前言

在網絡應用中，需要對用戶設備的網絡狀態進行實時監控，有兩個目的：

（1）讓用戶了解自己的網絡狀態，防止一些誤會（比如怪應用無能）

（2）根據用戶的網絡狀態進行智能處理，節省用戶流量，提高用戶體驗

　　WIFI\3G網絡：自動下載高清圖片

　　低速網絡：只下載縮略圖

　　沒有網絡：只顯示離線的緩存數據

最近在工作中遇到一個功能就是根據用戶當前的網絡狀，用戶未聯網需要提示一下，如果是Wifi可以推薦一些圖片新聞，如果是3G模式設置為無圖的模式，獲取網絡狀態比較簡單，畢竟中國現在的流量還是一個比較貴的狀態，哪天用戶發現App消耗流量過多說不定就干掉了App 。 不過蘋果的 Reachability 都解決了以上問題，使用起來也比較方便，所以就總結以下，具體的稍微簡單分析下，下面話不多說，來一起看看詳細的介紹：

示例代碼

Reachability.h頭文件代碼:

#import <Foundation/Foundation.h> 
#import <SystemConfiguration/SystemConfiguration.h> 
#import <netinet/in.h> 
 
//http://www.cnblogs.com/xiaofeixiang 
typedef enum : NSInteger { 
 NotReachable = 0, 
 ReachableViaWiFi, 
 ReachableViaWWAN 
} NetworkStatus; 
 
 
extern NSString *kReachabilityChangedNotification; 
 
 
@interface Reachability : NSObject 
 
/*! 
 * Use to check the reachability of a given host name. 
 */ 
+ (instancetype)reachabilityWithHostName:(NSString *)hostName; 
 
/*! 
 * Use to check the reachability of a given IP address. 
 */ 
+ (instancetype)reachabilityWithAddress:(const struct sockaddr_in *)hostAddress; 
 
/*! 
 * Checks whether the default route is available. Should be used by applications that do not connect to a particular host. 
 */ 
+ (instancetype)reachabilityForInternetConnection; 
 
/*! 
 * Checks whether a local WiFi connection is available. 
 */ 
+ (instancetype)reachabilityForLocalWiFi; 
 
/*! 
 * Start listening for reachability notifications on the current run loop. 
 */ 
- (BOOL)startNotifier; 
- (void)stopNotifier; 
 
- (NetworkStatus)currentReachabilityStatus; 
 
/*! 
 * WWAN may be available, but not active until a connection has been established. WiFi may require a connection for VPN on Demand. 
 */ 
- (BOOL)connectionRequired; 
 
@end

Reachability.m文件:

