ExpandableListView 为什么小弟我的getChildView只执行一次

public class ListViewActivity extends Activity{    ExpandableListView expandableListView;    ListViewAdapter treeViewAdapter;    public String[] groups = { "2012-04-05", "2012-04-06", "2012-04-12"};    public String[][] child = { { "" }, { "" }, { "" } };    public void onCreate(Bundle savedInstanceState)    {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        treeViewAdapter = new ListViewAdapter(this,                ListViewAdapter.PaddingLeft >> 1);        expandableListView = (ExpandableListView) this        .findViewById(R.id.expandableListView);        List<ListViewAdapter.TreeNode> treeNode = treeViewAdapter.GetTreeNode();        for (int i = 0; i < groups.length; i++)        {            ListViewAdapter.TreeNode node = new ListViewAdapter.TreeNode();            node.parent = groups[i];            for (int ii = 0; ii < child[i].length; ii++)            {                node.childs.add(child[i][ii]);            }            treeNode.add(node);        }        treeViewAdapter.UpdateTreeNode(treeNode);        expandableListView.setAdapter(treeViewAdapter);    }    class MyGridView extends GridView    {        public MyGridView(android.content.Context context,                android.util.AttributeSet attrs)        {            super(context, attrs);        }        /**         * 设置不滚动         */        public void onMeasure(int widthMeasureSpec, int heightMeasureSpec)        {            int expandSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2,            MeasureSpec.AT_MOST);            super.onMeasure(widthMeasureSpec, expandSpec);        }    }}

public class ListViewAdapter extends BaseExpandableListAdapter implements        OnItemClickListener {    public static final int ItemHeight = 48;// 每项的高度    public static final int PaddingLeft = 36;// 每项的高度    private int myPaddingLeft = 0;     List<String> childlist;    private MyGridView toolbarGrid;    private List<List<String>> mtimage_array = new ArrayList<List<String>>();    private List<TreeNode> treeNodes = new ArrayList<TreeNode>();    private Context parentContext;    private LayoutInflater layoutInflater;    static public class TreeNode {        Object parent;        List<Object> childs = new ArrayList<Object>();    }    public ListViewAdapter(Context view, int myPaddingLeft) {        parentContext = view;        this.myPaddingLeft = myPaddingLeft;    }    public List<TreeNode> GetTreeNode() {        return treeNodes;    }    public void UpdateTreeNode(List<TreeNode> nodes) {        treeNodes = nodes;    }    public void RemoveAll() {        treeNodes.clear();    }    public Object getChild(int groupPosition, int childPosition) {        return treeNodes.get(groupPosition).childs.get(childPosition);    }    public int getChildrenCount(int groupPosition) {        return treeNodes.get(groupPosition).childs.size();    }    static public TextView getTextView(Context context) {        AbsListView.LayoutParams lp = new AbsListView.LayoutParams(                ViewGroup.LayoutParams.FILL_PARENT, ItemHeight);        TextView textView = new TextView(context);        textView.setLayoutParams(lp);        textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);        return textView;    }    /**     * 可自定义ExpandableListView     */    public View getChildView(int groupPosition, int childPosition,            boolean isLastChild, View convertView, ViewGroup parent) {        getPictures("/mnt/sdcard/photoimages");        if (convertView == null) {            layoutInflater = (LayoutInflater) parentContext                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);            convertView = layoutInflater.inflate(R.layout.view, null);            toolbarGrid = (MyGridView) convertView                    .findViewById(R.id.GridView_toolbar);            toolbarGrid.setNumColumns(4);// 设置每行列数            toolbarGrid.setGravity(Gravity.CENTER);// 位置居中            toolbarGrid.setHorizontalSpacing(10);// 水平间隔            toolbarGrid.setAdapter(getMenuAdapter(getChildpicture(groupPosition)));// 设置菜单Adapter            toolbarGrid.setOnItemClickListener(this);                    }        return convertView;    }    /**     * 可自定义list     */    public View getGroupView(int groupPosition, boolean isExpanded,            View convertView, ViewGroup parent) {        TextView textView = getTextView(this.parentContext);        textView.setText(getGroup(groupPosition).toString());        textView.setPadding(myPaddingLeft + PaddingLeft, 0, 0, 0);        return textView;    }    public long getChildId(int groupPosition, int childPosition) {        return childPosition;    }    public Object getGroup(int groupPosition) {        return treeNodes.get(groupPosition).parent;    }    public int getGroupCount() {        return treeNodes.size();    }    public long getGroupId(int groupPosition) {        return groupPosition;    }    public boolean isChildSelectable(int groupPosition, int childPosition) {        return true;    }    public boolean hasStableIds() {        return true;    }    /**     * 构造菜单Adapter     *      * @param menuNameArray     *            名称     * @param mtimage_array2     *            图片     * @return SimpleAdapter     */    private SimpleAdapter getMenuAdapter(List<String> mtimage_array2) {        ArrayList<HashMap<String, Object>> data = new ArrayList<HashMap<String, Object>>();        for (int i = 0; i < mtimage_array2.size(); i++) {            HashMap<String, Object> map = new HashMap<String, Object>();            map.put("itemImage", mtimage_array2.get(i));            data.add(map);        }        SimpleAdapter simperAdapter = new SimpleAdapter(parentContext, data,                R.layout.item_menu, new String[] { "itemImage" },                new int[] { R.id.item_image });        childlist.clear();        return simperAdapter;    }    @Override    public void onItemClick(AdapterView<?> parent, View view, int position,            long id) {        Toast.makeText(parentContext, "当前选中的是:" + position, Toast.LENGTH_SHORT)                .show();    }    /*public void ishavedatatime( List <String> listdata)    {        for(int i=0;i<mtimage_array.size();i++)        {            if(mtimage_array.get(i).get(0)==listdata.get(0))            {                mtimage_array.get(i).add(listdata.get(1));                break;            }                    }        mtimage_array.add(listdata);                    }*/     public  void getPictures(String itemcs) {                                        File file = new File(itemcs);              File[] files = file.listFiles();                      for(int i = 0; i < files.length; i++) {                  final File f = files[i];                                if(f.isFile()) {                      try{                          int idx = f.getPath().lastIndexOf(".");                          if (idx <= 0) {                              continue;                          }                          String suffix = f.getPath().substring(idx);                          if (suffix.toLowerCase().equals(".jpg") ||                              suffix.toLowerCase().equals(".jpeg") ||                              suffix.toLowerCase().equals(".bmp") ||                              suffix.toLowerCase().equals(".png") ||                              suffix.toLowerCase().equals(".gif") )                          {                              List <String> lists =new ArrayList<String>();                            String datatime=f.getName().substring(0,10);                            String path=f.getPath();                            lists.add(datatime);                            lists.add(path);                            mtimage_array.add(lists);                            lists=null;                                                    }                      } catch(Exception e) {                          e.printStackTrace();                      }                  }              }                  }     public List<String> getChildpicture(int grouppos)     {         ListViewActivity li=new ListViewActivity();          childlist=new ArrayList<String>();        String jj=li.groups[grouppos];                  for(int i=0;i<mtimage_array.size();i++)         {             String cc=mtimage_array.get(i).get(0).toString();             if(jj.equals(cc))             {                 childlist.add(mtimage_array.get(i).get(1));             }         }         return childlist;              }     }