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Listview分页,
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通过查询结果进行分页就是以结果集的子集处理查询结果的过程,这样,每次返回给用户的只是当前页面的数据大小。
DataAdapter对象通过重载Fill方法提供了返回当前页面数据的功能。然而,这种方法对大数据量的查询结果并不是最好的选择,这是因为:当DataAdapter用请求的结果填充DataTable或者DataSet时,数据库返回的资源仍是全部的查询结果,只是在返回时附加了额外的限定条件才返回了少量的记录集的。
要使用Fill方法返回当前一页的记录,需要指定开始记录startRecord,和当前页的最大记录数maxRecords。
下面的例子用来返回一页为5条记录的第一页的查询结果:
[VB.NET]
Dim currentIndex As Integer = 0
Dim pageSize As Integer = 5
Dim ordersql As String = "SELECT * FROM Orders ORDER BY OrderID"
Dim myDA As sqlDataAdapter = New sqlDataAdapter(ordersql,nwindConn)
Dim myDS As DataSet = New DataSet()
myDA.Fill(myDS,currentIndex,pageSize,"Orders")
[C#]
int currentIndex = 0;
int pageSize = 5;
string ordersql = "SELECT * FROM Orders ORDER BY OrderID";
sqlDataAdapter myDA = new sqlDataAdapter(ordersql,nwindConn);
DataSet myDS = new DataSet();
myDA.Fill(myDS,"Orders");
在上面的例子中,DataSet只填充了5条记录,但返回的仍是整个Orders表。如果要达到填充几条返回几天的目的,在sql语句中使用TOP和WHERE从句即可。例如:
[VB.NET]
Dim pageSize As Integer = 5
Dim ordersql As String = "SELECT TOP " & pageSize & " * FROM Orders ORDER BY OrderID"
Dim myDA As sqlDataAdapter = New sqlDataAdapter(ordersql,"Orders")
[C#]
int pageSize = 5;
string ordersql = "SELECT TOP " + pageSize + " * FROM Orders ORDER BY OrderID";
sqlDataAdapter myDA = new sqlDataAdapter(ordersql,"Orders");
此时需要注意的是:用这种方法进行的分页,必须自己维护记录排序的唯一标识,为了向下一页请求传递唯一的ID,我们必须象下面那样:
[VB.NET]
Dim lastRecord As String = myDS.Tables("Orders").Rows(pageSize - 1)("OrderID").ToString()
[C#]
string lastRecord = myDS.Tables["Orders"].Rows[pageSize - 1]["OrderID"].ToString();
下面的代码在Table填充之前进行了清空:
[VB.NET]
currentIndex = currentIndex + pageSize
myDS.Tables("Orders").Rows.Clear()
myDA.Fill(myDS,"Orders")
[C#]
currentIndex += pageSize;
myDS.Tables["Orders"].Rows.Clear();
myDA.Fill(myDS,"Orders");
下面是完整的代码:
[C#]
using System;
using System.Data;
using System.Data.sqlClient;
using System.Drawing;
using System.Windows.Forms;
public class PagingSample: Form
{
// Form 控件.
Button prevBtn = new Button();
Button nextBtn = new Button();
static DataGrid myGrid = new DataGrid();
static Label pageLbl = new Label();
// 分页变量
static int pageSize = 10; // 要显示的页数
static int totalPages = 0; // 总页数
static int currentPage = 0; // 当前页
static string firstVisibleCustomer = ""; // 当前页的第一条记录,用来进行移动“前一页”的定位。
static string lastVisibleCustomer = ""; //当前页的最后条记录,用来进行移动“下一页”的定位。
// DataSet用来绑定到DataGrid.
static DataTable custTable;
//初始化连接和DataAdapter.