#import <arpa/inet.h> 
#import <ifaddrs.h> 
#import <netdb.h> 
#import <sys/socket.h> 
#import <CoreFoundation/CoreFoundation.h> 
#import "Reachability.h" 
NSString *kReachabilityChangedNotification = @"kNetworkReachabilityChangedNotification"; 
#pragma mark - Supporting functions 
#define kShouldPrintReachabilityFlags 1 
static void PrintReachabilityFlags(SCNetworkReachabilityFlags flags, const char* comment) 
{ 
#if kShouldPrintReachabilityFlags 
 NSLog(@"Reachability Flag Status: %c%c %c%c%c%c%c%c%c %s\n", 
  //當前網絡2G/3G/4G蜂窩網絡 
  (flags & kSCNetworkReachabilityFlagsIsWWAN)    ? 'W' : '-', 
  //網絡是否可達 
  (flags & kSCNetworkReachabilityFlagsReachable)   ? 'R' : '-', 
  (flags & kSCNetworkReachabilityFlagsTransientConnection) ? 't' : '-', 
  (flags & kSCNetworkReachabilityFlagsConnectionRequired) ? 'c' : '-', 
  (flags & kSCNetworkReachabilityFlagsConnectionOnTraffic) ? 'C' : '-', 
  (flags & kSCNetworkReachabilityFlagsInterventionRequired) ? 'i' : '-', 
  (flags & kSCNetworkReachabilityFlagsConnectionOnDemand) ? 'D' : '-', 
  (flags & kSCNetworkReachabilityFlagsIsLocalAddress)  ? 'l' : '-', 
  (flags & kSCNetworkReachabilityFlagsIsDirect)   ? 'd' : '-', 
  comment 
  ); 
#endif 
} 
static void ReachabilityCallback(SCNetworkReachabilityRef target, SCNetworkReachabilityFlags flags, void* info) 
{ 
#pragma unused (target, flags) 
 NSCAssert(info != NULL, @"info was NULL in ReachabilityCallback"); 
 NSCAssert([(__bridge NSObject*) info isKindOfClass: [Reachability class]], @"info was wrong class in ReachabilityCallback"); 
 //http://www.cnblogs.com/xiaofeixiang 
 Reachability* noteObject = (__bridge Reachability *)info; 
 // Post a notification to notify the client that the network reachability changed. 
 [[NSNotificationCenter defaultCenter] postNotificationName: kReachabilityChangedNotification object: noteObject]; 
} 
#pragma mark - Reachability implementation 
@implementation Reachability 
{ 
 BOOL _alwaysReturnLocalWiFiStatus; //default is NO 
 SCNetworkReachabilityRef _reachabilityRef; 
} 
//通過域名進行實例化 博客園-Fly_Elephant 
+ (instancetype)reachabilityWithHostName:(NSString *)hostName 
{ 
 Reachability* returnValue = NULL; 
 SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(NULL, [hostName UTF8String]); 
 if (reachability != NULL) 
 { 
 returnValue= [[self alloc] init]; 
 if (returnValue != NULL) 
 { 
  returnValue->_reachabilityRef = reachability; 
  returnValue->_alwaysReturnLocalWiFiStatus = NO; 
 } 
 } 
 return returnValue; 
} 
//通過ip地址實例化Reachability 
+ (instancetype)reachabilityWithAddress:(const struct sockaddr_in *)hostAddress 
{ 
 SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, (const struct sockaddr *)hostAddress); 
 Reachability* returnValue = NULL; 
 if (reachability != NULL) 
 { 
 returnValue = [[self alloc] init]; 
 if (returnValue != NULL) 
 { 
  returnValue->_reachabilityRef = reachability; 
  returnValue->_alwaysReturnLocalWiFiStatus = NO; 
 } 
 } 
 return returnValue; 
} 
//檢測是否能夠直接連上互聯網 
+ (instancetype)reachabilityForInternetConnection 
{ 
 struct sockaddr_in zeroAddress; 
 bzero(&zeroAddress, sizeof(zeroAddress)); 
 zeroAddress.sin_len = sizeof(zeroAddress); 
 zeroAddress.sin_family = AF_INET; 
 return [self reachabilityWithAddress:&zeroAddress]; 
} 
//檢測當前網絡是否能夠聯上wifi 
+ (instancetype)reachabilityForLocalWiFi 
{ 
 struct sockaddr_in localWifiAddress; 
 bzero(&localWifiAddress, sizeof(localWifiAddress)); 
 localWifiAddress.sin_len = sizeof(localWifiAddress); 
 localWifiAddress.sin_family = AF_INET; 
 // IN_LINKLOCALNETNUM is defined in <netinet/in.h> as 169.254.0.0. 
 localWifiAddress.sin_addr.s_addr = htonl(IN_LINKLOCALNETNUM); 
 Reachability* returnValue = [self reachabilityWithAddress: &localWifiAddress]; 
 if (returnValue != NULL) 
 { 
 returnValue->_alwaysReturnLocalWiFiStatus = YES; 
 } 
 return returnValue; 
} 
#pragma mark - Start and stop notifier 
- (BOOL)startNotifier 
{ 
 BOOL returnValue = NO; 
 SCNetworkReachabilityContext context = {0, (__bridge voidvoid *)(self), NULL, NULL, NULL}; 
 //SCNetworkReachabilitySetCallback函數為指定一個target 
 //當設備對於這個target鏈接狀態發生改變時(比如斷開鏈接，或者重新連上)，則回調reachabilityCallback函數， 
 if (SCNetworkReachabilitySetCallback(_reachabilityRef, ReachabilityCallback, &context)) 
 { 
 if (SCNetworkReachabilityScheduleWithRunLoop(_reachabilityRef, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode)) 
 { 
  returnValue = YES; 
 } 
 } 
 return returnValue; 
} 
- (void)stopNotifier 
{ 
 if (_reachabilityRef != NULL) 
 { 
 SCNetworkReachabilityUnscheduleFromRunLoop(_reachabilityRef, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode); 
 } 
} 
- (void)dealloc 
{ 
 [self stopNotifier]; 
 if (_reachabilityRef != NULL) 
 { 
 CFRelease(_reachabilityRef); 
 } 
} 
#pragma mark - Network Flag Handling 
- (NetworkStatus)localWiFiStatusForFlags:(SCNetworkReachabilityFlags)flags 
{ 
 PrintReachabilityFlags(flags, "localWiFiStatusForFlags"); 
 NetworkStatus returnValue = NotReachable; 
 if ((flags & kSCNetworkReachabilityFlagsReachable) && (flags & kSCNetworkReachabilityFlagsIsDirect)) 
 { 
 returnValue = ReachableViaWiFi; 
 } 
 return returnValue; 
} 
- (NetworkStatus)networkStatusForFlags:(SCNetworkReachabilityFlags)flags 
{ 
 PrintReachabilityFlags(flags, "networkStatusForFlags"); 
 if ((flags & kSCNetworkReachabilityFlagsReachable) == 0) 
 { 
 // The target host is not reachable. 
 return NotReachable; 
 } 
 NetworkStatus returnValue = NotReachable; 
 if ((flags & kSCNetworkReachabilityFlagsConnectionRequired) == 0) 
 { 
 /* 
  If the target host is reachable and no connection is required then we'll assume (for now) that you're on Wi-Fi... 
  */ 
 returnValue = ReachableViaWiFi; 
 } 
 if ((((flags & kSCNetworkReachabilityFlagsConnectionOnDemand ) != 0) || 
 (flags & kSCNetworkReachabilityFlagsConnectionOnTraffic) != 0)) 
 { 
 /* 
  ... and the connection is on-demand (or on-traffic) if the calling application is using the CFSocketStream or higher APIs... 
  */ 
 if ((flags & kSCNetworkReachabilityFlagsInterventionRequired) == 0) 
 { 
  /* 
  ... and no [user] intervention is needed... 
  */ 
  returnValue = ReachableViaWiFi; 
 } 
 } 
 if ((flags & kSCNetworkReachabilityFlagsIsWWAN) == kSCNetworkReachabilityFlagsIsWWAN) 
 { 
 /* 
  ... but WWAN connections are OK if the calling application is using the CFNetwork APIs. 
  */ 
 returnValue = ReachableViaWWAN; 
 } 
 return returnValue; 
} 
- (BOOL)connectionRequired 
{ 
 NSAssert(_reachabilityRef != NULL, @"connectionRequired called with NULL reachabilityRef"); 
 SCNetworkReachabilityFlags flags; 
 if (SCNetworkReachabilityGetFlags(_reachabilityRef, &flags)) 
 { 
 return (flags & kSCNetworkReachabilityFlagsConnectionRequired); 
 } 
 return NO; 
} 
//獲取當前網絡狀態 
- (NetworkStatus)currentReachabilityStatus 
{ 
 NSAssert(_reachabilityRef != NULL, @"currentNetworkStatus called with NULL SCNetworkReachabilityRef"); 
 NetworkStatus returnValue = NotReachable; 
 SCNetworkReachabilityFlags flags; 
 if (SCNetworkReachabilityGetFlags(_reachabilityRef, &flags)) 
 { 
 if (_alwaysReturnLocalWiFiStatus) 
 { 
  returnValue = [self localWiFiStatusForFlags:flags]; 
 } 
 else 
 { 
  returnValue = [self networkStatusForFlags:flags]; 
 } 
 } 
 return returnValue; 
} 
@end

