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using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
using System.Configuration;
namespace MyCommerce
{
 /// <summary>
 /// WebForm1 的摘要说明。
 /// </summary>
 public class WebForm1 : System.Web.UI.Page
 {
  protected System.Web.UI.WebControls.DataGrid DataGrid1;
  public enum GridNavigation:int
  {
   First = -2,
   Prevous = -1,
   Next = 1,
   Last=2
  }
  public GridNavigation Direction=GridNavigation.Next;

  private string queryStr_Pre="select * from (select top {0} * from  CMRC_Customers where CustomerID <  {1} order by CustomerID desc) as t order by CustomerID asc";
  protected System.Web.UI.WebControls.Button Btn_Pre;
  protected System.Web.UI.WebControls.Button Btn_Next;
  private string queryStr_Next="select top {0} * from CMRC_Customers where CustomerID > {1} ";
  private void Page_Load(object sender, System.EventArgs e)
  {
   // 在此处放置用户代码以初始化页面
   if(!Page.IsPostBack)
   {
    ViewState["FirstKey"]=0;
    ViewState["LastKey"]=0;
    SetVirtualPage();
    DataGrid1.CurrentPageIndex=0;
    DataGrid1_DataBind();
   }
  }

  private void DataGrid1_DataBind()
  {
   if(DataGrid1.CurrentPageIndex == 0)
   {
    Btn_Pre.Enabled=false;
   }
   else
   {
    Btn_Pre.Enabled=true;
   }
   if(DataGrid1.CurrentPageIndex == Convert.ToInt32(ViewState["TotalPage"]))
   {
    Btn_Next.Enabled=false;
   }
   else
   {
    Btn_Next.Enabled=true;
   }
  
   SqlDataReader dr=GetDataSource();
   DataGrid1.DataSource=dr;

   DataGrid1.DataBind();
   dr.Close();

   ViewState["FirstKey"]=DataGrid1.DataKeys[0];
   ViewState["LastKey"]=DataGrid1.DataKeys[DataGrid1.Items.Count-1];
  }

  private SqlDataReader GetDataSource()
  {
   
   string cmd_Text = "";
   switch(Direction)
   {
    case GridNavigation.Next:
    
     cmd_Text=string.Format(queryStr_Next,DataGrid1.PageSize,Convert.ToInt32(ViewState["LastKey"]));
     break;
    case GridNavigation.Prevous:
    
     cmd_Text=string.Format(queryStr_Pre,DataGrid1.PageSize,Convert.ToInt32(ViewState["FirstKey"]));
     break;
   }

   SqlDataReader dr = SqlHelper.GetDataSourceByPageIndex(cmd_Text);
   return dr;

  }
  private void SetVirtualPage()
  {
   SqlConnection cn=new SqlConnection(ConfigurationSettings.AppSettings["ConnectionString"].ToString());
   SqlCommand cmd=new SqlCommand("select count(*) from CMRC_Customers",cn);
   cn.Open();
   DataGrid1.VirtualItemCount=(int)cmd.ExecuteScalar();
   ViewState["TotalPage"]=(DataGrid1.VirtualItemCount / 10);
   cn.Close();
   return ;
  }

 

  #region Web 窗体设计器生成的代码
  override protected void OnInit(EventArgs e)
  {
   //
   // CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。
   //
   InitializeComponent();
   base.OnInit(e);
  }
  
  /// <summary>
  /// 设计器支持所需的方法 - 不要使用代码编辑器修改
  /// 此方法的内容。
  /// </summary>
  private void InitializeComponent()
  {   
   this.Btn_Pre.Click += new System.EventHandler(this.Btn_Pre_Click);
   this.Btn_Next.Click += new System.EventHandler(this.Btn_Next_Click);
   this.Load += new System.EventHandler(this.Page_Load);

  }
  #endregion

 

//  private void DataGrid1_ItemCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs e)
//  {
//   switch(e.CommandArgument.ToString())
//   {
//    case DataGrid.NextPageCommandArgument:Direction=GridNavigation.Next;break;
//    case DataGrid.PrevPageCommandArgument:Direction=GridNavigation.Prevous;break;
//
//   }
//  }

  

  private void Btn_Pre_Click(object sender, System.EventArgs e)
  {
   DataGrid1.CurrentPageIndex -= 1;
   Direction = GridNavigation.Prevous;
   DataGrid1_DataBind();
  }

  private void Btn_Next_Click(object sender, System.EventArgs e)
  {
   DataGrid1.CurrentPageIndex += 1;
   Direction = GridNavigation.Next;
   DataGrid1_DataBind();
  }

 }
}