确定iPhone上的互联网可用性？

我在iPhone应用程序中使用NSURLConnection,如下所示:

NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest: request delegate: self];

请求已设置并正常工作,但我希望能够在没有可用连接的情况下向用户提供"连接不可用"消息.有没有快速的方法来确定iPhone上是否有可用的Internet连接？

像启动NSURLConnection后添加以下内容一样简单:

if (conn) { // do normal processing } else { // display connection not available message }

提前谢谢,本

这对我有用,取自苹果地震xml项目:

- (BOOL)isDataSourceAvailable
{
    static BOOL checkNetwork = YES;
    if (checkNetwork) { // Since checking the reachability of a host can be expensive, cache the result and perform the reachability check once.
        checkNetwork = NO;

        Boolean success;    
        const char *host_name = "twitter.com"; // your data source host name

        SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(NULL, host_name);
        SCNetworkReachabilityFlags flags;
        success = SCNetworkReachabilityGetFlags(reachability, &flags);
        _isDataSourceAvailable = success && (flags & kSCNetworkFlagsReachable) && !(flags & kSCNetworkFlagsConnectionRequired);
        CFRelease(reachability);
    }
    return _isDataSourceAvailable;
}