ASP.net 网站中的导航错误

Question

我使用 Visual Studio 2008 开发了一个网站。它使用活动索引从一个页面导航到下一页。

当用户单击下一步按钮时，它将增加索引。根据增加的值，已导航下一页。

第一页中有一个下拉菜单，其值为（A，B，C，D）。

通常，网站按以下方式导航：

Page1-->page2-->Page1-->page2-->Page1-->page2--> Page3-->Page4 依此类推。

但是，如果 Page1 中的下拉框中的值为“B”，则会导致以下流程。

Page1-->page2-->Page4

但问题是......网站表现得很奇怪。它给出以下流程..

对于下拉选择中的特定值选择（值“B”），Page1-->page2-->Page3-->Page4 而不是 Page1-->page2-->Page4 。

当用户再次转到最后一页时，使用后退按钮回到前面并使用“下一页”按钮转到最后一页，就会发生此问题。 （多次迭代导致此问题）

我在这里需要两件事：

1. 为什么会发生？
2. 如何防止这种情况

我已经给出了下面的代码：

感谢您提前的帮助，

Protected Sub btn_view1_back_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btn_view1_back.Click, btn_view2_back.Click, btn_view3_back.Click
      Try
          Dim currentView As Int16
          currentView = mvRequestorForm.ActiveViewIndex
          If currentView = 3 And BSelected() = 1 Then
              mvRequestorForm.ActiveViewIndex = (currentView - 2)
          Else
              mvRequestorForm.ActiveViewIndex = (currentView - 1)
          End If

          If mvRequestorForm.ActiveViewIndex = 1 Then
              If (ddl_view0_WULValue() = 0) Then
                  'C'
                  CSelected() = 1
                  strRoleType = "chkBx_C_workunit"
              ElseIf (ddl_view0_WULValue() = 1) Then
                  'head office'
                  ASelected() = 1
                  strRoleType = "chkBx_A_workunit"
              ElseIf (ddl_view0_WULValue() = 2) Then
                  'B'
                  BSelected() = 1
                  strRoleType = "chkBx_B_workunit"
              ElseIf (ddl_view0_WULValue() = 3) Then
                  'B'
                  BSelected() = 1
                  strRoleType = "chkBx_B_workunit"
              End If
          End If

      Catch ex As Exception

      End Try
End Sub

下面的“下一步”按钮代码：

Protected Sub btn_View0_Next_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btn_View0_Next.Click, btn_View1_Next.Click, btn_view2_Next.Click

    Try
        Dim currentView As Int16
        currentView = mvRequestorForm.ActiveViewIndex
        If currentView = 1 And BSelected = 1 Then
            mvRequestorForm.ActiveViewIndex = (currentView + 2)
            rfv_view2_managersEmail.Enabled = True
            rev_view2_managersEmail.Enabled = True
        Else
            mvRequestorForm.ActiveViewIndex = (currentView + 1)
        End If

        If mvRequestorForm.ActiveViewIndex = 1 Then
            Sub_ActivateView1()
        End If

    Catch ex As Exception

    End Try
End Sub

Answer 1

如果您发布 ASelected()、BSelected()、CSelected() 和 ddl_view0_WULValue() 会有更多帮助。如果没有它，我无法真正确定为什么会发生这种情况。我的猜测是因为 Web 应用程序中缺乏状态。当您尝试在页面的代码隐藏中设置变量时，对象仅在该单个回发期间（在本例中为单击按钮）保留在周围。下次单击按钮时，页面私有变量的所有数据都将消失。

但是，下拉列表的状态将在回发之间保持，因此您可以直接查询下拉列表以了解已选择的内容。我将其更改为 ddl_view0.SelectedValue = "B"，而不是 BSelected() = 1

