首先声明一下，我用的是 MQTTKit ，因为 MQTTClient 有一些问题，后台用的是混合主题，然后一直为空，无奈，换成了MQTTKit ，一次成功，再次表示感谢，对开源的大神们o(￣︶￣)o

直接上代码 ：
.h

#import <Foundation/Foundation.h>
#import "MQTTKit.h"

@interface mqttTool : NSObject

@property (nonatomic, strong) MQTTClient *client; // mqtt客户端
@property (nonatomic, strong) NSString *servicesState; // 服务开启状态
@property (nonatomic, strong) NSString *topicStr;  // 订阅主题内容
+ (instancetype)mqttManager;
- (void)connectToHost; // 连接mqtt 自动订阅
@end

.m

#import "mqttTool.h"

typedef enum : NSUInteger {
    MyMQTTScribeMessageRemoteUnlock,
    MyMQTTScribeMessageFingerVeinRegister,
    MyMQTTScribeMessageOther,
} MyMQTTScribeMessage;

@implementation mqttTool

+ (instancetype)mqttManager {
    static mqttTool *mqttToolInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        mqttToolInstance = [[mqttTool alloc] init];
    });
    return mqttToolInstance;
}

- (MQTTClient *)client {
    if (!_client) {
        NSString *clientID = [[UIDevice currentDevice] identifierForVendor].UUIDString;
        NSUserDefaults *users = [NSUserDefaults standardUserDefaults];
        NSString *userName    = [users objectForKey:kUserName];
        clientID = [NSString stringWithFormat:@"iOS%@",userName];
        _client = [[MQTTClient alloc] initWithClientId:clientID];
    }
    return _client;
}


#pragma mark - MQTT 订阅服务器通知内容
// 连接服务器
- (void)connectToHost {
    
    // 订阅获取消息
    [self setupMessageHandler];
    
    __weak typeof(self) weakSelf = self;
    // 异步连接服务器
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        // 设置连接到服务器的端口
        weakSelf.client.port = PORT_TG; // 切换成你们自己端口号
        // 开始连接 HOST_TG 切换成自己的服务器地址
        [weakSelf.client connectToHost:HOST_TG completionHandler:^(MQTTConnectionReturnCode code) {
            // 连接成功
            if (code == ConnectionAccepted) {
                
                weakSelf.servicesState = @"Service_ON";
                
                // 更新 UI
                dispatch_async(dispatch_get_main_queue(), ^{
                    // 转换为 CustomView 模式
                    [weakSelf subscribeTopic];
                });
                
            } else {
                dispatch_async(dispatch_get_main_queue(), ^{
//                    [weakSelf connectTimeoutAction];
                });
            }
        }];
        
    });
    
}

// 连接服务器超时触发动作
- (void)connectTimeoutAction {
    [SVProgressHUD dismiss];
    [requestTool showFailureMessage:@"远程开锁失败"];
}

#pragma mark - Subscribe / Unsubscribe
// 订阅某个主题
- (void)subscribeTopic {
    __weak typeof(self) weakSelf = self;
    NSString *uuidStr = [[[UIDevice currentDevice] identifierForVendor] UUIDString];
    _topicStr = [NSString stringWithFormat:@"/app/doorlock/%@/+",uuidStr]; // 这里是+号的话，可以订阅这里是任意字符的主题，但是不包括子路径
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        [weakSelf.client subscribe:weakSelf.topicStr withCompletionHandler:^(NSArray *grantedQos){
            // 更新 UI
            dispatch_async(dispatch_get_main_queue(), ^{
                // 返回订阅成功消息
//                [requestTool showSuccessMessage:@"订阅成功"];
            });
        }];
    });
}

// 取消订阅某个主题
- (void)unscribeTopic:(NSString *)topic atIndex:(NSIndexPath *)indexPath{
//    [requestTool showWaitMessage:@"取消订阅中..."];
    __weak typeof(self) weakSelf = self;
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        [weakSelf.client unsubscribe:topic withCompletionHandler:^{
            // 更新 UI
            dispatch_async(dispatch_get_main_queue(), ^{
                [requestTool showSuccessMessage:@"取消订阅成功"];
                //                sleep(1);
            });
        }];
    });
    
}
// 设置消息处理
- (void)setupMessageHandler {
    NSLog(@"%s", __func__);
    __weak typeof(self) weakSelf = self;
    [self.client setMessageHandler:^(MQTTMessage *message) {
        NSString *content  = message.payloadString;
        NSString *topicSt = message.topic;
        NSLog(@"text --->>%@ >>> %@", topicSt, content);
        NSString *purpose = [topicSt substringFromIndex:weakSelf.topicStr.length-1];
        NSError *error;
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:message.payload options:NSJSONReadingMutableContainers error:&error];
        NSString *resultStr = [NSString stringWithFormat:@"%@",dic[@"status"]];
        NSLog(@">>>%@",dic[@"status"]);
        // status 0 success 1 failure          
    }];
}


@end

如有疑问，可以直接问我，共同进步🙃