还是查询的问题

[gltgl]

根据条件查询，我把查询输入条件和查询结果放在了一个页面上。可以有查询结果了，但是现在有个新问题：
在得到查询结果以后，如果我进行了翻页，然后在输入新条件，会有以下提示：
无效的 CurrentPageIndex 值。它必须大于等于 0 且小于 PageCount。
我该在什么地方设置，让CurrentPageIndex值在点击按钮的时候自动设置成1呢？
源代码：
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
If Not IsPostBack Then
SetVirtualItemCount()
End If
End Sub

Private Sub LinkButton1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles LinkButton1.Click
Response.Redirect("htmlpage1.htm")
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click


Dim strSQL As String
Dim Strbt = Trim(txtBT.Text)
Dim Strnr = Trim(txtNR.Text)

If Strnr = "" And Strbt = "" Then
strSQL = "select * from files order by id desc"
ElseIf Strbt = "" Then
strSQL = "select * from files where texts like '%" & Strnr & "%' order by id desc"
ElseIf Strnr = "" Then
strSQL = "select * from files where topic like '%" & Strbt & "%' order by id desc"
Else
strSQL = " select * from files where topic like '%" & Strbt & "%' and texts like '%" & Strnr & "%' order by id desc"
End If
Label5.Text = strSQL

SetVirtualItemCount()
DataFiller()

End Sub

Sub DataFiller()
'只要翻页，重新输入查询条件就会出错！
Dim StrConn As String = ConfigurationSettings.AppSettings("DataConn")
Dim objConn As New SqlConnection(StrConn)
objConn.Open()

Dim strSQL As String = Label5.Text

Dim objAdapter As New SqlDataAdapter(strSQL, objConn)

Dim objDataSet As New DataSet()
objAdapter.Fill(objDataSet, "topic")

MyGrid.DataSource = objDataSet.Tables.Item("topic")
MyGrid.DataBind()
End Sub

Sub GridPageChange(ByVal S As Object, ByVal E As DataGridPageChangedEventArgs)
MyGrid.CurrentPageIndex = E.NewPageIndex
DataFiller()
End Sub

Sub SetVirtualItemCount()
' Set up the connection
Dim strConn As String = ConfigurationSettings.AppSettings("DataConn")
Dim conn As New SqlConnection(strConn)

' Set up the command
Dim strCmd As String = "SELECT COUNT(*) FROM files"
Dim cmd As SqlCommand = New SqlCommand(strCmd, conn)

' Execute the command
conn.Open()
Dim nItemCount As Int32 = cmd.ExecuteScalar()
conn.Close()

MyGrid.VirtualItemCount = nItemCount
End Sub

[树猫]

设置 DataGrid的当前页索引 之前，先判断欲设置的索引是小于 DataGrid当前总页数-1，若是 将其设为1

[gltgl]

我添加了一句：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click


Dim strSQL As String
Dim Strbt = Trim(txtBT.Text)
Dim Strnr = Trim(txtNR.Text)

If Strnr = "" And Strbt = "" Then
strSQL = "select * from files order by id desc"
ElseIf Strbt = "" Then
strSQL = "select * from files where texts like '%" & Strnr & "%' order by id desc"
ElseIf Strnr = "" Then
strSQL = "select * from files where topic like '%" & Strbt & "%' order by id desc"
Else
strSQL = " select * from files where topic like '%" & Strbt & "%' and texts like '%" & Strnr & "%' order by id desc"
End If
Label5.Text = strSQL

mygrid.CurrentPageIndex=1
SetVirtualItemCount()
DataFiller()

End Sub