一：確認(rèn)網(wǎng)絡(luò)環(huán)境3G/WIFI 
 
    1. 添加源文件和framework 
     
    開發(fā)Web等網(wǎng)絡(luò)應(yīng)用程序的時(shí)候，需要確認(rèn)網(wǎng)絡(luò)環(huán)境，連接情況等信息。如果沒有處理它們，是不會(huì)通過Apple的審查的。 
    Apple 的 例程 Reachability 中介紹了取得/檢測網(wǎng)絡(luò)狀態(tài)的方法。要在應(yīng)用程序程序中使用Reachability，首先要完成如下兩部： 
     
    1.1. 添加源文件： 
    在你的程序中使用 Reachability 只須將該例程中的 Reachability.h 和 Reachability.m 拷貝到你的工程中。如下圖： 
 
     
     
    1.2.添加framework： 
    將SystemConfiguration.framework 添加進(jìn)工程。如下圖： 
     
     
    2. 網(wǎng)絡(luò)狀態(tài) 
     
    Reachability.h中定義了三種網(wǎng)絡(luò)狀態(tài)： 
    typedef enum { 
        NotReachable = 0,            //無連接 
        ReachableViaWiFi,            //使用3G/GPRS網(wǎng)絡(luò) 
        ReachableViaWWAN            //使用WiFi網(wǎng)絡(luò) 
    } NetworkStatus; 
     
    因此可以這樣檢查網(wǎng)絡(luò)狀態(tài)： 
 
    Reachability *r = [Reachability reachabilityWithHostName:@“ www.apple.com”]; 
    switch ([r currentReachabilityStatus]) { 
            case NotReachable: 
                    // 沒有網(wǎng)絡(luò)連接 
                    break; 
            case ReachableViaWWAN: 
                    // 使用3G網(wǎng)絡(luò) 
                    break; 
            case ReachableViaWiFi: 
                    // 使用WiFi網(wǎng)絡(luò) 
                    break; 
    } 
     
    3.檢查當(dāng)前網(wǎng)絡(luò)環(huán)境 
    程序啟動(dòng)時(shí)，如果想檢測可用的網(wǎng)絡(luò)環(huán)境，可以像這樣 
    // 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. 鏈接狀態(tài)的實(shí)時(shí)通知 
    網(wǎng)絡(luò)連接狀態(tài)的實(shí)時(shí)檢查，通知在網(wǎng)絡(luò)應(yīng)用中也是十分必要的。接續(xù)狀態(tài)發(fā)生變化時(shí)，需要及時(shí)地通知用戶： 
     
    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; 
 
    // 更新網(wǎng)絡(luò)狀態(tài) 
    - (void)updateStatus { 
        self.remoteHostStatus = [[Reachability sharedReachability] remoteHostStatus]; 
    } 
 
    // 通知網(wǎng)絡(luò)狀態(tài) 
    - (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]; 
        } 
    } 
 
    // 程序啟動(dòng)器，啟動(dòng)網(wǎng)絡(luò)監(jiān)視 
    - (void)applicationDidFinishLaunching:(UIApplication *)application { 
     
        // 設(shè)置網(wǎng)絡(luò)檢測的站點(diǎn) 
        [[Reachability sharedReachability] setHostName:@"www.apple.com"]; 
        [[Reachability sharedReachability] setNetworkStatusNotificationsEnabled:YES]; 
        // 設(shè)置網(wǎng)絡(luò)狀態(tài)變化時(shí)的通知函數(shù) 
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) 
                                                 name:@"kNetworkReachabilityChangedNotification" object:nil]; 
        [self updateStatus]; 
    } 
 
    - (void)dealloc { 
        // 刪除通知對象 
        [[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 { 
        // ... 
                   
        // 監(jiān)測網(wǎng)絡(luò)情況 
        [[NSNotificationCenter defaultCenter] addObserver:self 
                              selector:@selector(reachabilityChanged:) 
                              name: kReachabilityChangedNotification 
                              object: nil]; 
        hostReach = [[Reachability reachabilityWithHostName:@"www.google.com"] retain]; 
        hostReach startNotifer]; 
        // ... 
    } 
 
 
二：使用NSConnection下載數(shù)據(jù) 
     
    1.創(chuàng)建NSConnection對象，設(shè)置委托對象 
     
    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. 實(shí)現(xiàn)委托方法 
    - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { 
        // store data 
        [self.receivedData setLength:0];            //通常在這里先清空接受數(shù)據(jù)的緩存 
    } 
     
    - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { 
           /* appends the new data to the received data */ 
        [self.receivedData appendData:data];        //可能多次收到數(shù)據(jù)，把新的數(shù)據(jù)添加在現(xiàn)有數(shù)據(jù)最后 
    } 
 
    - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error { 
        // 錯(cuò)誤處理 
    } 
 
    - (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. 設(shè)置委托對象，開始解析 
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];   //或者也可以使用initWithContentsOfURL直接下載文件，但是有一個(gè)原因不這么做： 
    // 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.  應(yīng)用舉例 
    - (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{ 
        // 元素開始句柄 
        if (qName) { 
            elementName = qName; 
        } 
        if ([elementName isEqualToString:@"user"]) { 
            // 輸出屬性值 
            NSLog(@"Name is %@ , Age is %@", [attributeDict objectForKey:@"name"], [attributeDict objectForKey:@"age"]); 
        } 
    } 
 
    - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI  
                                        qualifiedName:(NSString *)qName 
    { 
        // 元素終了句柄 
        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];