IndexOutOfBoundsException in a BaseExpandableListAdapter implementing SectionIndexer

Question

I have created an alphabetical adapter, inspiring from this post with the adding of headers and for an expandableListView. Each group of my list have exactly one child.

Sometimes, and for reason that I don't understand, Android give me an IndexOutOfBoundsException with the getPositionForSection method. The section called is out of bound of the my sections string array. I think it's because of the expandable list but I'm not sure. Can you help me ?

public class AlphabeticalAdapter extends BaseExpandableListAdapter implements SectionIndexer{

private HashMap<String, Integer> alphaIndexer;
private String[] sections;
private HashMap<String, String> dictionnary;
private ArrayList<String> words;
private LayoutInflater inflater;

public AlphabeticalAdapter(Context context, HashMap<String, String> dictionnary){

    this.inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    this.dictionnary = dictionnary;
    this.words = new ArrayList<String>(this.dictionnary.keySet());
    Collections.sort(this.words, String.CASE_INSENSITIVE_ORDER);

    this.alphaIndexer = new HashMap<String, Integer>();
    for (int i = 0; i < this.words.size(); i++){
        String s = this.words.get(i).substring(0, 1).toUpperCase();
        if (!this.alphaIndexer.containsKey(s)){
            this.alphaIndexer.put(s, i);
        }
    }

    Set<String> sectionLetters = this.alphaIndexer.keySet();
    ArrayList<String> sectionList = new ArrayList<String>(sectionLetters);
    Collections.sort(sectionList);

    this.sections = new String[sectionList.size()];
    for (int i = 0; i < sectionList.size(); i++){
        this.sections[i] = sectionList.get(i);
    }

}

@Override
public int getSectionForPosition(int position){

    String currentFirstChar = this.words.get(position).substring(0, 1).toUpperCase();
    for (int section = 0; section < this.sections.length; section++){
        if (this.sections[section].equals(currentFirstChar)){
            return section;
        }
    }

    return 1;

}

@Override
public int getPositionForSection(int section){
    return this.alphaIndexer.get(this.sections[section]);   
}

@Override
public Object[] getSections(){
    return this.sections;
}

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

@Override
public Object getChild(int groupPosition, int childPosition) {
    return this.dictionnary.get(getGroup(groupPosition));
}

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

@Override
public int getChildrenCount(int groupPosition) {
    return 1;
}

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

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

@Override
public View getGroupView(int groupPosition, boolean isExpanded,
        View convertView, ViewGroup parent) {

    View view = (View) inflater.inflate(R.layout.glossary_word_row, null);

    TextView header = (TextView) view.findViewById(R.id.section);
    TextView rowText = (TextView) view.findViewById(R.id.textView);

    String currentWord = this.words.get(groupPosition);
    String currentFirstChar = currentWord.substring(0, 1).toUpperCase();

    rowText.setText(currentWord);

    if (groupPosition == this.alphaIndexer.get(currentFirstChar)){
        header.setVisibility(View.VISIBLE);
        header.setText(currentFirstChar);
    }

    return view;

}

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

    View view = (View) this.inflater.inflate(R.layout.glossary_word_row, null);
    TextView rowText = (TextView) view.findViewById(R.id.textView);
    rowText.setText(this.dictionnary.get(this.words.get(groupPosition)));

    return view;

}

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

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

}

Answer 1

I don't understand why this method is called with wrong parameter, but I have seen in the official Android documentation this :

Returns : the starting position of that section. If the section is out of bounds, the position must be clipped to fall within the size of the list.

So I have write this :

@Override
public int getPositionForSection(int section){
    if (section >= this.sections.length){
        return getGroupCount() - 1;
    }
    return this.alphaIndexer.get(this.sections[section]);   
}

And all is working well. Problem solved :-)