AFNetworking

AFNetworkReachabilityManager是用來監測網絡狀態，網絡狀態管理的類，他可以通過設置狀態改變回調來獲得當前網絡狀態。

//網絡的狀態分四種
typedef NS_ENUM(NSInteger, AFNetworkReachabilityStatus) {
    AFNetworkReachabilityStatusUnknown          = -1,   //未知
    AFNetworkReachabilityStatusNotReachable     = 0,    //無網絡
    AFNetworkReachabilityStatusReachableViaWWAN = 1,    //蜂窩網絡
    AFNetworkReachabilityStatusReachableViaWiFi = 2,    //WiFi
};

一、屬性

公有屬性（.h中的）

// 當前網絡的狀態，就是枚舉中的類型
@property (readonly, nonatomic, assign) AFNetworkReachabilityStatus networkReachabilityStatus;
//當前網絡是否可用（蜂窩網或WiFi）
@property (readonly, nonatomic, assign, getter = isReachable) BOOL reachable;
//當前網絡是否是蜂窩網
@property (readonly, nonatomic, assign, getter = isReachableViaWWAN) BOOL reachableViaWWAN;
//當前網絡是否是WiFi
@property (readonly, nonatomic, assign, getter = isReachableViaWiFi) BOOL reachableViaWiFi;

私有屬性（.m中的）

//用來保存創建測試連接返回的引用
@property (readonly, nonatomic, assign) SCNetworkReachabilityRef networkReachability;
//網絡狀態
@property (readwrite, nonatomic, assign) AFNetworkReachabilityStatus networkReachabilityStatus;

二、初始化

AFNetworkReachabilityManager的初始化方法有5種
1、單例初始化

+ (instancetype)sharedManager {
    static AFNetworkReachabilityManager *_sharedManager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedManager = [self manager];   //調用了+ manager方法
    });

    return _sharedManager;
}

2、在第一個單例方法中調用了此方法，通過默認的socket地址初始化，返回一個manager對象，sin_family表示協議族，AF_INET表示TCP/IP協議族的地址。

+ (instancetype)manager
{
#if (defined(__IPHONE_OS_VERSION_MIN_REQUIRED) && __IPHONE_OS_VERSION_MIN_REQUIRED >= 90000) || (defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED >= 101100)
    struct sockaddr_in6 address;
    bzero(&address, sizeof(address));
    address.sin6_len = sizeof(address);
    address.sin6_family = AF_INET6;
#else
    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_len = sizeof(address);
    address.sin_family = AF_INET;
#endif
    return [self managerForAddress:&address];
}

3、在第二種方法里面又調用了此方法，通過傳入一個socket地址來初始化。

+ (instancetype)managerForAddress:(const void *)address {
    SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, (const struct sockaddr *)address);
    AFNetworkReachabilityManager *manager = [[self alloc] initWithReachability:reachability];

    CFRelease(reachability);
    
    return manager;
}

4、在第三種方法里面，又調用了第四種初始化方法，因為該方法的后綴里面有NS_DESIGNATED_INITIALIZER，所以最終都會調到它，這里就是做了初始化的工作，將起始的網絡狀態定為Unknown。

- (instancetype)initWithReachability:(SCNetworkReachabilityRef)reachability {
    self = [super init];
    if (!self) {
        return nil;
    }

    _networkReachability = CFRetain(reachability);
    self.networkReachabilityStatus = AFNetworkReachabilityStatusUnknown;

    return self;
}

5、這種方法就是可以根據特定的域來初始化。

+ (instancetype)managerForDomain:(NSString *)domain {
    SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(kCFAllocatorDefault, [domain UTF8String]);

    AFNetworkReachabilityManager *manager = [[self alloc] initWithReachability:reachability];
    
    CFRelease(reachability);

    return manager;
}

三、開始監聽、停止監聽

1、開始監聽方法

- (void)startMonitoring {
    [self stopMonitoring];

    if (!self.networkReachability) {
        return;
    }
    // 收到callback調用后，將status通過networkReachabilityStatusBlock回調出去
    __weak __typeof(self)weakSelf = self;
    AFNetworkReachabilityStatusBlock callback = ^(AFNetworkReachabilityStatus status) {
        __strong __typeof(weakSelf)strongSelf = weakSelf;

        strongSelf.networkReachabilityStatus = status;
        if (strongSelf.networkReachabilityStatusBlock) {
            strongSelf.networkReachabilityStatusBlock(status);
        }

    };
    // 聲明SCNetworkReachabilityContext結構體
    SCNetworkReachabilityContext context = {0, (__bridge void *)callback, AFNetworkReachabilityRetainCallback, AFNetworkReachabilityReleaseCallback, NULL};
    // 設置回調
    SCNetworkReachabilitySetCallback(self.networkReachability, AFNetworkReachabilityCallback, &context);
    // 加到Main runloop里面對其進行監測
    SCNetworkReachabilityScheduleWithRunLoop(self.networkReachability, CFRunLoopGetMain(), kCFRunLoopCommonModes);
    // 獲取當前的網絡狀態，調用callback
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0),^{
        SCNetworkReachabilityFlags flags;
        if (SCNetworkReachabilityGetFlags(self.networkReachability, &flags)) {
            AFPostReachabilityStatusChange(flags, callback);
        }
    });
}

2、停止監聽方法

- (void)stopMonitoring {
    if (!self.networkReachability) {
        return;
    }

    SCNetworkReachabilityUnscheduleFromRunLoop(self.networkReachability, CFRunLoopGetMain(), kCFRunLoopCommonModes);
}

四、應用（demo）

//監測網絡狀態的方法
- (void)monitorReachabilityStatus
{
    // 開始監測
    [[AFNetworkReachabilityManager sharedManager] startMonitoring];
    // 網絡狀態改變的回調
    [[AFNetworkReachabilityManager sharedManager] setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {
        switch (status) {
            case AFNetworkReachabilityStatusReachableViaWWAN:
                NSLog(@"蜂窩網絡");
                break;
            case AFNetworkReachabilityStatusReachableViaWiFi:
                NSLog(@"WIFI");
                break;
            case AFNetworkReachabilityStatusNotReachable:
                NSLog(@"沒有網絡");
                break;
            case AFNetworkReachabilityStatusUnknown:
                NSLog(@"未知");
                break;
            default:
                break;
        }
    }];
}