AppDelegate中的實現:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { 
 //添加一個系統通知 
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:kReachabilityChangedNotification object:nil]; 
 //初始化 
 self.internetReachability=[Reachability reachabilityForInternetConnection]; 
 //通知添加到Run Loop 
 [self.internetReachability startNotifier]; 
 [self updateInterfaceWithReachability:_internetReachability]; 
 return YES; 
} 

回調函數:

(void) reachabilityChanged:(NSNotification *)note 
{ 
 Reachability* curReach = [note object]; 
 NSParameterAssert([curReach isKindOfClass:[Reachability class]]); 
 [self updateInterfaceWithReachability:curReach]; 
} 
- (void)updateInterfaceWithReachability:(Reachability *)reachability 
{ 
 NetworkStatus netStatus = [reachability currentReachabilityStatus]; 
 switch (netStatus) { 
 case NotReachable: 
  NSLog(@"====當前網絡狀態不可達=======http://www.cnblogs.com/xiaofeixiang"); 
  break; 
 case ReachableViaWiFi: 
  NSLog(@"====當前網絡狀態為Wifi=======博客園-Fly_Elephant"); 
  break; 
 case ReachableViaWWAN: 
  NSLog(@"====當前網絡狀態為3G=======keso"); 
  break; 
 } 
} 

總結

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