C#未将对象引用设置到对象的实例

Question

//串定位        public int IndexOf(SeqString s, int starpos)        {            SeqString sub = this.SubString(starpos, this.GetLength() - starpos);            if (sub.GetLength() < s.GetLength())            {                                MessageBox.Show("找不到需要的字符串!");                return -1;            }            int i, j, v;            i = 0; j = 0;            while (i < sub.GetLength() && j < s.GetLength())            {                if (sub.data[i] == s.data[j])                {                    i++;                    j++;                }                else                {                    i = i - j + 1;                    j = 0;                }            }            if (j == s.GetLength())                v = i - s.GetLength() + starpos;            else                v = -1;            return v;        }

Answer 1

入参SeqString s为空了。