我认为这就是您的 aspx 页面的样子。请注意 ListItem 上 Text 和 Value 属性的使用。我们将使用代码中的 Value 属性来查找所选内容。

<asp:MultiView runat="server" ID="mvRequestorForm" ActiveViewIndex="0"
    <asp:View ID="View1" runat="server">
        1
        <asp:DropDownList ID="ddl_view0" runat="server">
            <asp:ListItem Text="Item A" Value="A"></asp:ListItem>
            <asp:ListItem Text="Item B" Value="B"></asp:ListItem>
            <asp:ListItem Text="Item C" Value="C"></asp:ListItem>
            <asp:ListItem Text="Item D" Value="D"></asp:ListItem>
        </asp:DropDownList>
        <asp:Button ID="btn_View0_Next" runat="server" Text="Next" />
    </asp:View>
    <asp:View ID="View2" runat="server">
        2
        <asp:Button ID="btn_View1_Next" runat="server" Text="Next" />
        <asp:Button ID="btn_view1_back" runat="server" Text="Back" />
    </asp:View>
    <asp:View ID="View3" runat="server">
        3
        <asp:Button ID="btn_view2_Next" runat="server" Text="Next" />
        <asp:Button ID="btn_view2_back" runat="server" Text="Back" />
    </asp:View>
    <asp:View ID="View4" runat="server">
        4
        <asp:Button ID="btn_view3_back" runat="server" Text="Back" />
    </asp:View>
</asp:MultiView>

我更改了您的代码以消除所有 ASelected()、BSelected、CSelected 和 dll_view0_WULValue() 调用，而直接使用下拉列表。

Protected Sub btn_view1_back_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btn_view1_back.Click, btn_view2_back.Click, btn_view3_back.Click
    'Try'

    If mvRequestorForm.ActiveViewIndex = 3 And ddl_view0.SelectedValue = "B" Then 'CHANGED to use the SelectedValue property of the dropdownlist because it keeps state properly'
        mvRequestorForm.ActiveViewIndex -= 2 'CHANGED to a cleaner way to decrement by 2'
    Else
        mvRequestorForm.ActiveViewIndex -= 1 'CHANGED to a cleaner way to decrement by 1'
    End If

    If mvRequestorForm.ActiveViewIndex = 1 Then 'NOTE: This is now at least one less than when the method started. Is this what you really wanted?'

        If (ddl_view0.SelectedValue = "C") Then 'CHANGED to use the SelectedValue property of the dropdownlist because it keeps state properly'
            strRoleType = "chkBx_C_workunit"

        ElseIf (ddl_view0.SelectedValue = "A") Then 'CHANGED to use the SelectedValue property of the dropdownlist because it keeps state properly'
            strRoleType = "chkBx_A_workunit"

        ElseIf (ddl_view0.SelectedValue = "B") Then 'CHANGED to use the SelectedValue property of the dropdownlist because it keeps state properly'
            strRoleType = "chkBx_B_workunit"

        End If
        'NOTE: There seemed to be a duplicate case for "B" here, so I removed it'

    End If
    'Catch ex As Exception'
    'Commented out Try/Catch because empty catches hide bugs and make development harder'
    'End Try'
End Sub

Protected Sub btn_View0_Next_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btn_View0_Next.Click, btn_View1_Next.Click, btn_view2_Next.Click
    'Try'
    If mvRequestorForm.ActiveViewIndex = 1 And ddl_view0.SelectedValue = "B" Then
        mvRequestorForm.ActiveViewIndex += 2 'CHANGED to a cleaner way to increment by 2'
        rfv_view2_managersEmail.Enabled = True
        rev_view2_managersEmail.Enabled = True
    Else
        mvRequestorForm.ActiveViewIndex += 1 'CHANGED to a cleaner way to increment by 1'
    End If

    If mvRequestorForm.ActiveViewIndex = 1 Then 'NOTE: This is now at least one more than when the method started. Is this what you really wanted?'
        'Sub_ActivateView1()'
    End If
    'Catch ex As Exception'
    'Commented out Try/Catch because empty catches hide bugs and make development harder'
    'End Try'
End Sub

我不知道 strRoleType 的用途，但这可能也无法正常工作。如果没有，请尝试在窗体上放置一个 HiddenField 控件并使用它来存储值。