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一、确认网络环境3G/WiFi

1). 要在应用程序中使用Reachability，首先要完成以下两步骤：

1.1 添加源文件：将Reachability.h和Reachability.m拷贝到你工程中。

1.2 添加必要框架：将SystemConfiguration.framework添加到工程项目中。 

2). 检查网络状态

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; }

3). 检查当前网络环境

程序启动时，如果想检测可用的网络环境，可以这样：

// 是否WiFi

+ (BOOL) IsEnableWIFI {

    return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable);

}

// 是否3G

+ (BOOL) IsEnable3G {

    return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable);

} 

- (void)viewWillAppear:(BOOL)animated {
   if(([Reachability reachabilityForInternetConnection].currentReachabilityStatus == NotReachable) && ([Reachability reachabilityForLocalWiFi].currentReachabilityStatus == NotReachable)) {
           self.navigationItem.hidesBackButton = YES;         [self.navigationItem setLeftBarButtonItem:nil  animated:NO];    } }

4). 链接状态的实时通知

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。

Reachability 1.5版本

// My.AppDelegate.h #import "Reachability.h" @interface MyAppDelegate : NSObject 
     
       {
       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:NSLocalizedStrng(@"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]; }
     

Reachability 2.0版本

// MyAppDelegate.h @class  Reachability; @interface  MyAppDelegate:NSObject
     
       {
       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]; //..... }
     

详细：http://www.cocoachina.com/bbs/read.php?tid=31300