public string GetThisPage(PSVReaderUI.StreamPageLabel sampleLabel)
        {
            int index = 0;
            int lenth = 0;

            PrepareOnePage(sampleLabel, true, curIndex, out index, out lenth);

            sampleLabel.ContentIndex = index;
            sampleLabel.ContentLenth = lenth;

            return(str.Substring(index, lenth));
        }
        public string GetPrevPage(PSVReaderUI.StreamPageLabel sampleLabel)
        {
            if (false == HasPrev())
            {
                return(null);
            }

            int index = 0;
            int lenth = 0;

            PrepareOnePage(sampleLabel, false, curIndex, out index, out lenth);

            sampleLabel.ContentIndex = index;
            sampleLabel.ContentLenth = lenth;

            return(str.Substring(index, lenth));
        }