1,引入MqttSDK.

2,在Appdelegare中引入头
#import "MQTTSession.h"
 #import "MQTTViewController.h"

//定义主题
#define kTopic @"lichanghong"
//服务器ip
#define kIP @"192.168.2.204"

@interface SWAppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

@property (readonly, strong, nonatomic) NSString *currentUser;

- (void)saveContext;

- (NSURL *)applicationDocumentsDirectory;

- (void)login;

- (void)connectToServer;

- (void)sendMessage:(NSString *)message toUser:(NSString *)toUser;

+ (SWAppDelegate *)shareInstance;

@end

//定义一属性

@interface SWAppDelegate ()

@property (nonatomic, strong) MQTTSession *session;

@end

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  MQTTViewController *mqttVC = [[MQTTViewController alloc]init];
  mqttVC.view.backgroundColor = [UIColor whiteColor];
  self.window.rootViewController = mqttVC;
   return YES;
}

所有实现代码都在MQTTViewController里

#import "MQTTSession.h"
#import "Message+Parser.h"

@implementation MQTTViewController
{
  MQTTSession *session;
}

- (void)viewDidLoad {
    [super viewDidLoad];
   
//  //连接
  session = [[MQTTSession alloc] initWithClientId:@"12345"];
  [session setDelegate:self];
  [session connectToHost:@"192.168.2.204" port:1883];
//
//   [session publishDataAtLeastOnce:[@"publish data..." dataUsingEncoding:NSUTF8StringEncoding] onTopic:@"lichanghong"];
    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


#pragma mark - MQtt Callback methods

- (void)session:(MQTTSession*)sender handleEvent:(MQTTSessionEvent)eventCode {
  switch (eventCode) {
    case MQTTSessionEventConnected:
      [session subscribeTopic:@"lichanghong"];
      NSLog(@"connected");

      break;
    case MQTTSessionEventConnectionRefused:
      NSLog(@"connection refused");
      break;
    case MQTTSessionEventConnectionClosed:
      NSLog(@"connection closed");
      break;
    case MQTTSessionEventConnectionError:
      NSLog(@"connection error");
      NSLog(@"reconnecting...");
      // Forcing reconnection
      [session connectToHost:kIP port:1883];
      break;
    case MQTTSessionEventProtocolError:
      NSLog(@"protocol error");
      break;
  }
}

- (void)session:(MQTTSession*)sender  newMessage:(NSData*)data  onTopic:(NSString*)topic {
  NSLog(@"new message, %lu bytes, topic=%@", (unsigned long)[data length], topic);
  NSString *payloadString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
  NSLog(@"data: %@ %@", payloadString, data);
  [Message parseMessage:data];
 
}

MQTT实现长连接,IM最简单实例