View Model

ListActivity.java

package com.example.mysensor;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

import com.example.mysensor.model.Sensor;

import java.util.List;
import java.util.Random;

public class ListActivity extends AppCompatActivity implements SensorListDisplayLogic {

    private SensorListViewModel viewModel;

    private ProgressBar progressBar;

    private LinearLayout linearLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list);

        linearLayout = findViewById(R.id.linearLayout);
        progressBar = findViewById(R.id.progressBar2);

        viewModel = new MySensorListViewModel(this);
        viewModel.requestSensorList();

        //setupCustomView();
        //setupRows();
    }

    private void setupCustomView() {
        View sensorView;
        TextView textView;

        for (int i = 0; i < 10; i++) {

            sensorView = getLayoutInflater().inflate(R.layout.view_sensor, linearLayout, false);
            textView = sensorView.findViewById(R.id.tvSensor);
            textView.setText("Sensor " + i);

            linearLayout.addView(sensorView);
        }
    }

    private void setupRows() {
        Random random = new Random();

        for (int i = 0; i < 100; i++) {

            TextView blue = new TextView(this);
            blue.setText("World" + i);
            blue.setBackgroundColor(
                    Color.rgb(
                            random.nextInt(255), random.nextInt(255), random.nextInt(255)));
            blue.setTextSize(30);

            linearLayout.addView(blue,
                    LinearLayout.LayoutParams.MATCH_PARENT);
        }
    }

    @Override
    public void displaySensorList(List<Sensor> list) {
        progressBar.setVisibility(View.GONE);
        setTitle("MySensors");

        linearLayout.removeAllViews();

        View sensorView;
        TextView textView;

        for (Sensor sensor : list) {
            sensorView = getLayoutInflater().inflate(R.layout.view_sensor, linearLayout, false);
            textView = sensorView.findViewById(R.id.tvSensor);
            textView.setText(String.format("Sensor %d", sensor.getId()));
            linearLayout.addView(sensorView);
        }
    }

    @Override
    public void displayLoading() {
        setTitle("Carregando...");
        progressBar.setVisibility(View.VISIBLE);
    }

    @Override
    public void displayError(String error, int code) {
        Toast.makeText(this, String.format("%s - %d", error, code), Toast.LENGTH_SHORT).show();
    }
}

MySensorListViewModel.java

package com.example.mysensor;

import android.os.Handler;

import com.example.mysensor.model.Sensor;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class MySensorListViewModel implements SensorListViewModel {

    private Handler handler = new Handler();
    private List<Sensor> sensors = new ArrayList();
    private SensorListDisplayLogic displayLogic;

    MySensorListViewModel(SensorListDisplayLogic displayLogic) {
        this.displayLogic = displayLogic;
        sensors.add(new Sensor(1, "Cozinha"));
        sensors.add(new Sensor(2, "Quarto"));
    }

    @Override
    public void requestSensorList() {
        final Random random = new Random();
        displayLogic.displayLoading();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                if(random.nextInt(4) == 3) {
                    displayLogic.displayError("Algo deu errado", 100);
                } else {
                    displayLogic.displaySensorList(sensors);
                }
            }
        }, 5000);
    }
}

Sensor.java

package com.example.mysensor.model;

public class Sensor {
    private final int id;
    private final String tag;

    public Sensor(int id, String tag) {
        this.id = id;
        this.tag = tag;
    }

    public int getId() {
        return id;
    }

    public String getTag() {
        return tag;
    }
}

SensorListDisplayLogic.java

package com.example.mysensor;

import com.example.mysensor.model.Sensor;

import java.util.List;

public interface SensorListDisplayLogic {

    void displaySensorList(List<Sensor> list);

    void displayLoading();

    void displayError(String error, int code);
}

SensorListViewModel.java

package com.example.mysensor;

public interface SensorListViewModel {

    void requestSensorList();
}