iPhone 网络连接检测(Wifi,3G,Edge)，功能有点像Reachability

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　　这个类可以用来检测用户是否连接到internet.  用法非常简单，只有一个方法，返回 YES或NO。
　　一个简单的例子：



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• if ([Connection isConnected]) {  ...  }     
  
• else {  ...  }   
  

　　这个类的头文件：



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• //     
  
• //  Connection.h      
  
• //     
  
• #import <Foundation/Foundation.h>     
  
• #import <SystemConfiguration/SystemConfiguration.h>     
  
• #import <netinet/in.h>     
  
• #import <arpa/inet.h>     
  
• #import <netdb.h>     
  
•    
  
• @interface Connection : NSObject {     
  
•    
  
• }     
  
•    
  
• + (BOOL) isConnected;     
  
•    
  
• @end   
  

　　类的实现文件：



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• //     
  
• //  Connection.m   
  
• //     
  
•    
  
• #import "Connection.h"     
  
•    
  
• @implementation Connection     
  
•    
  
• + (BOOL) isConnected {     
  
•     // Create zero addy     
  
•     struct sockaddr_in zeroAddress;     
  
•     bzero(&zeroAddress, sizeof(zeroAddress));     
  
•     zeroAddress.sin_len = sizeof(zeroAddress);     
  
•     zeroAddress.sin_family = AF_INET;     
  
•     // Recover reachability flags     
  
•     SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);     
  
•     SCNetworkReachabilityFlags flags;     
  
•     BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);     
  
•     CFRelease(defaultRouteReachability);     
  
•     if (!didRetrieveFlags) {     
  
•         NSLog(@"Error. Could not recover network reachability flags");     
  
•         return NO;     
  
•     }     
  
•     BOOL isReachable = flags & kSCNetworkFlagsReachable;     
  
•     BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;     
  
•     BOOL nonWiFi = flags & kSCNetworkReachabilityFlagsTransientConnection;     
  
•     NSURL *testURL = [NSURL URLWithString:@"http://www.google.com/"];     
  
•     NSURLRequest *testRequest = [NSURLRequest requestWithURL:testURL  cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:20.0];     
  
•     NSURLConnection *testConnection = [[[NSURLConnection alloc] initWithRequest:testRequest delegate:self] autorelease];     
  
•     return ((isReachable && !needsConnection) || nonWiFi) ? (testConnection ? YES : NO) : NO;     
  
• }     
  
•    
  
• @end   
  

　　最后别忘了添加必要的frameworks: SystemConfiguration and libz.1.1.3.dylib
　　标题中提到的Reachability也具有检测网络的功能。大家可以参考资料：http://www.raddonline.com/blogs/geek-journal/iphone-sdk-testing-network-reachability/
　　http://blog.iyunv.com/favormm/article/details/5352656