1. 下载MQTTKIT开源库，编译出你所需要的libMQTTKit.a和头文件

MQTTKIT开源库github下载地址：点这里

下载好MQTTKIT开源库后，编译下（假如你想在模拟器上运行客户端，可以直接编译出一个模拟器版本的libMQTTKit.a和头文件，反之编译出一个手机客户端版本）

编译好的文件截图：

2. MQTT客户端设计（连接服务器，发布话题，订阅话题）

新建一个关于mqtt的xcode工程，然后将上面编译好的libMQTTKit.a和头文件拖到工程中去

然后新建一个类，用做连接测试用，具体代码如下：

（也可以参考这个github大神写的demo：地址）

@implementation LJMQTTViewController

- (void)dealloc
{
    // disconnect the MQTT client
    [self.client disconnectWithCompletionHandler:^(NSUInteger code) {
        // The client is disconnected when this completion handler is called
        NSLog(@"MQTT is disconnected");
    }];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self initMqttSerive];
    [self createBulletButton];
}

- (void)createBulletButton
{
    UIButton *_ljBtn = [[UIButton alloc]init];
    [_ljBtn setFrame:CGRectMake((screenFrame.size.width - 150)/2.0, (screenFrame.size.height - 50)/2.0 + 120, 150, 50)];
    _ljBtn.backgroundColor = [UIColor grayColor];
    [_ljBtn setTitle:@"Bullet test" forState:UIControlStateNormal];
    [_ljBtn addTarget:self action:@selector(ljBulletBtnClicked) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:_ljBtn];
}

- (void)initMqttSerive
{
    // create the MQTT client with an unique identifier
    NSString *clientID = [UIDevice currentDevice].identifierForVendor.UUIDString;
    self.client = [[MQTTClient alloc] initWithClientId:clientID];
    
    // keep a reference on the switch to avoid having a reference to self in the
    // block below (retain/release cycle, blah blah blah)
   // UISwitch *subSwitch = self.subscribedSwitch;
    
    // define the handler that will be called when MQTT messages are received by the client
    [self.client setMessageHandler:^(MQTTMessage *message) {
        // extract the switch status from the message payload
        BOOL on = [message.payloadString boolValue];
        
        // the MQTTClientDelegate methods are called from a GCD queue.
        // Any update to the UI must be done on the main queue
        dispatch_async(dispatch_get_main_queue(), ^{
            //[subSwitch setOn:on animated:YES];
        });
    }];
    
    // connect the MQTT client
    [self.client connectToHost:kMQTTServerHost completionHandler:^(MQTTConnectionReturnCode code) {
        if (code == ConnectionAccepted) {
            // The client is connected when this completion handler is called
            NSLog(@"client is connected with id %@", clientID);
            [self subscribeTop:kTopic];
        }
    }];
    
    //获取话题消息回调
    //[self handleMqttMessage];
}

- (void)ljBulletBtnClicked
{
    [self publishString:@"test"];
}

#pragma mark -- 订阅话题
- (void)subscribeTop:(NSString*)topicStr
{
    // Subscribe to the topic
    [self.client subscribe:topicStr withCompletionHandler:^(NSArray *grantedQos) {
        // The client is effectively subscribed to the topic when this completion handler is called
        NSLog(@"subscribed to topic %@", kTopic);
    }];
}

#pragma mark -- 发布
- (void)publishString:(NSString*)payload
{
    // use the MQTT client to send a message with the switch status to the topic
    [self.client publishString:payload
                       toTopic:kTopic
                       withQos:AtMostOnce
                        retain:YES
             completionHandler:nil];
    // we passed nil to the completionHandler as we are not interested to know
    // when the message was effectively sent
}

#pragma mark -- received message
- (void)handleMqttMessage
{
    // define the handler that will be called when MQTT messages are received by the client
    [self.client setMessageHandler:^(MQTTMessage *message)
     {
        NSLog(@"received message %@", message.payloadString);
    }];
}

从上面的log可以看出，当你连接服务器成功后，服务器会给你返回一个唯一的id，当服务端想给你推消息时，可以根据你的这个唯一id来推给你

我此处订阅的话题是“#”，它代表服务器上所有的话题消息，我都可以接收到。

3. 通过PHP网页来向客户端发送一个话题（此处的服务器就是上一篇搭建的mosquitto）

PHP发送消息的截图（http://localhost/PhpM/index.php）：

PHP的MQTT环境搭建见我的这篇文章：地址

IOS MQTT客户端接收到的消息截图：