无法在ASP.NET的Setter属性中将项添加到DropDownList

我试图将一个项目添加到Setter中的DropDownList,但添加的项目不会保留。

我已确认Viewstate已按此问题中的建议正确启用( Switched to ASP.NET 3.5, DropDownList doesn't remember dynamically added items )

这是我的密码。

    Private Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
        If ddlCountry.Items.Count < Country.GetList.Length Then
            ddlCountry.DataSource = Country.GetList()
            ddlCountry.DataBind()
            'At this point, there are correctly 231 items in ddlCountry.'
        End If
    End Sub

    Public WriteOnly Property Country() As String
        Set(ByVal Value As String)
            If ddlCountry.Items.FindByValue(Value.Country) Is Nothing Then
                Dim li As New ListItem(Value.Country, Value.Country)
                ddlCountry.Items.Insert(0, li)
                ddlCountry.SelectedIndex = ddlCountry.Items.IndexOf(li)
                'At this point, there are correctly 232 items in ddlCountry'
            Else
                ddlCountry.SelectedValue = Value.Country
            End If
        End Set
    End Property

    Private Sub Page_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
        If ddlCountry.Items.FindByText("<-- Please Select-->") Is Nothing Then
             'At this point, we are incorrectly'
             'back to 231 items - this is the problem.'
             ddlCountry.Items.Insert(0, New ListItem("<-- Please Select-->", ""))
        End If
    End Sub