ios網絡編程

一：確認網絡環境3G/WIFI 
 
    1. 添加源文件和framework 
     
    開發Web等網絡應用程序的時候，須要確認網絡環境，鏈接狀況等信息。若是沒有處理它們，是不會經過Apple的審查的。 
    Apple 的 例程 Reachability 中介紹了取得/檢測網絡狀態的方法。要在應用程序程序中使用Reachability，首先要完成以下兩部： 
     
    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。以下圖： 
 
     
     
    1.2.添加framework： 
    將SystemConfiguration.framework 添加進工程。以下圖： 
     
     
    2. 網絡狀態 
     
    Reachability.h中定義了三種網絡狀態： 
    typedef enum { 
        NotReachable = 0,            //無鏈接 
        ReachableViaWiFi,            //使用3G/GPRS網絡 
        ReachableViaWWAN            //使用WiFi網絡 
    } NetworkStatus; 
     
    所以能夠這樣檢查網絡狀態： 
 
    Reachability *r = [Reachability reachabilityWithHostName:@「 www.apple.com」]; 
    switch ([r currentReachabilityStatus]) { 
            case NotReachable: 
                    // 沒有網絡鏈接 
                    break; 
            case ReachableViaWWAN: 
                    // 使用3G網絡 
                    break; 
            case ReachableViaWiFi: 
                    // 使用WiFi網絡 
                    break; 
    } 
     
    3.檢查當前網絡環境 
    程序啓動時，若是想檢測可用的網絡環境，能夠像這樣 
    // 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. 連接狀態的實時通知 
    網絡鏈接狀態的實時檢查，通知在網絡應用中也是十分必要的。接續狀態發生變化時，須要及時地通知用戶： 
     
    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; 
 
    // 更新網絡狀態 
    - (void)updateStatus { 
        self.remoteHostStatus = [[Reachability sharedReachability] remoteHostStatus]; 
    } 
 
    // 通知網絡狀態 
    - (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]; 
        } 
    } 
 
    // 程序啓動器，啓動網絡監視 
    - (void)applicationDidFinishLaunching:(UIApplication *)application { 
     
        // 設置網絡檢測的站點 
        [[Reachability sharedReachability] setHostName:@"www.apple.com"]; 
        [[Reachability sharedReachability] setNetworkStatusNotificationsEnabled:YES]; 
        // 設置網絡狀態變化時的通知函數 
        [[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 { 
        // ... 
                   
        // 監測網絡狀況 
        [[NSNotificationCenter defaultCenter] addObserver:self 
                              selector:@selector(reachabilityChanged:) 
                              name: kReachabilityChangedNotification 
                              object: nil]; 
        hostReach = [[Reachability reachabilityWithHostName:@"www.google.com"] retain]; 
        hostReach startNotifer]; 
        // ... 
    } 
 
 
二：使用NSConnection下載數據 
     
    1.建立NSConnection對象，設置委託對象 
     
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self urlString]]]; 
    [NSURLConnection connectionWithRequest:request delegate:self]; 
     
    2. NSURLConnection delegate委託方法 
        - (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. 實現委託方法 
    - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { 
        // store data 
        [self.receivedData setLength:0];            //一般在這裏先清空接受數據的緩存 
    } 
     
    - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { 
           /* appends the new data to the received data */ 
        [self.receivedData appendData:data];        //可能屢次收到數據，把新的數據添加在現有數據最後 
    } 
 
    - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error { 
        // 錯誤處理 
    } 
 
    - (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. 設置委託對象，開始解析 
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];   //或者也可使用initWithContentsOfURL直接下載文件，可是有一個緣由不這麼作： 
    // 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. 經常使用的委託方法 
    - (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];

使用NSOperation和NSOperationQueue啓動多線程

在app store中的不少應用程序很是的笨重，他們有好的界面，但操做性不好，好比說當程序從網上或本地載入數據的時候，界面被凍結了，用戶只能等程序徹底載入數據以後才能進行操做。  當 打開一個應用程序時，iphone會產生一個包含main方法的線程，所用程序中的界面都是運行在這個線程之中的（table views, tab bars, alerts…）,有時候咱們會用數據填充這些view，如今問        題是如何有效的載入數據，而且用戶還能自如的操做程序。方法是啓動新的線 程，專門用於數據的下載，而主線程不會由於下載數據被阻塞。  無論使用任何編程語言，在實現多線程時都是一件很麻煩的事情。更糟糕的是，一旦出 錯，這種錯誤一般至關糟糕。然而，幸運的是apple從os x10.5在這方面作了不少的改進，NSThread的引入，使得開發多線程應用程序容易多了。除此以外，它們還引入了兩個全新的 類，NSOperation和NSOperationQueue。  接下來咱們經過一個實例來剖析如何使用這兩個類實現多線程。這裏指示展現這兩個類的基本用法，固然這不是使用他們的惟一辦法。  如 果你熟悉java或者它的別的變種語言的話 ，你會發現NSOperation對象很像java.lang.Runnable接口，就像java.lang.Runnable接口那 樣，NSOperation類也被設計爲可擴展的，並且只有一個須要重寫的方法。它就是－(void)main。使用NSOperation的最簡單的方 式就是把一個NSOperation對象加入到NSOperationQueue隊列中，一旦這個對象被加入到隊列，隊列就開始處理這個對象，直到這個對 象的全部操做完成。而後它被隊列釋放。  下面的例子中，使用一個獲取網頁，並對其解析程NSXMLDocument，最後將解析獲得的NSXMLDocument返回給主線程。        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 如咱們所看到的那樣，這個類至關的簡單，在它的init方法中接受一個url並保存起來，當main函數被調用的時候，它使用這個保存的url建立一個字 符串，並將這個字符串傳遞給NSXMLDocumentinit方法。若是加載的xml數據沒有出錯，數據會被傳遞給AppDelegate，它處於主線 程中。到此，這個線程的任務就完成了。在主線程中註銷操做隊列的時候，會將這個NSOperation對象釋放。  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的並行控制（NSOperationQueue Concurrency）          在 上面這個簡單的例子中，咱們很難看出這些操做是並行運行的，然而，若是你你的操做花費的時間遠遠比這裏的要長，你將會發現，隊列是同時執行這些操做的。幸 運的是，若是你想要爲隊列限制同時只能運行幾個操做，你可使用NSOperationQueue的 setMaxConcurrentOperationCount:方法。例如，[queue setMaxConcurrentOperationCount:2];