获得网络状态和实时监控网络状态改变

Apple 的例程 Reachability 中介绍了取得/检测网络状态的方法。在你的程序中使用 Reachability 只须将该例程中的 Reachability.h 和 Reachability.m 拷贝到你的工程中。

Reachability 中定义了3种网络状态：

NotReachable

无连接
ReachableViaCarrierDataNetwork （ReachableViaWWAN）

使用3G/GPRS网络
ReachableViaWiFiNetwork (ReachableViaWiFi)

使用WiFi网络

检测莫个特定站点的连接状况

    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;
    }

检测当前网络环境

    // 是否wifi
    + (BOOL) IsEnableWIFI 
    {
        return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable);
    }
    
    // 是否3G
    + (BOOL) IsEnable3G 
    {
        return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable);
    }

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

// 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];
}

Reachability 2.0

// 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];
    // ...
}