ESP8266无法通过mqtt主题发布更长的数据

我使用esp8266和Arduino IDE进行编程。当我试图通过wifi网络通过esp8266的MQTT主题发布JSON数据时，它适用于以下代码

void reportToServer(){
     String payload = "{\"DeviceID\":"+String(devices[0].getDeviceID())+","
                   "\"DeviceName\":"+"\""+String(devices[0].getDeviceName())+"\""+","
                   "\"Counter\":"+String(devices[0].getSwitchOnTime())+","
                   "\"Status\":"+String(devices[0].getStatus())+"};

    Serial.println(payload.c_str());
    client.publish("esp/test",payload.c_str());
    Serial.println("Reported to server");
}

但当我尝试发布如下代码时，MQTT.fxGUI客户端不会接收数据-

void reportToServer(){
     String payload = String payload = "{{\"DeviceID\":"+String(devices[0].getDeviceID())+","
                  "\"DeviceName\":"+"\""+String(devices[0].getDeviceName())+"\""+","
                  "\"Counter\":"+String(devices[0].getSwitchOnTime())+","
                  "\"Status\":"+String(devices[0].getStatus())+"},"+
                  "{\"DeviceID\":"+String(devices[1].getDeviceID())+","
                  "\"DeviceName\":"+"\""+String(devices[1].getDeviceName())+"\""+","
                  "\"Counter\":"+String(devices[1].getSwitchOnTime())+","
                  "\"Status\":"+String(devices[1].getStatus())+"}}";
                  +"{\"DeviceID\":"+String(devices[2].getDeviceID())+","
                  "\"DeviceName\":"+"\""+String(devices[2].getDeviceName())+"\""+","
                  "\"Counter\":"+String(devices[2].getSwitchOnTime())+","
                  "\"Status\":"+String(devices[2].getStatus())+"},"
                  +"{\"DeviceID\":"+String(devices[3].getDeviceID())+","
                  "\"DeviceName\":"+"\""+String(devices[3].getDeviceName())+"\""+","
                  "\"Counter\":"+String(devices[3].getSwitchOnTime())+","
                  "\"Status\":"+String(devices[3].getStatus())+"},"
                  +"{\"DeviceID\":"+String(devices[4].getDeviceID())+","
                  "\"DeviceName\":"+"\""+String(devices[4].getDeviceName())+"\""+","
                  "\"Counter\":"+String(devices[4].getSwitchOnTime())+","
                  "\"Status\":"+String(devices[4].getStatus())+"},"
                  +"{\"DeviceID\":"+String(devices[5].getDeviceID())+","
                  "\"DeviceName\":"+"\""+String(devices[5].getDeviceName())+"\""+","
                  "\"Counter\":"+String(devices[5].getSwitchOnTime())+","
                  "\"Status\":"+String(devices[5].getStatus())+"}}";

    Serial.println(payload.c_str());
    client.publish("esp/test",payload.c_str());
    Serial.println("Reported to server");
}

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正如评论中所讨论的那样

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有效载荷太大了。解决方案是使用publish_p方法。

第二个有效负载有多少字节，pubsub客户端头中有限制。有效负载的限制是什么？谢谢，最大大小是128字节。还有一种方法可以使用publish_p方法发布较长的消息，如库的README.md所示。