ios网络编程

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，须要确认网络环境，链接状况等信息。若是没有处理它们，是不会经过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，首先要完成以下两部： 
     
    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。以下图： 
 
     
     
    1.2.添加framework： 
    将SystemConfiguration.framework 添加进工程。以下图： 
     
     
    2. 网络状态 
     
    Reachability.h中定义了三种网络状态： 
    typedef enum { 
        NotReachable = 0,            //无链接 
        ReachableViaWiFi,            //使用3G/GPRS网络 
        ReachableViaWWAN            //使用WiFi网络 
    } NetworkStatus; 
     
    所以能够这样检查网络状态： 
 
    Reachability *r = [Reachability reachabilityWithHostName:@“ www.apple.com”]; 
    switch ([r currentReachabilityStatus]) { 
            case NotReachable: 
                    // 没有网络链接 
                    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，若是想检测可用的网络环境，能够像这样 
    // 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. 连接状态的实时通知 
    网络链接状态的实时检查，通知在网络应用中也是十分必要的。接续状态发生变化时，须要及时地通知用户： 
     
    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 { 
        // ... 
                   
        // 监测网络状况 
        [[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.建立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];            //一般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];        //可能屡次收到数据，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];   //或者也可使用initWithContentsOfURL直接下载文件，可是有一个缘由不这么作： 
    // 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. 经常使用的委托方法 
    - (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];

使用NSOperation和NSOperationQueue启动多线程

在app store中的不少应用程序很是的笨重，他们有好的界面，但操做性不好，好比说当程序从网上或本地载入数据的时候，界面被冻结了，用户只能等程序彻底载入数据以后才能进行操做。  当 打开一个应用程序时，iphone会产生一个包含main方法的线程，所用程序中的界面都是运行在这个线程之中的（table views, tab bars, alerts…）,有时候咱们会用数据填充这些view，如今问        题是如何有效的载入数据，而且用户还能自如的操做程序。方法是启动新的线 程，专门用于数据的下载，而主线程不会由于下载数据被阻塞。  无论使用任何编程语言，在实现多线程时都是一件很麻烦的事情。更糟糕的是，一旦出 错，这种错误一般至关糟糕。然而，幸运的是apple从os x10.5在这方面作了不少的改进，NSThread的引入，使得开发多线程应用程序容易多了。除此以外，它们还引入了两个全新的 类，NSOperation和NSOperationQueue。  接下来咱们经过一个实例来剖析如何使用这两个类实现多线程。这里指示展现这两个类的基本用法，固然这不是使用他们的惟一办法。  如 果你熟悉java或者它的别的变种语言的话 ，你会发现NSOperation对象很像java.lang.Runnable接口，就像java.lang.Runnable接口那 样，NSOperation类也被设计为可扩展的，并且只有一个须要重写的方法。它就是－(void)main。使用NSOperation的最简单的方 式就是把一个NSOperation对象加入到NSOperationQueue队列中，一旦这个对象被加入到队列，队列就开始处理这个对象，直到这个对 象的全部操做完成。而后它被队列释放。  下面的例子中，使用一个获取网页，并对其解析程NSXMLDocument，最后将解析获得的NSXMLDocument返回给主线程。        PageLoadOperation.h@interface PageLoadOperation : NSOperation {      NSURL *targetURL;}  @property(retain) NSURL *targetURL;  - (id)initWithURL:(NSURL*)url;@end    PageLoadOperation.m  #import "PageLoadOperation.h"#import "AppDelegate.h"@implementation PageLoadOperation@synthesize targetURL;- (id)initWithURL:(NSURL*)url;{      if (![super init]) return nil;      [self setTargetURL:url];      return self;}- (void)dealloc {      [targetURL release], targetURL = nil;      [super dealloc];  }  - (void)main   {      NSString *webpageString = [[[NSString alloc]      initWithContentsOfURL:[self targetURL]] autorelease];      NSError *error = nil;      NSXMLDocument *document = [[NSXMLDocument alloc]      initWithXMLString:webpageString       options:NSXMLDocumentTidyHTML error:&error];      if (!document) {          NSLog(@"%s Error loading document (%@): %@",           _cmd, [[self targetURL] absoluteString], error);           return;      }      [[AppDelegate shared]      performSelectorOnMainThread:@selector(pageLoaded:)           withObject:document waitUntilDone:YES];      [document release];  }  @end      正 如咱们所看到的那样，这个类至关的简单，在它的init方法中接受一个url并保存起来，当main函数被调用的时候，它使用这个保存的url建立一个字 符串，并将这个字符串传递给NSXMLDocumentinit方法。若是加载的xml数据没有出错，数据会被传递给AppDelegate，它处于主线 程中。到此，这个线程的任务就完成了。在主线程中注销操做队列的时候，会将这个NSOperation对象释放。  AppDelegate.h  @interface AppDelegate : NSObject {      NSOperationQueue *queue;  }+ (id)shared;- (void)pageLoaded:(NSXMLDocument*)document;@endAppDelegate.m        #import "AppDelegate.h"#import "PageLoadOperation.h"@implementation AppDelegate  static AppDelegate *shared;  static NSArray *urlArray;  - (id)init  {      if (shared)      {          [self autorelease];          return shared;      }      if (![super init]) return nil;    NSMutableArray *array = [[NSMutableArray alloc] init];[array addObject:@"http://www.google.com"];[array addObject:@"http://www.apple.com"];[array addObject:@"http://www.yahoo.com"];[array addObject:@"http://www.zarrastudios.com"];[array addObject:@"http://www.macosxhints.com"];urlArray = array;    queue = [[NSOperationQueue alloc] init];shared = self;return self;      }      •    (void)applicationDidFinishLaunching:      (NSNotification *)aNotification  {          for (NSString *urlString in urlArray)           {          NSURL *url =           [NSURL URLWithString:urlString];        PageLoadOperation *plo =           [[PageLoadOperation alloc] initWithURL:url];          [queue addOperation:plo];          [plo release];          }  }  - (void)dealloc  {          [queue release], queue = nil;          [super dealloc];  }  + (id)shared;  {          if (!shared) {              [[AppDelegate alloc] init];          }          return shared;  }  - (void)pageLoaded:(NSXMLDocument*)document;  {          NSLog(@"%s Do something with the XMLDocument: %@",               _cmd, document);  }  @end    NSOperationQueue的并行控制（NSOperationQueue Concurrency）          在 上面这个简单的例子中，咱们很难看出这些操做是并行运行的，然而，若是你你的操做花费的时间远远比这里的要长，你将会发现，队列是同时执行这些操做的。幸 运的是，若是你想要为队列限制同时只能运行几个操做，你可使用NSOperationQueue的 setMaxConcurrentOperationCount:方法。例如，[queue setMaxConcurrentOperationCount:2];