Why can't we use PubSub Clinet library with this ESP_WiFiManager lib?

[MEHUL95]

The biggest prob I faced is with pointers and objects. Your mqtt example code uses pointers and clears it to create new instances, but the same we cannot do if we do not use pointers.

The main point is that pubsub client lib accepts reference while Adafruit mqtt lib accepts pointers.

Adafruit_MQTT_Client.h

class Adafruit_MQTT_Client : public Adafruit_MQTT 
{
public:
  Adafruit_MQTT_Client(Client *client, const char *server, uint16_t port,
                       const char *cid, const char *user, const char *pass)
      : Adafruit_MQTT(server, port, cid, user, pass), client(client) {}`

PubSubclient.cpp

PubSubClient::PubSubClient(Client& client) 
{
    this->_state = MQTT_DISCONNECTED;
    setClient(client);
    this->stream = NULL;
    this->bufferSize = 0;
    setBufferSize(MQTT_MAX_PACKET_SIZE);
    setKeepAlive(MQTT_KEEPALIVE);
    setSocketTimeout(MQTT_SOCKET_TIMEOUT);
}

So, the pointer that you are using to delete and create a new instance, I cannot do the same with PubSub client lib, can you please help here?

Showcasing short part of the code that I tried and failed.

WiFiClient *espClient   = NULL;
PubSubClient *clientnew = NULL;`

void deleteOldInstances()
{
  // Delete previous instances
  if (clientnew)
  {
    delete clientnew;
    clientnew = NULL;
    
    Serial.println(F("Deleting old MQTT object"));
  }
}

void createNewInstances()
{
  if (!espClient)
  {
    espClient = new WiFiClient;
    
    Serial.print(F("\nCreating new WiFi client object : "));
    Serial.println(espClient? F("OK") : F("failed"));
  }
  
  // Create new instances from new data
  if (!clientnew)
  {
    clientnew = new PubSubClient(espClient);
    // Setup the MQTT client class by passing in the WiFi client and MQTT server and login details.
    //clientnew = new PubSubClient(espClient, mqtt_server, atoi(mqtt_port), mqtt_User, mqtt_Password);
    
    Serial.print(F("Creating new MQTT object : "));
    
    if (clientnew)
    {
      Serial.println(F("OK"));
      Serial.println(String("mqtt_server = ")    + mqtt_server    + ", mqtt_port = "  + mqtt_port);
      Serial.println(String("mqtt_User = ")  + mqtt_User  + ", mqtt_Password = "         + mqtt_Password);
    }
    else
      Serial.println(F("Failed"));
  }
}

[khoih-prog]

You certainly can use with anything or any library in normal running, provided that you write the correct code.

Because this is just a simple programming knowledge (pointer, instance, etc.), I suggest you try fix the issue yourself and learn a lot thru the experience to benefit in the long run.

You can also post the request for help on Arduino Forum

Good Luck,