请从Apple网站下载示例：点此下载
然后将Reachability.h 和 Reachability.m 加到自己的项目中，并引用 SystemConfiguration.framework，就可以使用了。
Reachability 中定义了3种网络状态：
<span style="font-size:14px;">// the network state of the device for Reachability 1.5.
typedef enum {
NotReachable = 0, //无连接
ReachableViaCarrierDataNetwork, //使用3G/GPRS网络
ReachableViaWiFiNetwork //使用WiFi网络
} NetworkStatus;
// the network state of the device for Reachability 2.0.
typedef enum { NotReachable = 0, //无连接
ReachableViaWiFi, //使用3G/GPRS网络
ReachableViaWWAN //使用WiFi网络
} NetworkStatus;</span>
比如检测某一特定站点的接续状况，可以使用下面的代码：
<span style="font-size:14px;">Reachability *r = [Reachability reachabilityWithHostName:@“www.apple.com”];
switch ([r currentReachabilityStatus]) {
case NotReachable: // 没有网络连接
break;
case ReachableViaWWAN: // 使用3G网络
break;
case ReachableViaWiFi: // 使用WiFi网络
break;
}</span>
检测当前网络环境：
<span style="font-size:14px;">// 是否wifi
+ (BOOL) IsEnableWIFI {
return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable);
}
// 是否3G
+ (BOOL) IsEnable3G {
return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable);
}</span>
连接状态实时通知
网络连接状态的实时检查，通知在网络应用中也是十分必要的。接续状态发生变化时，需要及时地通知用户。由于Reachability1.5版与2.0版有一些变化，这里分开来说明使用方法。
Reachability 1.5
<span style="font-size:14px;">// 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;
// 更新网络状态
- (void)updateStatus {
self.remoteHostStatus = [[Reachability sharedReachability] remoteHostStatus];
}
// 通知网络状态
- (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];
}
}
// 程序启动器，启动网络监视
- (void)applicationDidFinishLaunching:(UIApplication *)application {
// 设置网络检测的站点
[[Reachability sharedReachability] setHostName:@"www.apple.com"];
[[Reachability sharedReachability] setNetworkStatusNotificationsEnabled:YES];
// 设置网络状态变化时的通知函数
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:@"kNetworkReachabilityChangedNotification" object:nil];
[self updateStatus];
}
- (void)dealloc {
// 删除通知对象
[[NSNotificationCenter defaultCenter] removeObserver:self];
[window release];
[super dealloc];
}</span>
Reachability 2.0
<span style="font-size:14px;">// 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 {
// ...
// 监测网络情况
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name: kReachabilityChangedNotification object: nil];
hostReach = [[Reachability reachabilityWithHostName:@"www.google.com"] retain];
[hostReach startNotifer];
// ...
}</span>
