每个回发下拉列表项重复之后 [英] After every postback dropdownlist items repeats

问题描述

我已将下拉列表与数据库绑定。但是在每个PostBack上，下拉列表中的项目都会再次重复。

I have bind my dropdownlist with database. But on each PostBack the items in dropdownlist gets repeat again.

例如
OnPage Load我在下拉列表1,2,3,4中有此项目。等等现在假设页面被postBack然后看起来像1,2,3,4,1,2,3,4

e.g. OnPage Load I have this items in dropdownlist 1,2,3,4.. etc Now suppose page gets postBack then it looks like 1,2,3,4,1,2,3,4

Vb代码

Private Sub hospitals_Load(sender As Object, e As EventArgs) Handles Me.Load
Me.PopulateAreas()
End Sub


Private Sub PopulateAreas()
        If IsPostBack Then
            Dim citySelector As DropDownList = Page.Master.FindControl("locationSelector")
            Using conn As New MySqlConnection()
                conn.ConnectionString = ConfigurationManager _
                    .ConnectionStrings("conio").ConnectionString()
                Using cmd As New MySqlCommand()
                    cmd.CommandText = "Select * from areas where areaCity Like '" + citySelector.SelectedItem.ToString + "%'"
                    cmd.Connection = conn
                    conn.Open()
                    Using sdr As MySqlDataReader = cmd.ExecuteReader()
                        While sdr.Read()
                            Dim item As New ListItem()
                            item.Text = sdr("areaName").ToString()
                            item.Value = sdr("areaID").ToString()
                            'item.Selected = Convert.ToBoolean(sdr("IsSelected"))
                            areasList.Items.Add(item)
                        End While
                    End Using
                    conn.Close()
                End Using
            End Using
        End If

更新

我有一个主页，其中包含城市的下拉列表。我正在使用mypage控件对mycontent页面进行如下操作。

I have master page which has dropdownlist of cities. I am using masterpage control to mycontent page like below.

Dim citySelector As DropDownList = Page.Master.FindControl("locationSelector")

现在在我的PopulateArea（）类中，存在一个查询，其中WHERE子句具有cityselector。

Now in my PopulateArea() class there is query in which WHERE clause have cityselector. So according to city my area gets fetched.

推荐答案

将您的代码更改为

Private Sub PopulateAreas()
    If IsPostBack Then
        areasList.Items.clear()
        Dim citySelector As DropDownList = Page.Master.FindControl("locationSelector")
        Using conn As New MySqlConnection()
            conn.ConnectionString = ConfigurationManager _
                .ConnectionStrings("conio").ConnectionString()
            Using cmd As New MySqlCommand()
                cmd.CommandText = "Select * from areas where areaCity Like '" + citySelector.SelectedItem.ToString + "%'"
                cmd.Connection = conn
                conn.Open()
                Using sdr As MySqlDataReader = cmd.ExecuteReader()
                    While sdr.Read()
                        Dim item As New ListItem()
                        item.Text = sdr("areaName").ToString()
                        item.Value = sdr("areaID").ToString()
                        'item.Selected = Convert.ToBoolean(sdr("IsSelected"))
                        areasList.Items.Add(item)
                    End While
                End Using
                conn.Close()
            End Using
        End Using
    End If
End Sub

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