Вывод в виджет Activity из другого класса

Помогите с пониманием вопроса.

Есть MainActivity:

package ru.homeinn.iottank;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
private ConnectionMqtt connection = new ConnectionMqtt();
private Button mbtnmqtt;
public TextView mtext_mqtt;
private String NewString;
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}
public void onSettingsMenuClick(MenuItem item) {
    Intent intent = new Intent(MainActivity.this, ConfActivity.class);
    startActivity(intent);
}
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    connection.connect();
    mbtnmqtt = (Button) findViewById(R.id.btnmqtt);
    mtext_mqtt = (TextView) findViewById(R.id.info_text);

    mbtnmqtt.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            System.out.println("Onclick");
            connection.send();
        }
    });
    }
}

И есть ConnectionMqtt:

package ru.homeinn.iottank;
/**
 * Created by vit-j on 15.02.2017.
 */
import android.annotation.SuppressLint;
import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
public class ConnectionMqtt implements MqttCallback {
    MqttClient sampleClient = null;
    public ConnectionMqtt(){
    }
    public void connect(){
        try {
            String broker       = "tcp://m13.cloudmqtt.com:17546";
            String clientId     = "JavaSample";

            MemoryPersistence persistence = new MemoryPersistence();
            sampleClient = new MqttClient(broker, clientId, persistence);
            sampleClient.setCallback(new ConnectionMqtt());
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(true);
            connOpts.setUserName("");
            connOpts.setPassword("".toCharArray());
            System.out.println("Connecting to broker: "+broker);
            sampleClient.connect(connOpts);
            System.out.println("Connected");
            //System.out.println("Message published");
            sampleClient.subscribe("#");
            //sampleClient.disconnect();
            //System.out.println("Disconnected");
            //System.exit(0);
        } catch(MqttException me) {
            //System.out.println("reason "+me.getReasonCode());
            //System.out.println("msg "+me.getMessage());
            //System.out.println("loc "+me.getLocalizedMessage());
            //System.out.println("cause "+me.getCause());
            // System.out.println("excep "+me);
            me.printStackTrace();
        }
    }
    private static final String TAG = "MQTTService";

    public void send(){
        int qos             = 2;
        String topic        = "MQTT Examples";
        String content      = "Message from MqttPublishSample";
        System.out.println("Publishing message: "+content);
        MqttMessage message = new MqttMessage(content.getBytes());
        message.setQos(qos);
        try {
            sampleClient.publish(topic, message);
        } catch (MqttException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void connectionLost(Throwable throwable) {
        System.out.println("connectionLost!");
    }

    @Override
    @SuppressLint("NewApi")
    public void messageArrived(String topic, MqttMessage mqttMessage) throws Exception {
        System.out.println("Received message: "+topic + " message: " + mqttMessage);
        //mtext_mqtt.setText("Received message: "+topic + " message: " + mqttMessage);
    }
    @Override
    public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
        System.out.println("deliveryComplete: "+iMqttDeliveryToken);
    }

}

В ConnectionMqtt нужно по получению сообщения messageArrived обрабатывать полученные сообщения и выводить их в текстовые поля или менять значения визуальных компонентов в MainActivity.

Хотя бы так:

mtext_mqtt.setText("Received message: "+topic + " message: " + mqttMessage);

Но как правильно объявить mtext_mqtt = (TextView) findViewById(R.id.info_text) и передать в него данные не совсем понимаю. Как я понял этот класс не часть Activity

Вразумите в каком направлении двигаться и как правильно объявить.

Добавил стек трейс:

02-18 02:37:58.690 16678-16678/ru.homeinn.iottank E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to stop activity {ru.homeinn.iottank/ru.homeinn.iottank.MainActivity}: android.app.SuperNotCalledException: Activity {ru.homeinn.iottank/ru.homeinn.iottank.MainActivity} did not call through to super.onStop()
    at android.app.ActivityThread.handleSleeping(ActivityThread.java:2937)
    at android.app.ActivityThread.access$2600(ActivityThread.java:128)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1282)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4517)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
    at dalvik.system.NativeStart.main(Native Method)
 Caused by: android.app.SuperNotCalledException: Activity {ru.homeinn.iottank/ru.homeinn.iottank.MainActivity} did not call through to super.onStop()
    at android.app.Activity.performStop(Activity.java:4610)
    at android.app.ActivityThread.handleSleeping(ActivityThread.java:2934)
    at android.app.ActivityThread.access$2600(ActivityThread.java:128) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1282) 
    at android.os.Handler.dispatchMessage(Handler.java:99) 
    at android.os.Looper.loop(Looper.java:137) 
    at android.app.ActivityThread.main(ActivityThread.java:4517) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:511) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760) 
    at dalvik.system.NativeStart.main(Native Method)