VB Web - DropDownList 无法保留选定的数据

Question

我正在创建一个新的 Web 应用程序，该应用程序通过下拉菜单从 SQL 列中获取数据，以在 SQL 查询中使用以在 GridView 中显示数据。

到目前为止，数据显示一切正常。但我一直无法在下拉菜单中保留我选择的数据。

每次我在选择随机选项后单击执行查询代码时，它都会自动默认为列表中的第一个选项。

这是供参考的代码，也许有人知道出了什么问题。

Imports Microsoft.VisualBasic
Imports System.IO
Imports System.Data
Imports System.Data.OleDb
Imports System.Data.SqlClient
Imports System.Configuration
Imports System.Drawing

Public Class WebForm1
Inherits System.Web.UI.Page
Public Div_Adapter As New OleDb.OleDbDataAdapter


Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load


    Call Inv_no()

End Sub

Public Sub Inv_no() 'Load Inv No data from SQL & place it in dropdown list

    Dim cmd As New SqlCommand("SELECT distinct [Inv No] from [SQLIOT].[dbo].[ZDIE_MAIN_HISTORY] order by [Inv No]", SQLCONN)
    cmd.Connection.Open()
    '-------------------
    Dim ddlValues As SqlDataReader
    ddlValues = cmd.ExecuteReader()

    Inv.DataSource = ddlValues
    Inv.DataValueField = "Inv No"
    Inv.DataTextField = "Inv No"
    Inv.DataBind()

    cmd.Connection.Close()

End Sub

Protected Sub exe_Click(ByVal sender As Object, ByVal e As EventArgs) Handles exe.Click

    Dim check1
    Dim cmd As New SqlCommand
    Dim dsGROUP As New DataSet()

    check1 = Inv.SelectedItem.ToString

    Dim strSelectCmd As String = "SELECT [Project No],[Inv No],[Description] ,[Entry Date], convert(varchar(10),[Date],121) " _
                                 & "as [Date], REPLACE(RIGHT('0' + LTRIM(RIGHT(CONVERT(VARCHAR, [Time], 131), 14)), 14), ':000', ' ') " _
                                 & "AS [Time],[Problem + Repair Details] ,[Status],[Remarks],[Location],[Measurement (OK/NG)]," _
                                 & "[Accumulative Stroke],[Preventive Stroke],[PIC],[Flag] FROM [SQLIOT].[dbo].[ZDIE_MAIN_HISTORY] where " _
                                 & "[Inv No] = '" & check1 & "' order by [Project No]"

    Dim da As New SqlDataAdapter(strSelectCmd, SQLCONN)

    cmd.Connection = SQLCONN

    SQLCONN.Open()
    da.Fill(dsGROUP, "Die_Records")

    Dim dvGroup As DataView = dsGROUP.Tables("Die_Records").DefaultView

    WebDieView.DataSource = dvGroup
    WebDieView.DataBind()

    SQLCONN.Close()

End Sub

Public Overrides Sub VerifyRenderingInServerForm(ByVal control As Control)

End Sub
End Class

Answer 1

问题出在您的页面加载事件中。每次页面加载时，您都在运行这个

Call Inv_no()

所以当您的点击事件触发时，它也会加载页面并重置下拉菜单

在你的页面加载中试试这个

If Not IsPostBack Then
    Call Inv_no()
End if

Answer 2

Dim sqlConnection1 As New SqlConnection("Data Source= ***;Initial Catalog=**;Integrated Security=SSPI;")//your connection string,or you can fetch from web config
        Dim cmd As New SqlCommand
        Dim reader As SqlDataReader

        cmd.CommandText = "SELECT distinct [Inv No] from [SQLIOT].[dbo].[ZDIE_MAIN_HISTORY] order by [Inv No]" //check once query retriving values or not

        cmd.Connection = sqlConnection1

        sqlConnection1.Open()
        reader = cmd.ExecuteReader()

        If reader.Read() Then
            ddl_Country.DataSource = reader
            ddl_Country.DataTextField = "Inv No"
            ddl_Country.DataValueField = "Inv No"

            ddl_Country.DataBind()

        End If    
       sqlConnection1.Close()