用SCNetworkReachability判断联网状态

1、判断手机是否连接到网络，iOS提供了一个SCNetworkReachabilityRef类，方便我们的使用。
2、创建一个工具类，方便全局调用

.h

#import <Foundation/Foundation.h>

@interface NetworkUtil : NSObject

+ (BOOL)isNetworkReachable;

@end

.m

#import "NetworkUtil.h"
#import <SystemConfiguration/SCNetworkReachability.h>
#import <netdb.h>

@implementation NetworkUtil

// networkチェック
+ (BOOL)isNetworkReachable
{
    // Create zero addy
    //创建零地址，0.0.0.0的地址表示查询本机的网络连接状态
    struct sockaddr_in zeroAddress;
    bzero(&zeroAddress, sizeof(zeroAddress));
    zeroAddress.sin_len = sizeof(zeroAddress);
    zeroAddress.sin_family = AF_INET;

    // Recover reachability flags
    // SCNetworkReachabilityFlags：保存返回的测试连接状态
    // 其中常用的状态有：
    // kSCNetworkReachabilityFlagsReachable：能够连接网络
    // kSCNetworkReachabilityFlagsConnectionRequired：能够连接网络，但是首先得建立连接过程
    // kSCNetworkReachabilityFlagsIsWWAN：判断是否通过蜂窝网覆盖的连接，比如EDGE，GPRS或者目前的3G.主要是区别通过WiFi的连接。
    SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL,
        (struct sockaddr*)&zeroAddress);
    SCNetworkReachabilityFlags flags;

    BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
    CFRelease(defaultRouteReachability);

    if (!didRetrieveFlags) {
        return NO;
    }

    BOOL isReachable = flags & kSCNetworkFlagsReachable;
    BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;
    return (isReachable && !needsConnection) ? YES : NO;
}

@end

使用

#import "ViewController.h"
#import "NetworkUtil.h"


@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    BOOL result = [NetworkUtil isNetworkReachable];
    NSLog(@"是否可以联网：%@",result?@"YES":@"NO");
}
@end