Question

我有一个奇怪的问题。

我有一个包含2个DropDownLists的页面和一个自定义的Web用户控件。自定义Web用户控件中有一个UpdatePanel，UpdatePanel中有一个Ajax Timer控件，用于定期更新内容列表。

当我“下拉”其中一个DropDownLists并将鼠标悬停在（而不是单击）一个选项时，UpdatePanel中的Timer控件异步回发到服务器，DropDownList“autopostbacks”到服务器！

我正在试图找出为什么异步回发会导致DropDownList就像我选择/点击某个选项一样，以便我可以找到解决此问题的方法。

现在再现这个问题非常简单。创建名为“TimerUpdatedListing”的Web用户控件...这是Web用户控件的ASPX代码标记：

<%@ Control Language="vb" AutoEventWireup="false" CodeBehind="TimerUpdatedListing.ascx.vb" Inherits="MyNamespace.TimerUpdatedListing" %>
<div style="width: 150px; height: 150px; overflow: auto; border: solid 1px navy;">
    <asp:UpdatePanel ID="anUpdatePanel" runat="server">
        <ContentTemplate>
            <asp:Repeater ID="aRepeater" runat="server">
                <ItemTemplate>
                    <div style="border-bottom: solid 1px #EEC900; margin: 3px; padding: 2px;">
                        Id:
                        <%#Eval("Id")%>
                        <br />
                        Time:
                        <%#Eval("Time")%>
                    </div>
                </ItemTemplate>
            </asp:Repeater>
            <asp:Timer ID="aTimer" runat="server" Interval="2000">
            </asp:Timer>
        </ContentTemplate>
    </asp:UpdatePanel>
</div>

这是Web用户控件的VB.NET服务器端代码：

Public Partial Class TimerUpdatedListing
    Inherits System.Web.UI.UserControl

    Private _aListOFThings As List(Of Things)

    Private Sub aTimer_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles aTimer.Tick
        If Session("_aListOfThings") Is Nothing Then
            _aListOFThings = New List(Of Things)
        Else
            _aListOFThings = CType(Session("_aListOfThings"), List(Of Things))
        End If

        If _aListOFThings.Count > 9 Then
            _aListOFThings = New List(Of Things)
        End If

        _aListOFThings.Add(New Things((_aListOFThings.Count + 1).ToString, Now.ToString("hh:mm:ss")))
        Session("_aListOfThings") = _aListOFThings
        aRepeater.DataSource = _aListOFThings
        aRepeater.DataBind()
    End Sub

    Private Class Things
        Private _time As String
        Private _id As String
        Public Property Time() As String
            Get
                Return _time
            End Get
            Set(ByVal value As String)
                _time = value
            End Set
        End Property
        Public Property ID() As String
            Get
                Return _id
            End Get
            Set(ByVal value As String)
                _id = value
            End Set
        End Property
        Public Sub New(ByVal id As String, ByVal time As String)
            _id = id
            _time = time
        End Sub
    End Class
End Class

现在，在名为WebForm1.aspx的ASPX页面中，添加2个DropDownLists和Web用户控件：

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="WebForm1.aspx.vb" Inherits="MyNamespace.WebForm1" %>

<%@ Register Src="TimerUpdatedListing.ascx" TagName="TimerUpdatedListing" TagPrefix="uc1" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Test</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:ScriptManager ID="ScriptManager1" runat="server">
        </asp:ScriptManager>
        <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true">
            <asp:ListItem Text="1" Value="1" />
            <asp:ListItem Text="2" Value="2" />
            <asp:ListItem Text="3" Value="3" />
            <asp:ListItem Text="4" Value="4" />
            <asp:ListItem Text="5" Value="5" />
        </asp:DropDownList>
        <asp:Label ID="selectedValue1" runat="server"></asp:Label>
        <br />
        <asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="true">
            <asp:ListItem Text="a" Value="a" />
            <asp:ListItem Text="b" Value="b" />
            <asp:ListItem Text="c" Value="c" />
            <asp:ListItem Text="d" Value="d" />
            <asp:ListItem Text="e" Value="e" />
        </asp:DropDownList>
        <asp:Label ID="selectedValue2" runat="server"></asp:Label>
        <br />
        <br />
        <uc1:TimerUpdatedListing ID="TimerUpdatedListing1" runat="server" />
    </div>
    </form>
</body>
</html>