static sqlConnection nwindConn = new sqlConnection("Data Source=.;Integrated Security=SSPI;Initial Catalog=northwind");
static sqlDataAdapter custDA = new sqlDataAdapter("",nwindConn);
static sqlCommand selCmd = custDA.SelectCommand;
public static void GetData(string direction)
{
// 创建返回一页记录的sql语句
selCmd.Parameters.Clear();
switch (direction)
{
case "下一页":
selCmd.CommandText = "SELECT TOP " + pageSize + " CustomerID,CompanyName FROM Customers " +
"WHERE CustomerID > @CustomerId ORDER BY CustomerID";
selCmd.Parameters.Add("@CustomerId",sqlDbType.VarChar,5).Value = lastVisibleCustomer;
break;
case "前一页":
selCmd.CommandText = "SELECT TOP " + pageSize + " CustomerID,CompanyName FROM Customers " +
"WHERE CustomerID < @CustomerId ORDER BY CustomerID DESC";
selCmd.Parameters.Add("@CustomerId",5).Value = firstVisibleCustomer;
break;
default:
selCmd.CommandText = "SELECT TOP " + pageSize + " CustomerID,CompanyName FROM Customers ORDER BY CustomerID";
// 计算总页数
sqlCommand totCMD = new sqlCommand("SELECT Count(*) FROM Customers",nwindConn);
nwindConn.Open();
int totalRecords = (int)totCMD.ExecuteScalar();
nwindConn.Close();
totalPages = (int)Math.Ceiling((double)totalRecords / pageSize);
break;
}
// 用查询结果填充临时表
DataTable tmpTable = new DataTable("Customers");
int recordsAffected = custDA.Fill(tmpTable);
// 如果表不存在,就创建
if (custTable == null)
custTable = tmpTable.Clone();
// 如果有记录返回,就刷新表
if (recordsAffected > 0)
{
switch (direction)
{
case "下一页":
currentPage++;
break;
case "上一页":
currentPage--;
break;
default:
currentPage = 1;
break;
}
pageLbl.Text = "第" + currentPage + "/ " + totalPages + "页";
// 清除行集,添加新记录
custTable.Rows.Clear();
foreach (DataRow myRow in tmpTable.Rows)
custTable.ImportRow(myRow);
// 保存first 和 last 关键值
DataRow[] ordRows = custTable.Select("","CustomerID ASC");
firstVisibleCustomer = ordRows[0][0].ToString();
lastVisibleCustomer = ordRows[custTable.Rows.Count - 1][0].ToString();
}
}
public PagingSample()
{
// 初始化控件并添加到Form
this.ClientSize = new Size(360,274);
this.Text = "NorthWind 数据表";
myGrid.Location = new Point(10,10);
myGrid.Size = new Size(340,220);
myGrid.AllowSorting = true;
myGrid.CaptionText = "NorthWind 客户信息";
myGrid.ReadOnly = true;
myGrid.AllowNavigation = false;
myGrid.PreferredColumnWidth = 150;
prevBtn.Text = "前一页";
prevBtn.Size = new Size(60,24);
prevBtn.Location = new Point(50,240);
prevBtn.Click += new EventHandler(Prev_OnClick);
nextBtn.Text = "下一页";
nextBtn.Size = new Size(60,24);
nextBtn.Location = new Point(120,240);
pageLbl.Text = "没有记录返回";
pageLbl.Size = new Size(130,16);
pageLbl.Location = new Point(200,244);
this.Controls.Add(myGrid);
this.Controls.Add(prevBtn);
this.Controls.Add(nextBtn);
this.Controls.Add(pageLbl);
nextBtn.Click += new EventHandler(Next_OnClick);
// 计算默认的第一页,并进行绑定
GetData("Default");
DataView custDV = new DataView(custTable,"","CustomerID",DataViewRowState.CurrentRows);
myGrid.SetDataBinding(custDV,"");
}
public static void Prev_OnClick(object sender,EventArgs args)
{
GetData("前一页");
}
public static void Next_OnClick(object sender,EventArgs args)
{
GetData("下一页");
}
}
public class Sample
{
static void Main()
{
Application.Run(new PagingSample());
}
}
原文链接:https://www.f2er.com/vb/262474.html