iphone开发使用Reachability判断网络状态

在使用Reachability判断网络状态时，我们可以下载苹果官网的Reachability.zip文件，解压之后有一个不错的实例供我们参考。

1、下载 http://developer.apple.com/library/ios/samplecode/Reachability/Reachability.zip

复制里面的 Reachability.h 和 Reachability.m 到项目中

2、添加 framework：

将 SystemConfiguration.framework 添加进工程。

在这里描述一下示例中的代码

下面的代码设置UITextField的值以及显示的图片。

- (void) configureTextField: (UITextField*) textField imageView: (UIImageView*) imageView reachability: (Reachability*) curReach
{
    NetworkStatus netStatus = [curReach currentReachabilityStatus];
    BOOL connectionRequired= [curReach connectionRequired];
    NSString* statusString= @"";
    switch (netStatus)
    {
        case NotReachable:
        {
            statusString = @"Access Not Available";
            imageView.image = [UIImage imageNamed: @"stop-32.png"] ;
            //Minor interface detail- connectionRequired may return yes, even when the host is unreachable.  We cover that up here...
            connectionRequired= NO;  
            break;
        }
            
        case ReachableViaWWAN:
        {
            statusString = @"Reachable WWAN";
            imageView.image = [UIImage imageNamed: @"WWAN5.png"];
            break;
        }
        case ReachableViaWiFi:
        {
             statusString= @"Reachable WiFi";
            imageView.image = [UIImage imageNamed: @"Airport.png"];
            break;
      }
    }
    if(connectionRequired)
    {
        statusString= [NSString stringWithFormat: @"%@, Connection Required", statusString];
    }
    textField.text= statusString;
}

在这里可以更UITextField的显示，以及图片的显示

- (void) updateInterfaceWithReachability: (Reachability*) curReach
{
    if(curReach == hostReach)
	{
		[self configureTextField: remoteHostStatusField imageView: remoteHostIcon reachability: curReach];
        NetworkStatus netStatus = [curReach currentReachabilityStatus];
        BOOL connectionRequired= [curReach connectionRequired];

        summaryLabel.hidden = (netStatus != ReachableViaWWAN);
        NSString* baseLabel=  @"";
        if(connectionRequired)
        {
            baseLabel=  @"Cellular data network is available.\n  Internet traffic will be routed through it after a connection is established.";
        }
        else
        {
            baseLabel=  @"Cellular data network is active.\n  Internet traffic will be routed through it.";
        }
        summaryLabel.text= baseLabel;
    }
	if(curReach == internetReach)
	{	
		[self configureTextField: internetConnectionStatusField imageView: internetConnectionIcon reachability: curReach];
	}
	if(curReach == wifiReach)
	{	
		[self configureTextField: localWiFiConnectionStatusField imageView: localWiFiConnectionIcon reachability: curReach];
	}
	
}

当网络状态发生变化时会更改状态，以及UITextField，图片的显示。

- (void) reachabilityChanged: (NSNotification* )note
{
	Reachability* curReach = [note object];
	NSParameterAssert([curReach isKindOfClass: [Reachability class]]);
	[self updateInterfaceWithReachability: curReach];
}

如果我们要实时检测当前的网络状态就要通过注册通知告知当前的网络状态了，在这里就要用到NSNotification
在下面的代码中，注册完通知后调用reachabilityChanged:方法，实现对网络的检测，更新网络显示状态。

- (void) applicationDidFinishLaunching: (UIApplication* )application 
{
    #pragma unused(application)
	contentView.backgroundColor = [UIColor groupTableViewBackgroundColor];
    
    summaryLabel.hidden = YES;        
    

    // Observe the kNetworkReachabilityChangedNotification. When that notification is posted, the
    // method "reachabilityChanged" will be called. 
    [[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.hopean.com"];
	hostReach = [[Reachability reachabilityWithHostName: @"www.hopesn.com"] retain];
	[hostReach startNotifier];
	[self updateInterfaceWithReachability: hostReach];
	
    internetReach = [[Reachability reachabilityForInternetConnection] retain];
	[internetReach startNotifier];
	[self updateInterfaceWithReachability: internetReach];

    wifiReach = [[Reachability reachabilityForLocalWiFi] retain];
	[wifiReach startNotifier];
	[self updateInterfaceWithReachability: wifiReach];

	[window makeKeyAndVisible];
    
}