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://blog.csdn.net/favormm/article/details/5352656