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

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：

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

这个类的头文件：

//   
//  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：

//   
//  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://developer.apple.com/iphone/library/samplecode/Reachability/index.html