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由于设计的游戏需要有一些联网请求，但有时候在设备未连接网络的情况下，如果对网络情况不加以判断，则可能造成游戏为了等游戏超时，浪费不必要的时间。
所以在游戏启动时检测一下网络状况是很必要的，而且当玩家的设备连接上网络以后，有一个回调函数也是非常必要的一件事儿，这样可能更方便我们在后台下载数据库等信息。
apple为我们提供了一套范例代码，下面我就来分析一下这段代码。
范例代码地址在：
范例中包含两部分，一部分是appdelegate,一部分是reachability
1 #import2 #import 3 #import 4 #import 5 #import 6 #import 7 8 #import 9 10 #import "Reachability.h" 11 12 #define kShouldPrintReachabilityFlags 1 13 14 static void PrintReachabilityFlags(SCNetworkReachabilityFlags flags, const char* comment) 15 { 16 #if kShouldPrintReachabilityFlags 17 18 NSLog(@"Reachability Flag Status: %c%c %c%c%c%c%c%c%c %s\n", 19 (flags & kSCNetworkReachabilityFlagsIsWWAN) ? 'W' : '-',//当前网络为蜂窝网络，即3G或者GPRS 20 (flags & kSCNetworkReachabilityFlagsReachable) ? 'R' : '-',//网络请求地址可达 21 22 (flags & kSCNetworkReachabilityFlagsTransientConnection) ? 't' : '-', 23 (flags & kSCNetworkReachabilityFlagsConnectionRequired) ? 'c' : '-', 24 (flags & kSCNetworkReachabilityFlagsConnectionOnTraffic) ? 'C' : '-', 25 (flags & kSCNetworkReachabilityFlagsInterventionRequired) ? 'i' : '-', 26 (flags & kSCNetworkReachabilityFlagsConnectionOnDemand) ? 'D' : '-', 27 (flags & kSCNetworkReachabilityFlagsIsLocalAddress) ? 'l' : '-',//该值为一个本地地址 28 (flags & kSCNetworkReachabilityFlagsIsDirect) ? 'd' : '-', 29 comment 30 ); 31 #endif 32 } 33 34 35 @implementation Reachability 36 static void ReachabilityCallback(SCNetworkReachabilityRef target, SCNetworkReachabilityFlags flags, void* info) 37 { 38 #pragma unused (target, flags) 39 NSCAssert(info != NULL, @"info was NULL in ReachabilityCallback"); 40 NSCAssert([(NSObject*) info isKindOfClass: [Reachability class]], @"info was wrong class in ReachabilityCallback"); 41 42 //We're on the main RunLoop, so an NSAutoreleasePool is not necessary, but is added defensively 43 // in case someon uses the Reachablity object in a different thread. 44 NSAutoreleasePool* myPool = [[NSAutoreleasePool alloc] init]; 45 46 Reachability* noteObject = (Reachability*) info; 47 // Post a notification to notify the client that the network reachability changed. 48 [[NSNotificationCenter defaultCenter] postNotificationName: kReachabilityChangedNotification object: noteObject]; 49 50 [myPool release]; 51 } 52 53 54 55 //启动探测网络 56 - (BOOL) startNotifier 57 { 58 BOOL retVal = NO; 59 SCNetworkReachabilityContext context = { 0, self, NULL, NULL, NULL}; 60 //SCNetworkReachabilitySetCallback函数为指定一个target（此处为reachabilityRef，即www.apple.com,在reachabilityWithHostName里设置的） 61 //当设备对于这个target链接状态发生改变时(比如断开链接，或者重新连上)，则回调reachabilityCallback函数， 62 if(SCNetworkReachabilitySetCallback(reachabilityRef, ReachabilityCallback, &context)) 63 { 64 //指定一个runloop给指定的target 65 if(SCNetworkReachabilityScheduleWithRunLoop(reachabilityRef, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode)) 66 { 67 retVal = YES; 68 } 69 } 70 return retVal; 71 } 72 //停止网络探测 73 - (void) stopNotifier 74 { 75 if(reachabilityRef!= NULL) 76 { 77 SCNetworkReachabilityUnscheduleFromRunLoop(reachabilityRef, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode); 78 } 79 } 80 81 - (void) dealloc 82 { 83 [self stopNotifier]; 84 if(reachabilityRef!= NULL) 85 { 86 CFRelease(reachabilityRef); 87 } 88 [super dealloc]; 89 } 90 //通过域名设定一个目标地址比如www.apple.com 91 + (Reachability*) reachabilityWithHostName: (NSString*) hostName; 92 { 93 Reachability* retVal = NULL; 94 SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(NULL, [hostName UTF8String]); 95 if(reachability!= NULL) 96 { 97 retVal= [[[self alloc] init] autorelease]; 98 if(retVal!= NULL) 99 {100 retVal->reachabilityRef = reachability;101 retVal->localWiFiRef = NO;102 }103 }104 return retVal;105 }106 //通过ip地址设定一个目标的地址，可以加端口号，貌似我实验的不太成功107 + (Reachability*) reachabilityWithAddress: (const struct sockaddr_in*) hostAddress;108 {109 SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, (const struct sockaddr*)hostAddress);110 Reachability* retVal = NULL;111 if(reachability!= NULL)112 {113 retVal= [[[self alloc] init] autorelease];114 if(retVal!