How to get all selected checkbox from a ExpandableListView in Android?

I have an ExpandableListView that has groups and itens, each iten has a checkbox that can be selected and I want to know how can I iterate over all itens and get their values when I click the button.

So far I have created the list, I already can select the checkboxes and everything is going well, but I cant find a solution to get the values from the checkboxes when I click the button. This is like a questionary, when the user finishes picking his choices, he will submit the values.

I have a MainActivity, an ExpandableListAdapter that is my list adapter implementation and I have 3 xml, activity_main.xml, list_group.xml and list_itens.xml.

Here is my code so far:

public class ExpandableListAdapter extends BaseExpandableListAdapter {
private Context context;
private List<String> listaDePerguntas;
private HashMap<String, List<String>> listaDeRespostas;
private CheckBox check;   

public ExpandableListAdapter(Context context, List<String> listaDePerguntas, HashMap<String, List<String>> listaDeRespostas) {
    this.context = context;
    this.listaDePerguntas = listaDePerguntas;
    this.listaDeRespostas = listaDeRespostas;
}

@Override
public int getGroupCount() {
    return listaDePerguntas.size();
}

@Override
public int getChildrenCount(int groupPosition) {
    return listaDeRespostas.get(listaDePerguntas.get(groupPosition)).size();
}

@Override
public Object getGroup(int groupPosition) {
    return listaDePerguntas.get(groupPosition);
}

@Override
public Object getChild(int groupPosition, int childPosition) {
    return listaDeRespostas.get(listaDePerguntas.get(groupPosition)).get(childPosition);
}

@Override
public long getGroupId(int groupPosition) {
    return groupPosition;
}

@Override
public long getChildId(int groupPosition, int childPosition) {
    return childPosition;
}

@Override
public boolean hasStableIds() {
    return false;
}

@Override
public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
    String resposta = (String) getChild(groupPosition, childPosition);
    if(convertView == null) {
        LayoutInflater inflater = (LayoutInflater) this.context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.list_itens, null);
    }
    TextView text = (TextView) convertView.findViewById(R.id.listItem);
    text.setText(resposta);
    return convertView;
}

@Override
public View getChildView(final int groupPosition, final int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
    String resposta = (String) getChild(groupPosition, childPosition);

    if(convertView == null) {
        LayoutInflater inflater = (LayoutInflater) this.context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.list_itens, null);
    }
    TextView text = (TextView) convertView.findViewById(R.id.listItem);
    text.setText(resposta);

    CheckBox check = (CheckBox) convertView.findViewById(R.id.listCheckItem);
    //check.setFocusable(false);

    check.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            Toast.makeText(buttonView.getContext(), "Selected! - Question number: " + groupPosition + "answer: " + childPosition + "ischecked: " + isChecked, Toast.LENGTH_SHORT).show();

        }
    });
    return convertView;
}

@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
    return true;
}

}

My MainActivity class:

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private ExpandableListView listView;
    private ExpandableListAdapter listAdapter;

    private List<String> perguntas;
    private HashMap<String, List<String>> respostas;

    private Button enviarRespostas;

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

    listView = (ExpandableListView) findViewById(R.id.expandableListView);

    carregarDados();

    listAdapter = new ExpandableListAdapter(this, perguntas, respostas);
    listView.setAdapter(listAdapter);

    listView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {
        @Override
        public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {
            Toast.makeText(MainActivity.this, "Clicou no:" + groupPosition + " item: " + childPosition, Toast.LENGTH_SHORT).show();
            return false;
        }
    });

    listView.setOnGroupClickListener(new ExpandableListView.OnGroupClickListener() {
        @Override
        public boolean onGroupClick(ExpandableListView parent, View v, int groupPosition, long id) {
            Toast.makeText(MainActivity.this, "Clicou no:" + groupPosition, Toast.LENGTH_SHORT).show();
            return false;
        }
    });

    enviarRespostas = (Button) findViewById(R.id.buttonEnviarRespostas);
    enviarRespostas.setOnClickListener(this);

}


private void carregarDados() {
    perguntas = new ArrayList<>();
    respostas = new HashMap<>();

    perguntas.add("Pertunta 1");
    perguntas.add("Pertunta 2");
    perguntas.add("Pertunta 3");
    perguntas.add("Pertunta 4");

    List<String> respostasPergunta1 = new ArrayList<>();
    respostasPergunta1.add("Sim");
    respostasPergunta1.add("Não");
    respostasPergunta1.add("Talvez");

    List<String> respostasPergunta2 = new ArrayList<>();
    respostasPergunta2.add("10");
    respostasPergunta2.add("20");
    respostasPergunta2.add("30");
    respostasPergunta2.add("40");

    List<String> respostasPergunta3 = new ArrayList<>();
    respostasPergunta3.add("Sim");
    respostasPergunta3.add("Não");

    List<String> respostasPergunta4 = new ArrayList<>();
    respostasPergunta4.add("10");
    respostasPergunta4.add("20");
    respostasPergunta4.add("30");
    respostasPergunta4.add("40");
    respostasPergunta4.add("50");
    respostasPergunta4.add("60");

    respostas.put(perguntas.get(0), respostasPergunta1);
    respostas.put(perguntas.get(1), respostasPergunta2);
    respostas.put(perguntas.get(2), respostasPergunta3);
    respostas.put(perguntas.get(3), respostasPergunta4);
}

@Override
public void onClick(View v) {
    //todo
}

}

And here are my 3 .xml files:

1) activity_main.xml

<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:padding="10dp"
    android:weightSum="1">


<ExpandableListView
    android:id="@+id/expandableListView"
    android:layout_width="match_parent"
    android:layout_height="437dp" />

<Button
    android:id="@+id/buttonEnviarRespostas"
    android:layout_width="match_parent"
    android:layout_height="35dp"
    android:text="Button" />

</LinearLayout>

2) list_group.xml

<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="8dp"
    android:background="@android:color/white">

    <TextView
        android:id="@+id/header"
        android:paddingLeft="?
        android:attr/expandableListPreferredItemPaddingLeft"
        android:textSize="16dp"
        android:textColor="@android:color/black"
        android:layout_width="match_parent"
        android:layout_height="/>

</LinearLayout>

3) list_itens.xml

<TableLayout xmlns:android="http://ift.tt/nIICcg"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:stretchColumns="0">

    <TableRow>
        <TextView
            android:id="@+id/listItem"
            android:textSize="16dp"
            android:paddingLeft="?
            android:attr/expandableListPreferredChildPaddingLeft"
            android:paddingTop="5dp"
            android:paddingBottom="5dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
        <CheckBox
            android:id="@+id/listCheckItem"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginRight="50dp" />
    </TableRow>
</TableLayout>