Implementação de uma lista de perguntas com resposta multi-escolha. usando ExpandableListView

activity_main-xml

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin">

    <TextView
        android:id="@+id/textView"
        android:text="Questionário"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="32dp"/>

    <ExpandableListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/expandableListView"
        android:layout_below="@+id/textView"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
</RelativeLayout>

Answer.java

//Responsável por guardar o texto da resposta. 
public class Answer {

    private final String answerText;

    public Answer(String text){
        this.answerText = text;
    }

    public String getText() {
        return answerText;
    }
}  

answer_row.xml

<!--View para as respostas, representa cada um dos sub-itens dentro de cada grupo da ExpandableListView.-->
<!--Contém um RadioButton com o texto da resposta.-->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="16dp">

    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New RadioButton"
        android:id="@+id/answerText"
        android:clickable="false"
        android:focusable="false"/>
</LinearLayout>

ExpandListAdapter.java

//Responsável por fazer a ponte entre os dados e a ExpandableListView
public class ExpandListAdapter extends BaseExpandableListAdapter {

    private final LayoutInflater inflater;;
    private ArrayList<Question> questions;

    public ExpandListAdapter(Context context, ArrayList<Question> questions){
        inflater = LayoutInflater.from(context);
        this.questions = questions;
    }

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

    @Override
    public int getChildrenCount(int groupPosition) {
        ArrayList<Answer> answers = questions.get(groupPosition).getAnswers();
        if(answers == null){
            return 0;
        }
        return questions.get(groupPosition).getAnswers().size();
    }

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

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return questions.get(groupPosition).getAnswers().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 getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {

        View row = convertView;
        ViewHolder holder;

        if (row == null)
        {
            row = inflater.inflate(R.layout.question_row, parent, false);
            holder = new ViewHolder();
            holder.addView(row.findViewById(R.id.questionText))
                  .addView(row.findViewById(R.id.correctMark));
            row.setTag(holder);
        }else{
            holder = (ViewHolder) row.getTag();
        }

        TextView questionText = (TextView) holder.getView(R.id.questionText);
        CheckBox correctMark = (CheckBox) holder.getView(R.id.correctMark);
        Question question = questions.get(groupPosition);

        if(question.isCorrectlyAnswered()) {
            correctMark.setVisibility(View.VISIBLE);
        }else {
            correctMark.setVisibility(View.GONE);
        }

        questionText.setText(question.getText());
        return row;

    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {

        View row = convertView;
        ViewHolder holder;

        if (row == null)
        {
            row = inflater.inflate(R.layout.answer_row, parent, false);
            holder = new ViewHolder();
            holder.addView(row.findViewById(R.id.answerText));
            row.setTag(holder);
        }else{
            holder = (ViewHolder) row.getTag();
        }

        RadioButton answerText = (RadioButton) holder.getView(R.id.answerText);

        if(questions.get(groupPosition).getSelectedAnswer() == childPosition){
            answerText.setChecked(true);
        }else{
            answerText.setChecked(false);
        }
        answerText.setText(questions.get(groupPosition).getAnswers().get(childPosition).getText());

        return row;
    }

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

    static class ViewHolder
    {
        private HashMap<Integer, View> storedViews = new HashMap<Integer, View>();

        public ViewHolder addView(View view)
        {
            int id = view.getId();
            storedViews.put(id, view);
            return this;
        }

        public View getView(int id)
        {
            return storedViews.get(id);
        }
    }
}

MainActivity.java

Public class MainActivity extends AppCompatActivity {

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

        //Obtém a referência da ExpandableListView
        ExpandableListView expListView = (ExpandableListView) findViewById(R.id.expandableListView);

        //Obtém a lista de perguntas a ser apresentada
        final ArrayList<Question> questions = getQuestions();

        //Cria uma instância do adapter e atribui-o à ExpandableListView
        expListView.setAdapter(new ExpandListAdapter(this, questions));

        //Define um listener para tratar a selecção das respostas
        expListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {

            @Override
            public boolean onChildClick(ExpandableListView parent, View v,
                                        int groupPosition, int childPosition, long id) {

                //Indica que esta resposta foi seleccionada
                questions.get(groupPosition).setSelectedAnswer(childPosition);

                //Obtém a referência do adapter
                ExpandListAdapter adapter = (ExpandListAdapter) parent.getExpandableListAdapter();

                //Notifica o adapter da selecção para que ela seja representada visualmente
                adapter.notifyDataSetChanged();
                return true;
            }
        });
    }

    //Preenche um ArrayList com 10 perguntas e respectivas respostas
    private ArrayList<Question> getQuestions() {
        ArrayList<Question> questions = new ArrayList<>();
        Question question;
        int totalAnswers;
        Random rnd = new Random();

        for (int i = 1; i <= 10; i++){
            question = new Question("Question - " + i);
            //As perguntas pares têm 3 respostas as impar 5
            if(i%2 == 0){
                totalAnswers = 3;
            }else{
                totalAnswers = 5;
            }
            for (int j = 1; j <= totalAnswers; j++){
                question.addAnswer("Answer - " + j + " to question - " + i);
            }
            //Atribui aleatóriamente a resposta correcta
            question.setCorrectAnswer(rnd.nextInt(totalAnswers));
            questions.add(question);
        }

        return questions;
    }
}

Question.java

//Responsável por guardar o texto da pergunta, as respostas, a resposta correcta e a resposta seleccionada
public class Question {

    private final String questionText;
    private ArrayList<Answer> answers;
    private int selectedAnswer = -1;
    private int correctAnswer = -1;

    public Question(String text) {
        this.questionText = text;
        answers = new ArrayList<>();
    }

    public boolean isCorrectlyAnswered(){
        return correctAnswer == getSelectedAnswer();
    }

    public int getSelectedAnswer() {
        return selectedAnswer;
    }

    public void setSelectedAnswer(int selectedAnswer) {
        this.selectedAnswer = selectedAnswer;
    }


    public void setCorrectAnswer(int correctAnswer) {
        if(answers.size() <= correctAnswer){
            throw new IllegalArgumentException();
        }
        this.correctAnswer = correctAnswer;
    }

    public void addAnswer(String text){
        answers.add(new Answer(text));
    }

    public String getText(){
        return questionText;
    }

    public ArrayList<Answer> getAnswers(){
        return answers;
    }
}

question_row.xml

<!-- View para as perguntas, representa cada um dos grupos da ExpandableListView.-->
<!-- Contém o texto da pergunta e um sinal para indicar se a pergunta foi correctamente respondida.-->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.CardView
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:id="@+id/card_view"
        android:layout_gravity="center"
        android:layout_width="match_parent"
        android:layout_height="75dp"
        card_view:cardCornerRadius="4dp">

        <TextView
            android:id="@+id/questionText"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="questionText"/>
        <CheckBox
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/correctMark"
            android:layout_gravity="right"
            android:clickable="false"
            android:focusable="false"
            android:checked="true"
            android:visibility="gone"/>
    </android.support.v7.widget.CardView>

</LinearLayout>