= NULL)115 {116 retVal->reachabilityRef = reachability;117 retVal->localWiFiRef = NO;118 }119 }120 return retVal;121 }122 //检测当前网络能否连上internet123 + (Reachability*) reachabilityForInternetConnection;124 {125 struct sockaddr_in zeroAddress;126 bzero(&zeroAddress, sizeof(zeroAddress));127 zeroAddress.sin_len = sizeof(zeroAddress);128 zeroAddress.sin_family = AF_INET;129 return [self reachabilityWithAddress: &zeroAddress];130 }131 //检测当前网络是否能够连上本地wifi132 + (Reachability*) reachabilityForLocalWiFi;133 {134 struct sockaddr_in localWifiAddress;135 bzero(&localWifiAddress, sizeof(localWifiAddress));136 localWifiAddress.sin_len = sizeof(localWifiAddress);137 localWifiAddress.sin_family = AF_INET;138 // IN_LINKLOCALNETNUM is defined in as 169.254.0.0139 localWifiAddress.sin_addr.s_addr = htonl(IN_LINKLOCALNETNUM);140 Reachability* retVal = [self reachabilityWithAddress: &localWifiAddress];141 if(retVal!= NULL)142 {143 retVal->localWiFiRef = YES;144 }145 return retVal;146 }147 148 #pragma mark Network Flag Handling149 150 - (NetworkStatus) localWiFiStatusForFlags: (SCNetworkReachabilityFlags) flags151 {152 PrintReachabilityFlags(flags, "localWiFiStatusForFlags");153 154 BOOL retVal = NotReachable;155 if((flags & kSCNetworkReachabilityFlagsReachable) && (flags & kSCNetworkReachabilityFlagsIsDirect))156 {157 retVal = ReachableViaWiFi; 158 }159 return retVal;160 }161 //通过flags返回当前网络状态162 - (NetworkStatus) networkStatusForFlags: (SCNetworkReachabilityFlags) flags163 {164 PrintReachabilityFlags(flags, "networkStatusForFlags");165 if ((flags & kSCNetworkReachabilityFlagsReachable) == 0)166 {167 // if target host is not reachable168 return NotReachable;169 }170 171 BOOL retVal = NotReachable;172 173 if ((flags & kSCNetworkReachabilityFlagsConnectionRequired) == 0)174 {175 // if target host is reachable and no connection is required176 // then we'll assume (for now) that your on Wi-Fi177 retVal = ReachableViaWiFi;178 }179 180 181 if ((((flags & kSCNetworkReachabilityFlagsConnectionOnDemand ) != 0) ||182 (flags & kSCNetworkReachabilityFlagsConnectionOnTraffic) != 0))183 {184 // ... and the connection is on-demand (or on-traffic) if the185 // calling application is using the CFSocketStream or higher APIs186 187 if ((flags & kSCNetworkReachabilityFlagsInterventionRequired) == 0)188 {189 // ... and no [user] intervention is needed190 retVal = ReachableViaWiFi;191 }192 }193 194 if ((flags & kSCNetworkReachabilityFlagsIsWWAN) == kSCNetworkReachabilityFlagsIsWWAN)195 {196 // ... but WWAN connections are OK if the calling application197 // is using the CFNetwork (CFSocketStream?) APIs.198 retVal = ReachableViaWWAN;199 }200 return retVal;201 }202 203 - (BOOL) connectionRequired;204 {205 NSAssert(reachabilityRef != NULL, @"connectionRequired called with NULL reachabilityRef");206 SCNetworkReachabilityFlags flags;207 if (SCNetworkReachabilityGetFlags(reachabilityRef, &flags))208 {209 return (flags & kSCNetworkReachabilityFlagsConnectionRequired);210 }211 return NO;212 }213 //获得当前网络状态214 - (NetworkStatus) currentReachabilityStatus215 {216 NSAssert(reachabilityRef != NULL, @"currentNetworkStatus called with NULL reachabilityRef");217 NetworkStatus retVal = NotReachable;218 SCNetworkReachabilityFlags flags;219 if (SCNetworkReachabilityGetFlags(reachabilityRef, &flags))220 {221 if(localWiFiRef)222 {223 retVal = [self localWiFiStatusForFlags: flags];224 }225 else226 {227 retVal = [self networkStatusForFlags: flags];228 }229 }230 return retVal;231 }232 @end
以上的部分为具体实现的部分，下面我们再来看在appdelegate里面调用的部分
- (void) applicationDidFinishLaunching: (UIApplication* )application { #pragma unused(application) contentView.backgroundColor = [UIColor groupTableViewBackgroundColor]; summaryLabel.hidden = YES; //这句是设定一个回调函数reachability，当网络条件发生变化时则去调用reachabilityChanged [[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(reachabilityChanged:) name: kReachabilityChangedNotification object: nil]; //Change the host name here to change the server your monitoring remoteHostLabel.text = [NSString stringWithFormat: @"Remote Host: %@", @"www.apple.com"]; //设定target地址，这里是www.apple.com hostReach = [[Reachability reachabilityWithHostName: @"www.apple.com"] retain]; //启动网络条件检测 [hostReach startNotifier]; //更新UI的网络状态显示 [self updateInterfaceWithReachability: hostReach]; //探测是否能连上internet网 internetReach = [[Reachability reachabilityForInternetConnection] retain]; [internetReach startNotifier]; [self updateInterfaceWithReachability: internetReach]; //探测wifi是否开启 wifiReach = [[Reachability reachabilityForLocalWiFi] retain]; [wifiReach startNotifier]; [self updateInterfaceWithReachability: wifiReach]; [window makeKeyAndVisible]; }//如需要查看网络状态，如下调用即可NetworkStatus netStatus = [curReach currentReachabilityStatus];netStatus有ReachableViaWWAN（蜂窝网络3G之类的）,ReachableViaWiFi（wifi连接）,NotReachable(无法连接)