my code review

class ListDeviceAdapter extends BaseAdapter  
    {  
        ChildListView childlist = null;  
        private Context mContext;  
        private List<Map<String, Object>> mDeviceData; // 设备信息集合  
  
        public ListDeviceAdapter(Context context, List<Map<String, Object>> listItems)  
        {  
            this.mContext = context;  
            this.mDeviceData = listItems;  
            System.out.println("-- ListDeviceAdapter is running...--");  
        }  
  
        @Override  
        public int getCount()  
        {  
            return 0;//return mDeviceData.size();//首先回调getCount()方法，根据其值来决定是否回调getView()  
        }  
  
        @Override  
        public Object getItem(int position)  
        {  
            return mDeviceData.get(position);  
        }  
  
        @Override  
        public long getItemId(int position)  
        {  
            return 0;  
        }  
  
        @Override  
        public View getView(int position, View convertView, ViewGroup parent)  
        {  
            System.out.println("-- getView is running...--");  
            if (convertView == null)  
            {  
                System.out.println("-- list is running...--");  
                childlist = new ChildListView();  
                convertView = LayoutInflater.from(mContext).inflate(R.layout.listview_control, null);  
                childlist.mDeviceType = (ImageButton) convertView.findViewById(R.id.list_btn_device_type);  
                childlist.mDeviceName = (TextView) convertView.findViewById(R.id.list_text_device_name);  
                childlist.mDeviceControl = (ImageButton) convertView.findViewById(R.id.list_btn_device_type);  
                convertView.setTag(childlist);  
            } else  
            {  
                childlist = (ChildListView) convertView.getTag();  
            }  
  
            childlist.mDeviceType.setBackgroundResource(R.drawable.device_light);  
            childlist.mDeviceName.setText(mDeviceData.get(0).get("title").toString());  
            childlist.mDeviceControl.setBackgroundResource(R.drawable.device_curtain);  
  
            childlist.mDeviceType.setOnClickListener(new OnClickListener()  
            {  
                public void onClick(View v)  
                {  
  
                }  
            });  
            childlist.mDeviceControl.setOnClickListener(new OnClickListener()  
            {  
                public void onClick(View v)  
                {  
  
                }  
            });  
  
            return convertView;  
        }  
  
        class ChildListView  
        {  
            ImageButton mDeviceType;  
            TextView mDeviceName;  
            ImageButton mDeviceControl;  
        }  
    }  

 发现自定义Adapter先是回调的getCount()方法，起初返回的是空