iOS 网络编程小结

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];