关于在iOS设备上探测WIFI，3G，GPRS使用情况的细节

转自：http://blog.csdn.net/devfun/article/details/7365774

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：https://developer.apple.com/library/ios/#samplecode/Reachability/Listings/Classes_ReachabilityAppDelegate_m.html#//apple_ref/doc/uid/DTS40007324-Classes_ReachabilityAppDelegate_m-DontLinkElementID_4

范例中包含两部分，一部分是appdelegate,一部分是reachability

#import <sys/socket.h>
#import <netinet/in.h>
#import <netinet6/in6.h>
#import <arpa/inet.h>
#import <ifaddrs.h>
#import <netdb.h>

#import <CoreFoundation/CoreFoundation.h>

#import "Reachability.h"

#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",
(flags & kSCNetworkReachabilityFlagsIsWWAN)               ? 'W' : '-',//当前网络为蜂窝网络，即3G或者GPRS
(flags & kSCNetworkReachabilityFlagsReachable)            ? 'R' : '-',//网络请求地址可达

(flags & kSCNetworkReachabilityFlagsTransientConnection)  ? 't' : '-',
(flags & kSCNetworkReachabilityFlagsConnectionRequired)   ? 'c' : '-',
(flags & kSCNetworkReachabilityFlagsConnectionOnTraffic)  ? 'C' : '-',
(flags & kSCNetworkReachabilityFlagsInterventionRequired) ? 'i' : '-',
(flags & kSCNetworkReachabilityFlagsConnectionOnDemand)   ? 'D' : '-',
(flags & kSCNetworkReachabilityFlagsIsLocalAddress)       ? 'l' : '-',//该值为一个本地地址
(flags & kSCNetworkReachabilityFlagsIsDirect)             ? 'd' : '-',
comment
);
#endif
}

@implementation Reachability
static void ReachabilityCallback(SCNetworkReachabilityRef target, SCNetworkReachabilityFlags flags, void* info)
{
#pragma unused (target, flags)
NSCAssert(info != NULL, @"info was NULL in ReachabilityCallback");
NSCAssert([(NSObject*) info isKindOfClass: [Reachability class]], @"info was wrong class in ReachabilityCallback");

//We're on the main RunLoop, so an NSAutoreleasePool is not necessary, but is added defensively
// in case someon uses the Reachablity object in a different thread.
NSAutoreleasePool* myPool = [[NSAutoreleasePool alloc] init];

Reachability* noteObject = (Reachability*) info;
// Post a notification to notify the client that the network reachability changed.
[[NSNotificationCenter defaultCenter] postNotificationName: kReachabilityChangedNotification object: noteObject];

[myPool release];
}

//启动探测网络
- (BOOL) startNotifier
{
BOOL retVal = NO;
SCNetworkReachabilityContext    context = {0, self, NULL, NULL, NULL};
//SCNetworkReachabilitySetCallback函数为指定一个target（此处为reachabilityRef，即www.apple.com,在reachabilityWithHostName里设置的）
//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，
if(SCNetworkReachabilitySetCallback(reachabilityRef, ReachabilityCallback, &context))
{
//指定一个runloop给指定的target
if(SCNetworkReachabilityScheduleWithRunLoop(reachabilityRef, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode))
{
retVal = YES;
}
}
return retVal;
}
//停止网络探测
- (void) stopNotifier
{
if(reachabilityRef!= NULL)
{
SCNetworkReachabilityUnscheduleFromRunLoop(reachabilityRef, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode);
}
}

- (void) dealloc
{
[self stopNotifier];
if(reachabilityRef!= NULL)
{
CFRelease(reachabilityRef);
}
[super dealloc];
}
//通过域名设定一个目标地址比如www.apple.com
+ (Reachability*) reachabilityWithHostName: (NSString*) hostName;
{
Reachability* retVal = NULL;
SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(NULL, [hostName UTF8String]);
if(reachability!= NULL)
{
retVal= [[[self alloc] init] autorelease];
if(retVal!= NULL)
{
retVal->reachabilityRef = reachability;
retVal->localWiFiRef = NO;
}
}
return retVal;
}
//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
+ (Reachability*) reachabilityWithAddress: (const struct sockaddr_in*) hostAddress;
{
SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, (const struct sockaddr*)hostAddress);
Reachability* retVal = NULL;
if(reachability!= NULL)
{
retVal= [[[self alloc] init] autorelease];
if(retVal!= NULL)
{
retVal->reachabilityRef = reachability;
retVal->localWiFiRef = NO;
}
}
return retVal;
}
//检测当前网络能否连上internet
+ (Reachability*) reachabilityForInternetConnection;
{
struct sockaddr_in zeroAddress;
bzero(&zeroAddress, sizeof(zeroAddress));
zeroAddress.sin_len = sizeof(zeroAddress);
zeroAddress.sin_family = AF_INET;
return [self reachabilityWithAddress: &zeroAddress];
}
//检测当前网络是否能够连上本地wifi
+ (Reachability*) 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* retVal = [self reachabilityWithAddress: &localWifiAddress];
if(retVal!= NULL)
{
retVal->localWiFiRef = YES;
}
return retVal;
}

#pragma mark Network Flag Handling

- (NetworkStatus) localWiFiStatusForFlags: (SCNetworkReachabilityFlags) flags
{
PrintReachabilityFlags(flags, "localWiFiStatusForFlags");

BOOL retVal = NotReachable;
if((flags & kSCNetworkReachabilityFlagsReachable) && (flags & kSCNetworkReachabilityFlagsIsDirect))
{
retVal = ReachableViaWiFi;
}
return retVal;
}
//通过flags返回当前网络状态
- (NetworkStatus) networkStatusForFlags: (SCNetworkReachabilityFlags) flags
{
PrintReachabilityFlags(flags, "networkStatusForFlags");
if ((flags & kSCNetworkReachabilityFlagsReachable) == 0)
{
// if target host is not reachable
return NotReachable;
}

BOOL retVal = NotReachable;

if ((flags & kSCNetworkReachabilityFlagsConnectionRequired) == 0)
{
// if target host is reachable and no connection is required
//  then we'll assume (for now) that your on Wi-Fi
retVal = 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
retVal = ReachableViaWiFi;
}
}

if ((flags & kSCNetworkReachabilityFlagsIsWWAN) == kSCNetworkReachabilityFlagsIsWWAN)
{
// ... but WWAN connections are OK if the calling application
//     is using the CFNetwork (CFSocketStream?) APIs.
retVal = ReachableViaWWAN;
}
return retVal;
}

- (BOOL) connectionRequired;
{
NSAssert(reachabilityRef != NULL, @"connectionRequired called with NULL reachabilityRef");
SCNetworkReachabilityFlags flags;
if (SCNetworkReachabilityGetFlags(reachabilityRef, &flags))
{
return (flags & kSCNetworkReachabilityFlagsConnectionRequired);
}
return NO;
}
//获得当前网络状态
- (NetworkStatus) currentReachabilityStatus
{
NSAssert(reachabilityRef != NULL, @"currentNetworkStatus called with NULL reachabilityRef");
NetworkStatus retVal = NotReachable;
SCNetworkReachabilityFlags flags;
if (SCNetworkReachabilityGetFlags(reachabilityRef, &flags))
{
if(localWiFiRef)
{
retVal = [self localWiFiStatusForFlags: flags];
}
else
{
retVal = [self networkStatusForFlags: flags];
}
}
return retVal;
}
@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)