Question

在由ddlPlant_SelectedIndexChanged引起的PostBack之后，我需要设置集HttpContext.Current.Session("PlantNumber")。这需要在ddlPlant在Site.Master中加载之后，但在Default.aspx中的代码需要该值之前发生。

Public Class SiteMaster Inherits MasterPage
    Protected Sub Page_Init(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Init
        If (Not Page.IsPostBack) Then
            ddlPlant.DataSource = myDataSource
            ddlPlant.DataBind()
            ddlPlant.SelectedValue = "1"
        End If

        HttpContext.Current.Session("PlantNumber") = ddlPlant.SelectedValue  
    End Sub

    Protected Sub ddlPlant_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs) Handles ddlPlant.SelectedIndexChanged
    End Sub
End Class


Public Class _Default Inherits Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
        Dim units As New List(Of EquipmentModel)
        For Each unit As EquipmentModel In getUnits.Out.Results
            If (CStr(unit.Plant_ID) = HttpContext.Current.Session("PlantNumber")) Then
                units.Add(unit)
            End If
        Next

        gvEquipmentUnit.DataSource = units.OrderBy(Function(n) n.Equipment_ID)
        gvEquipmentUnit.DataBind()
End Sub

使用上面的代码，在PostBack之后设置Session("PlantNumber")时，ddlPlant.SelectedIndex = Nothing，而ddlPlant.SelectedValue是一个空字符串。

我尝试将Session("PlantNumber") = ddlPlant.SelectedValue行转移到Site.Master的Page_Load，但是在之后运行在Default.aspx.vb中

Answer 1

我查了一下PreLoad，但显然它对Master页面不起作用。

最终，我决定不使用Session变量，而是直接从任何需要加载值的页面上调用控件（几乎所有这些）：

DirectCast(Master.FindControl("ddlPlant"), DropDownList).SelectedValue

在Page_Load

1 个答案: