iOS開發筆記（六）網路編程總結

轉載自：http://www.cocoachina.com/bbs/read.php?tid-31300.html 一：確認網路環境3G/WIFI    1. 添加源檔案和framework
    
    開發Web等網路應用程式的時候，需要確認網路環境，串連情況等資訊。如果沒有處理它們，是不會通過Apple的審查的。
    Apple 的 常式 Reachability 中介紹了取得/檢測網路狀態的方法。要在應用程式程式中使用Reachability，首先要完成如下兩部：
    
    1.1. 添加源檔案：
    在你的程式中使用 Reachability 只須將該常式中的 Reachability.h 和 Reachability.m 拷貝到你的工程中。如：

    
    
    1.2.添加framework：
    將SystemConfiguration.framework 添加進工程。如：
    
    
    2. 網路狀態
    
    Reachability.h中定義了三種網路狀態：
    typedef enum {
        NotReachable = 0,            //無串連
        ReachableViaWiFi,            //使用3G/GPRS網路
        ReachableViaWWAN            //使用WiFi網路
    } NetworkStatus;
    
    因此可以這樣檢查網路狀態：

    Reachability *r = [Reachability reachabilityWithHostName:@“www.apple.com”];
    switch ([r currentReachabilityStatus]) {
            case NotReachable:
                    // 沒有網路連接
                    break;
            case ReachableViaWWAN:
                    // 使用3G網路
                    break;
            case ReachableViaWiFi:
                    // 使用WiFi網路
                    break;
    }
    
    3.檢查當前網路環境
    程式啟動時，如果想檢測可用的網路環境，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. 連結狀態的即時通知
    網路連接狀態的即時檢查，通知在網路應用中也是十分必要的。接續狀態發生變化時，需要及時地通知使用者：
    
    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;

    // 更新網路狀態
    - (void)updateStatus {
        self.remoteHostStatus = [[Reachability sharedReachability] remoteHostStatus];
    }

    // 通知網路狀態
    - (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];
        }
    }

    // 程式啟動器，啟動網路監視
    - (void)applicationDidFinishLaunching:(UIApplication *)application {
    
        // 設定網路檢測的網站
        [[Reachability sharedReachability] setHostName:@"www.apple.com"];
        [[Reachability sharedReachability] setNetworkStatusNotificationsEnabled:YES];
        // 設定網路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 {
        // ...
                  
        // 監測網路情況
        [[NSNotificationCenter defaultCenter] addObserver:self
                              selector:@selector(reachabilityChanged:)
                              name: kReachabilityChangedNotification
                              object: nil];
        hostReach = [[Reachability reachabilityWithHostName:@"www.google.com"] retain];
        hostReach startNotifer];
        // ...
    }

二：使用NSConnection下載資料
    
    1.建立NSConnection對象，設定委派物件
    
    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];            //通常在這裡先清空接受資料的緩衝
    }
    
    - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
           /* appends the new data to the received data */
        [self.receivedData appendData:data];        //可能多次收到資料，把新的資料添加在現有資料最後
    }

    - (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檔案

    1. 設定委派物件，開始解析
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];   //或者也可以使用initWithContentsOfURL直接下載檔案，但是有一個原因不這麼做：
    // 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{
        // 元素開始控制代碼
        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
    {
        // 元素終了控制代碼
        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];