安卓expandable list view的问题

Question

public class MainActivity extends Activity {

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

        ExpandableListAdapter adapter = new BaseExpandableListAdapter()
        {
            int[] logos = new int[]
            {
                R.drawable.ayomi1,
                R.drawable.ayomi2,
                R.drawable.ayomi3,
                R.drawable.ic_launcher
            };
            private String[] ayomiTypes = new String[]
                    {"A","B","C","D"};
            private String[][] ayomis = new String[][]
            {
                    {"1","2","3","4","4+"},
                    {"5","6","7","8","8+"},
                    {"9","10","11","1112"},
                    {"12"}
            };
            @Override
            public Object getChild(int groupPosition, int childPosition)
            {
                return ayomis[groupPosition][childPosition];
            }
            @Override
            public long getChildId( int groupPosition, int childPosition)
            {
                return childPosition;
            }
            @Override
            public int getChildrenCount(int groupPosition)
            {
                return ayomis.length;
            }
            private TextView getTextView()
            {
                AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
                        ViewGroup.LayoutParams.MATCH_PARENT, 64);
                TextView textView = new TextView(MainActivity.this);
                textView.setLayoutParams(lp);
                textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);
                textView.setPadding(36, 0, 0, 0);
                textView.setTextSize(20);
                return textView;
            }

            @Override
            public View getChildView(int groupPosition, int childPosition,
                    boolean isLastChild, View convertView, ViewGroup parent)
            {
                TextView textView = getTextView();
                textView.setText(getChild(groupPosition, childPosition)
                        .toString());
                return textView;
            }
            @Override
            public Object getGroup(int groupPosition)
            {
                return ayomiTypes[groupPosition];
            }
            @Override
            public int getGroupCount()
            {
                return ayomiTypes.length;
            }
            @Override
            public long getGroupId(int groupPosition)
            {
                return groupPosition;
            }
            @Override
            public View getGroupView(int groupPosition, boolean isExpanded,
                    View convertView, ViewGroup parent)
            {
                LinearLayout ll = new LinearLayout(MainActivity.this);
                ll.setOrientation(0);
                ImageView logo = new ImageView(MainActivity.this);
                logo.setImageResource(logos[groupPosition]);
                ll.addView(logo);
                TextView textView = getTextView();
                textView.setText(getGroup(groupPosition).toString());
                ll.addView(textView);
                return ll;
            }
            @Override
            public boolean isChildSelectable(int groupPosition,
                    int childPosition)
            {
                return true;
            }
            @Override
            public boolean hasStableIds()
            {
                return true;
            }
        };
        ExpandableListView expandListView = (ExpandableListView) findViewById
                (R.id.List1);
        expandListView.setAdapter(adapter);
    }


}

以上代码会显示四张图片，点开前三张都会有四个可选下拉项目，第四张打开后看到唯一一个项目后意外终止。

问题是:

1. 为什么代码中有五个项目却只能显示四个？
2. 为什么最后一个会意外退出？
3. 为什么重写方法后依然能自动填充listview的内容，隐式的过程是什么呢？（代码中并没有循环录入的语句）

thank you for help and advice.