使用MQTTKit向服务器发送消息

1. 通过Cocoa Pods添加MQTTKit

MQTTKit在github上链接https://github.com/NormanLeeIOS/MQTTKit#send-a-message，down下来。

cd到工程目录，输入pod install，用xcode打开工程的打开xcworkspace扩展名的文件。

如果不是MQTTKit存在更新的版本，则输入pod update。

2、连接过程

• 新建一个MQTT的服务请求

NSString *clientID = ...
MQTTClient *client = [[MQTTClient alloc] initWithClientId:clientID];

• 发送消息，每次发送消息包括目标host和本地MQTT消息.具体MQTT格式消息见代码。这里Host可以是Server的IP，不需要host表解析。

// connect to the MQTT server
[self.client connectToHost:@"iot.eclipse.org"
         completionHandler:^(NSUInteger code) {
    if (code == ConnectionAccepted) {
        // when the client is connected, send a MQTT message
        [self.client publishString:@"Hello, MQTT"
                           toTopic:@"/MQTTKit/example"
                           withQos:AtMostOnce
                            retain:NO
                 completionHandler:^(int mid) {
            NSLog(@"message has been delivered");
        }];
    }
}];

• 订阅主题并接受MQTT格式的消息，这部分在viewdidload中实现。

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

// connect the MQTT client
[self.client connectToHost:@"iot.eclipse.org"
         completionHandler:^(MQTTConnectionReturnCode code) {
    if (code == ConnectionAccepted) {
        // when the client is connected, subscribe to the topic to receive message.
        [self.client subscribe:@"/MQTTKit/example"
         withCompletionHandler:nil];
    }
}];

• 断开连接

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

整个连接建立、发送消息、接受消息、断开连接都是通过Block的消息机制来实现，因此需要对block有很好地理解。

具体各个消息机制解析见：http://www.cocoachina.com/industry/20131216/7543.html