I. MQTT

MQTT protocol is used in an Internet of things project, which can be used to communicate between devices and software

MQTT: instant messaging protocol, transport layer protocol

Two. Commonly used:

1. Mqttkit (no longer maintained)

2.MQTTClient

a. set address port, account password and other basic information

b. subscribe to topics (you can subscribe to multiple topics)

c. implement the proxy callback method (processing data)

Three message transmission modes: (depending on the situation)

a. at least one time (message loss or repetition will occur)

b. at least once (make sure the message arrives, and message repetition will occur)

c. only once (make sure the message arrives once)

Four. Code:

#import <MQTTClient/MQTTClient.h>
#import <MQTTClient/MQTTSessionManager.h>

Basic configuration information

- (void)setParameterWithManager
{
    /**
     host: server address
     port: Server port
     tls:  If tls protocol is used, mosca supports tls. If it is used, it should be set to true
     keepalive: Heartbeat time, in seconds, sending heartbeat packets every fixed time, heartbeat interval shall not be greater than 120s
     clean: session It needs to be noted whether to clear. If it is false, it means to keep the login. If the client logs in again offline, it can receive the offline message
     auth: Use login authentication or not
     user: User name
     pass: Password
     willTopic: Subscription theme
     willMsg: Customized offline messages
     willQos: Level of offline messages received
     clientId: Client id, it should be noted that this id needs to be globally unique, because the server distinguishes different clients according to this id. by default, after an id is logged in, if another connection is logged in with this id, the previous connection will be kicked out of the line. The UUID of the device I use
     */
    NSString *clientId = [UIDevice currentDevice].identifierForVendor.UUIDString;
    self.sessionManager = [[MQTTSessionManager alloc] init];
    [self.sessionManager connectTo:MQTTHOST
                              port:MQTTPORT
                               tls:false
                         keepalive:60  //Heartbeat interval shall not be greater than 120 s
                             clean:true
                              auth:true
                              user:MQTTUSERNAME
                              pass:MQTTPASSWORD
                              will:false
                         willTopic:nil
                           willMsg:nil
                           willQos:0
                    willRetainFlag:false
                      withClientId:clientId];
    self.sessionManager.delegate = self;

    // Add monitor state observer
    [self.sessionManager addObserver:self
                          forKeyPath:@"state"
                             options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
                             context:nil];
    // Subscription theme    NSDictionary Type, Object by QoS，key by Topic
    self.sessionManager.subscriptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:MQTTQosLevelExactlyOnce] forKey:@"Topics you want to subscribe to(Talk to the backstage)"];
}

Monitor connection status

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
{
    switch (self.sessionManager.state) {
        case MQTTSessionManagerStateClosed:
            NSLog(@"Connection closed");
            break;
        case MQTTSessionManagerStateClosing:
            NSLog(@"Connection closing");
            break;
        case MQTTSessionManagerStateConnected:
            NSLog(@"Already connected");
            break;
        case MQTTSessionManagerStateConnecting:
            NSLog(@"Connecting");
            break;
        case MQTTSessionManagerStateError: {
            NSString *errorCode = self.sessionManager.lastErrorCode.localizedDescription;
            NSLog(@"Connection exception ----- %@",errorCode);
        }
            break;
        case MQTTSessionManagerStateStarting:
            NSLog(@"Start connecting");
            break;
        default:
            break;
    }
}

Processing data

// Realization MQTTSessionManagerDelegate Agent method, processing data.
- (void)handleMessage:(NSData *)data onTopic:(NSString *)topic retained:(BOOL)retained
{
    NSLog(@"theme:%@",topic);
    NSString *dataString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSData * newData = [dataString dataUsingEncoding:NSUTF8StringEncoding];
    NSDictionary *jsonDict = [NSJSONSerialization JSONObjectWithData:newData options:NSJSONReadingMutableLeaves error:nil];
    NSLog(@"data:%@",jsonDict);
}

Finally, don't forget to remove the observer, otherwise the program will crash

[self.sessionManager removeObserver:self forKeyPath:@"state"];

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