以下是WebForm1.aspx页面的VB.NET服务器端代码：

Public Partial Class WebForm1
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If String.IsNullOrEmpty(Request.Params("ddl1")) = False Then
            selectedValue1.Text = Request.Params("ddl1")
        End If
        If String.IsNullOrEmpty(Request.Params("ddl2")) = False Then
            selectedValue2.Text = Request.Params("ddl2")
        End If
    End Sub

    Private Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList1.SelectedIndexChanged
        Response.Redirect(Request.Url.LocalPath + "?ddl1=" + DropDownList1.SelectedValue.ToString, True)
    End Sub

    Private Sub DropDownList2_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList2.SelectedIndexChanged
        Response.Redirect(Request.Url.LocalPath + "?ddl2=" + DropDownList2.SelectedValue.ToString, True)
    End Sub
End Class

谢谢，

-Frinny

Answer 1

以下是使用触发器触发更新面板的示例。将timer.tick事件作为触发器，看看会发生什么

http://www.asp.net/ajax/tutorials/understanding-asp-net-ajax-updatepanel-triggers

PS：我不认为计时器必须包含在更新面板中。我实际上是在代码隐藏中构建我的计时器，并将它们全部放在标记之外。

Answer 2

我尝试了两种不同的解决方案来解决这个问题。

我做的第一件事就是检查Request.Params（“__ EVENTTARGET”）以查看它是否与DropDownList匹配。如果它匹配，那么我将调用Response.Redirect（）方法。

例如：

Public Partial Class WebForm1
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If String.IsNullOrEmpty(Request.Params("ddl1")) = False Then
            selectedValue1.Text = Request.Params("ddl1")
        End If
        If String.IsNullOrEmpty(Request.Params("ddl2")) = False Then
            selectedValue2.Text = Request.Params("ddl2")
        End If
    End Sub

    Private Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList1.SelectedIndexChanged
        Dim ctrlNameThatCausedPostback As String = Request.Params("__EVENTTARGET")
        If String.IsNullOrEmpty(ctrlNameThatCausedPostback) = False AndAlso Page.FindControl(ctrlNameThatCausedPostback) Is DropDownList1 Then
            Response.Redirect(Request.Url.LocalPath + "?ddl1=" + DropDownList1.SelectedValue.ToString, True)
        End If
    End Sub

    Private Sub DropDownList2_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList2.SelectedIndexChanged
        Dim ctrlNameThatCausedPostback As String = Request.Params("__EVENTTARGET")
        If String.IsNullOrEmpty(ctrlNameThatCausedPostback) = False AndAlso Page.FindControl(ctrlNameThatCausedPostback) Is DropDownList2 Then
            Response.Redirect(Request.Url.LocalPath + "?ddl2=" + DropDownList2.SelectedValue.ToString, True)
        End If
    End Sub
End Class

我注意到这并不总是有效。有时我在DropDownList中选择了一个选项，并且由于计时器勾选和所选索引更改事件同时发生，因此不会发生重定向。

所以我采取的第二种方法是检查页面是否在异步回发到服务器。如果是，那么我知道正在发生计时器刻度事件，并且不应该发生重定向。

例如：

Public Partial Class WebForm1
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If String.IsNullOrEmpty(Request.Params("ddl1")) = False Then
            selectedValue1.Text = Request.Params("ddl1")
        End If
        If String.IsNullOrEmpty(Request.Params("ddl2")) = False Then
            selectedValue2.Text = Request.Params("ddl2")
        End If
    End Sub

    Private Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList1.SelectedIndexChanged
        If ScriptManager.GetCurrent(Me.Page).IsInAsyncPostBack = False Then
            Response.Redirect(Request.Url.LocalPath + "?ddl1=" + DropDownList1.SelectedValue.ToString, True)
        End If
    End Sub

    Private Sub DropDownList2_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList2.SelectedIndexChanged
        If ScriptManager.GetCurrent(Me.Page).IsInAsyncPostBack = False Then
            Response.Redirect(Request.Url.LocalPath + "?ddl2=" + DropDownList2.SelectedValue.ToString, True)
        End If
    End Sub
End Class

这有帮助，重定向正常发生的可能性比以前的方法更好;但是，它仍然不是100％。

-Frinny

DropDownList AutoPostback在发生异步回发时触发

2 个答案: