C#编程-79：DataGridView分页显示

using System;
using System.Data;
using System.Data.SqlClient;
using System.Windows.Forms;
namespace DataGridViewDataNavigate
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        SqlDataAdapter sqladp;
        DataSet dateSet = new DataSet();
        private int startVal=0;//起始值
        private int perPageVal = 3;//每页显示数量
        private int totalVal;//总条数
        private int currentPage=0;//当前页
        private void Form1_Load(object sender, EventArgs e)
        {
            string constr = @"server=(localdb)\Projects;integrated security=sspi;database=company";
            SqlConnection sqlcon = new SqlConnection(constr);
            try
            {
                sqlcon.Open();
                string sql = "select * from clerk";
                sqladp = new SqlDataAdapter(sql,sqlcon);
                sqladp.Fill(dateSet,"clerk");
                //this.dataGridView1.DataSource = dateSet.Tables["clerk"];
                sqlcon.Close();
                //计算总页数
                totalVal = dateSet.Tables["clerk"].Rows.Count;
                int totalPage=(totalVal%perPageVal==0)?(totalVal/perPageVal):(totalVal/perPageVal+1);
                lblTotalPage.Text = "/" + totalPage;
                LoadData();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        private void LoadData()
        {
            //显示当前页面
            currentPage = startVal / perPageVal + 1;
            txtCurrentPage.Text = currentPage.ToString();
            //绑定数据
            dateSet.Clear();
            sqladp.Fill(dateSet, startVal, perPageVal, "clerk");
           bindingSource1.DataSource=dateSet.Tables[0];
           bindingNavigator1.BindingSource = bindingSource1;
           dataGridView1.DataSource = bindingSource1;
        }
        private void bindingNavigator1_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
        {
            if (e.ClickedItem.Text == "上一页")
            {
                startVal = startVal - perPageVal;
                if (startVal < 0)
                {
                    startVal = 0;
                    MessageBox.Show("已经是第一页");
                    return;
                }
            }
            if (e.ClickedItem.Text == "下一页")
            {
                startVal = startVal + perPageVal;
                if (startVal > totalVal)
                {
                    startVal = startVal - perPageVal;
                    MessageBox.Show("已经是最后一页");
                    return;
                }
            }
            LoadData();
        }
    }
}