View的setTag和getTag方法

public View getView(int position, View convertView, ViewGroup parent) {
        Msg msg =getItem(position);
        View view;
        ViewHolder viewHolder;
        if(convertView==null){
            view=LayoutInflater.from(getContext()).inflate(resourceId, null);
            viewHolder = new ViewHolder();
            viewHolder.leftLayout=(LinearLayout)view.findViewById(R.id.left_layout);
            viewHolder.rigthLayout=(LinearLayout)view.findViewById(R.id.right_layout);
            viewHolder.leftMsg=(TextView)view.findViewById(R.id.left_msg);
            viewHolder.rigthMsg=(TextView)view.findViewById(R.id.right_msg);
            view.setTag(viewHolder);
        }
        else{
            view=convertView;
            viewHolder=(ViewHolder)view.getTag();
        }
        if(msg.getType()==Msg.TYPE_RECEIVED){
            viewHolder.leftLayout.setVisibility(View.VISIBLE);
            viewHolder.rigthLayout.setVisibility(View.GONE);
            viewHolder.leftMsg.setText(msg.getContent());
        }else if(msg.getType()==Msg.TYPE_SENT){
            viewHolder.leftLayout.setVisibility(View.GONE);
            viewHolder.rigthLayout.setVisibility(View.VISIBLE);
            viewHolder.rigthMsg.setText(msg.getContent());
        }
        return view ;
    }
    
    class ViewHolder{
        LinearLayout leftLayout;
        LinearLayout rigthLayout;
        TextView leftMsg;
        TextView rigthMsg;
    }