@", [attributeDict objectForKey:@"name"], [attributeDict objectForKey:@"age"]); } } - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName { // 元素终了句柄 if (qName) { elementName = qName; } } - (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string { // 取得元素的text } NSError *parseError = nil; [self parseXMLFileAtURL:[NSURL URLWithString:feedURLString] parseError:&parseError];
