Question

我正在学习ASP.Net开发＆amp;尝试创建Web应用程序，其中ListView数据应该在ComboBox中完成筛选器选择。我制作了ListView＆amp;将它绑定到我的数据库表＆amp;试图把ComboBox过滤器但是得到这个错误

输出中的
（System.Web.HttpException：请求在此上下文中不可用）。

VB代码

Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Partial Class VB
    Inherits System.Web.UI.Page
    Dim query As String
    Dim strArea As String = Request.QueryString("Country")

    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
        If Not Me.IsPostBack Then
            Me.BindListView()
        End If
    End Sub

    Private Sub BindListView()
        Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Using con As New SqlConnection(constr)
            Using cmd As New SqlCommand()
                cmd.CommandText = "SELECT CustomerId, ContactName, Country FROM Customers"
                cmd.Connection = con
                Using sda As New SqlDataAdapter(cmd)
                    Dim dt As New DataTable()
                    sda.Fill(dt)
                    lvCustomers.DataSource = dt
                    lvCustomers.DataBind()
                End Using
            End Using
        End Using
    End Sub

    Protected Sub OnPagePropertiesChanging(sender As Object, e As PagePropertiesChangingEventArgs)
        TryCast(lvCustomers.FindControl("DataPager1"), DataPager).SetPageProperties(e.StartRowIndex, e.MaximumRows, False)
        Me.BindListView()
    End Sub

    Protected Sub country_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles country.SelectedIndexChanged
        Try
            If country.SelectedValue <> "All" Then
                query = "Select CutomerId, Contact Name, Country from Customers where Country like '%" + strArea + "%' order by rank;"
            End If
            Dim cmd As New SqlCommand(query)
            Dim da As New SqlDataAdapter(cmd)
            Dim table As New DataTable
        Catch ex As Exception

        End Try

    End Sub
End Class

Answer 1

Request只读属性属于Page类，并且继承的类成员仅在继承它的类的成员中可用（在您的情况下为VB）。像这样更改你的代码： -

Partial Class VB
    Inherits System.Web.UI.Page
    Dim query As String
    Dim strArea As String = String.Empty

    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
        If Not Me.IsPostBack Then
            Me.BindListView()
        End If
        strArea  = Request.QueryString("Country")
    End Sub

另外，请注意最好在分配之前检查查询字符串变量中是否存在任何值。

通过选择ComboBox来过滤listview数据

1 个答案: