Question

I have a very peculiar problem. I understand that while in the foreground the member variables of an Activity remain untouched (don’t need saving to persist). Now, I have a PagerAdapter that represents a quiz with a question and three answers. I’ve made various objects to represent the question and answers.

A Question always has a list of exactly 3 Answer‘s. This is how I do it: (note: some code was left out for readability)

public class QuizPagerAdapter
{
    List<Question> questionList;
    Context context;

    public QuizPagerAdapter (List<Question> list, Context ctx) {
        questionList = list;
        context = ctx;
    }

    @Override
    public Object instantiateItem (View pager, int position) {
        // Create various views (ScrollView, LinearLayout, etc)

        final Question q = questionList.get(position);

        RadioGroup group = new RadioGroup(context);
        for (int i = 0; i < 3; i++) {
            Answer a = q.getAnswer(i);

            RadioButton rb = new RadioButton(context);
            rb.setId(i);
            rb.setText(a.getText());

            rb.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    RadioButton btn = (RadioButton) v;
                    q.unselectAll(); // unselects all Answer's


                    q.getAnswer(btn.getId()).setSelected(true);
                }
            });

            if (a.isSelected()) rb.setChecked(true);
        }
        return view;
    }
}

When I use this in my Activity, I get a nice list of Questions with three Answers. Now, when I select one Answer, the RadioButton is checked. OK, now, I scroll to the next Question and check that one, then go back to the previous Question and there the answer I checked in the first place is now not checked.

Now, this doesn’t always happen, it happens sometimes, but that sometimes is enough that it can cause a problem. The Activity is never placed in the background.

I understand that Android will destroy Views in the PagerAdapter to conserve memory, thus destroying the RadioButton, this is why I have this snippet:

if (a.isSelected()) rb.setChecked(true);

But it is still happening. I’ve tried logging everything, debugging but I cant seem to get to the source of the problem. Maybe someone here has come across a similar problem.

Any help is appreciated,
Thank you in advance!

Answer 1

In the OnClick event, make sure that your reference to Question is the correct object. You might want to reference the question by the list index, because if you have two Questions on the screen at the same time, the reference of q could be the second question, but you have clicked the first questions answer.

** Added **
The issue is that q is a reference to a question, and each time through the instantiateItem function, this reference is set to a new instance of a question from the list. So when you execute the OnClick event, the value q might be pointing to the incorrect instance of question than what you expect. You would be better off getting the question out of the original list by the views index in the activity.

Something like the following:

public void onClick(View v) {
   RadioButton btn = (RadioButton) v;
   Question question = questionList.get(position);
   question.unselectAll(); // unselects all Answer's  
   question.getAnswer(btn.getId()).setSelected(true);
 }