1.虽然各种直接获取信号强度的api都被封杀了。但是还有一个另类的黑魔法可以获取到。那就是遍历UIStatusBar了

//获取网络信号强度（dBm）
- (int)getSignalStrength{
    if (iPhoneX) {
        id statusBar = [[UIApplication sharedApplication] valueForKeyPath:@"statusBar"];
        id statusBarView = [statusBar valueForKeyPath:@"statusBar"];
        UIView *foregroundView = [statusBarView valueForKeyPath:@"foregroundView"];
        int signalStrength = 0;
        
        NSArray *subviews = [[foregroundView subviews][2] subviews];
        
        for (id subview in subviews) {
            if ([subview isKindOfClass:NSClassFromString(@"_UIStatusBarWifiSignalView")]) {
                signalStrength = [[subview valueForKey:@"numberOfActiveBars"] intValue];
                break;
            }else if ([subview isKindOfClass:NSClassFromString(@"_UIStatusBarStringView")]) {
                signalStrength = [[subview valueForKey:@"numberOfActiveBars"] intValue];
                break;
            }
        }
        return signalStrength;
    } else {
        
        UIApplication *app = [UIApplication sharedApplication];
        NSArray *subviews = [[[app valueForKey:@"statusBar"] valueForKey:@"foregroundView"] subviews];
        NSString *dataNetworkItemView = nil;
        int signalStrength = 0;
        
        for (id subview in subviews) {
            
            if([subview isKindOfClass:[NSClassFromString(@"UIStatusBarDataNetworkItemView") class]] && [[self getNetworkType] isEqualToString:@"WIFI"] && ![[self getNetworkType] isEqualToString:@"NONE"]) {
                dataNetworkItemView = subview;
                signalStrength = [[dataNetworkItemView valueForKey:@"_wifiStrengthBars"] intValue];
                break;
            }
            if ([subview isKindOfClass:[NSClassFromString(@"UIStatusBarSignalStrengthItemView") class]] && ![[self getNetworkType] isEqualToString:@"WIFI"] && ![[self getNetworkType] isEqualToString:@"NONE"]) {
                dataNetworkItemView = subview;
                signalStrength = [[dataNetworkItemView valueForKey:@"_signalStrengthRaw"] intValue];
                break;
            }
        }
        return signalStrength;
    }
}

-(void)displayWifiViewWithNetStatus:(NSInteger)networkStatus {
    
    switch (networkStatus) {
        case 1:
            self.networkView.image = [UIImage imageNamed:@"ic_WiFi-3"];
            break;
        case 2:
            self.networkView.image = [UIImage imageNamed:@"ic_WiFi-2"];
            break;
        case 3:
            self.networkView.image = [UIImage imageNamed:@"ic_WiFi-1"];
            break;
            
        default:
            self.networkView.image = [UIImage imageNamed:@"ic_WiFi-1"];
            break;
    }
}

//检查当前是否连网
- (BOOL)whetherConnectedNetwork
{
    //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_storage zeroAddress;//IP地址
    
    bzero(&zeroAddress, sizeof(zeroAddress));//将地址转换为0.0.0.0
    zeroAddress.ss_len = sizeof(zeroAddress);//地址长度
    zeroAddress.ss_family = AF_INET;//地址类型为UDP, TCP, etc.
    
    // Recover reachability flags
    SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);
    SCNetworkReachabilityFlags flags;
    
    //获得连接的标志
    BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
    CFRelease(defaultRouteReachability);
    
    //如果不能获取连接标志，则不能连接网络，直接返回
    if (!didRetrieveFlags)
    {
        return NO;
    }
    //根据获得的连接标志进行判断
    
    BOOL isReachable = flags & kSCNetworkFlagsReachable;
    BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;
    return (isReachable&&!needsConnection) ? YES : NO;
}

//获取网络类型
- (NSString *)getNetworkType {
    if (![self whetherConnectedNetwork]) return @"NONE";
    UIApplication *app = [UIApplication sharedApplication];
    NSArray *subviews = [[[app valueForKeyPath:@"statusBar"] valueForKeyPath:@"foregroundView"] subviews];
    NSString *type = @"NONE";
    for (id subview in subviews) {
        if ([subview isKindOfClass:NSClassFromString(@"UIStatusBarDataNetworkItemView")]) {
            int networkType = [[subview valueForKeyPath:@"dataNetworkType"] intValue];
            switch (networkType) {
                case 0:
                    type = @"NONE";
                    break;
                case 1:
                    type = @"2G";
                    break;
                case 2:
                    type = @"3G";
                    break;
                case 3:
                    type = @"4G";
                    break;
                case 5:
                    type = @"WIFI";
                    break;
            }
        }
    }
    return type;
}

2.还有一种使用NetworkExtension/NEHotspotHelper来获取WIFI信息。但是得向苹果申请权限。感兴趣可以研究研究。

参考：http://www.cocoachina.com/ios/20180124/21965.html