添加新行后GridView中DropDownList重置：如何保留状态并刷新NoTagging

问题根源 #

• 启用AutoPostBack="True"后，下拉框选值触发回发，但未将ddlItem的选中值保存到ViewState的CurrentTable中
• SetPreviousData方法仅恢复了ddlNoTagging的选中状态，完全忽略ddlItem的状态恢复
• GridView重新绑定时，ddlItem通过SqlDataSource重新加载数据，但未从保存的状态中恢复选中值

解决方案 #

1. 扩展ViewState的DataTable，保存下拉框选中值 #

修改SetInitialRow方法，新增列存储两个下拉框的选中值：

Private Sub SetInitialRow()
    Dim dt As DataTable = New DataTable()
    dt.Columns.Add(New DataColumn("RowNumber", GetType(String)))
    dt.Columns.Add(New DataColumn("SelectedKodItem", GetType(String))) ' 存储ddlItem选中值
    dt.Columns.Add(New DataColumn("SelectedNoTagging", GetType(String))) ' 存储ddlNoTagging选中值

    Dim dr As DataRow = dt.NewRow()
    dr("RowNumber") = 1
    dr("SelectedKodItem") = String.Empty
    dr("SelectedNoTagging") = String.Empty
    dt.Rows.Add(dr)

    ViewState("CurrentTable") = dt
    Gridview1.DataSource = dt
    Gridview1.DataBind()

    Dim ddl1 As DropDownList = CType(Gridview1.Rows(0).Cells(1).FindControl("ddlItem"), DropDownList)
    Dim ddl2 As DropDownList = CType(Gridview1.Rows(0).Cells(2).FindControl("ddlNoTagging"), DropDownList)
    ' 无需手动填充，依赖SqlDataSource自动加载数据
End Sub

2. 下拉框选值变化时，保存状态到ViewState #

修改ddlItem_SelectedIndexChanged方法，同步更新ViewState中的选中值：

Protected Sub ddlItem_SelectedIndexChanged(sender As Object, e As EventArgs)
    Dim ddlItem As DropDownList = CType(sender, DropDownList)
    Dim row As GridViewRow = CType(ddlItem.NamingContainer, GridViewRow)
    Dim ddlNoTagging As DropDownList = CType(row.FindControl("ddlNoTagging"), DropDownList)

    ' 保存ddlItem选中值到ViewState
    If ViewState("CurrentTable") IsNot Nothing Then
        Dim dt As DataTable = CType(ViewState("CurrentTable"), DataTable)
        dt.Rows(row.RowIndex)("SelectedKodItem") = ddlItem.SelectedValue
        ViewState("CurrentTable") = dt
    End If

    ' 保留原有的ddlNoTagging刷新逻辑
    Dim sqlListTagging As SqlDataSource = CType(row.FindControl("sqlListTagging"), SqlDataSource)
    sqlListTagging.SelectParameters("KodItem").DefaultValue = ddlItem.SelectedValue
    ddlNoTagging.DataBind()
End Sub

3. 完善状态恢复逻辑，同时恢复两个下拉框 #

修改SetPreviousData方法，同时恢复ddlItem和ddlNoTagging的选中状态：

Private Sub SetPreviousData()
    Dim rowIndex As Integer = 0

    If ViewState("CurrentTable") IsNot Nothing Then
        Dim dt As DataTable = CType(ViewState("CurrentTable"), DataTable)

        If dt.Rows.Count > 0 Then
            For i As Integer = 0 To dt.Rows.Count - 1
                Dim ddl1 As DropDownList = CType(Gridview1.Rows(rowIndex).Cells(1).FindControl("ddlItem"), DropDownList)
                Dim ddl2 As DropDownList = CType(Gridview1.Rows(rowIndex).Cells(2).FindControl("ddlNoTagging"), DropDownList)

                If ddl1 IsNot Nothing AndAlso ddl2 IsNot Nothing Then
                    ' 恢复ddlItem选中值
                    Dim savedKodItem As String = dt.Rows(i)("SelectedKodItem").ToString()
                    If Not String.IsNullOrEmpty(savedKodItem) Then
                        Dim itemToSelect As ListItem = ddl1.Items.FindByValue(savedKodItem)
                        If itemToSelect IsNot Nothing Then
                            itemToSelect.Selected = True
                            ' 联动刷新ddlNoTagging并恢复其选中值
                            Dim sqlListTagging As SqlDataSource = CType(Gridview1.Rows(rowIndex).Cells(2).FindControl("sqlListTagging"), SqlDataSource)
                            sqlListTagging.SelectParameters("KodItem").DefaultValue = savedKodItem
                            ddl2.DataBind()

                            Dim savedNoTagging As String = dt.Rows(i)("SelectedNoTagging").ToString()
                            If Not String.IsNullOrEmpty(savedNoTagging) Then
                                Dim taggingItem As ListItem = ddl2.Items.FindByValue(savedNoTagging)
                                If taggingItem IsNot Nothing Then
                                    taggingItem.Selected = True
                                End If
                            End If
                        End If
                    End If
                End If
                rowIndex += 1
            Next
        End If
    End If
End Sub

4. 新增行时维护空状态值 #

修改AddNewRowToGrid方法，确保新增行的状态列有初始值：

Private Sub AddNewRowToGrid()
    If ViewState("CurrentTable") IsNot Nothing Then
        Dim dtCurrentTable As DataTable = CType(ViewState("CurrentTable"), DataTable)
        Dim drCurrentRow As DataRow = dtCurrentTable.NewRow()

        drCurrentRow("RowNumber") = dtCurrentTable.Rows.Count + 1
        drCurrentRow("SelectedKodItem") = String.Empty
        drCurrentRow("SelectedNoTagging") = String.Empty
        dtCurrentTable.Rows.Add(drCurrentRow)
        ViewState("CurrentTable") = dtCurrentTable

        Gridview1.DataSource = dtCurrentTable
        Gridview1.DataBind()
    Else
        Response.Write("ViewState is null")
    End If

    SetPreviousData()
End Sub

5. 可选：保存ddlNoTagging的选中状态 #

如果需要持久化ddlNoTagging的选中值，添加事件处理：

Protected Sub ddlNoTagging_SelectedIndexChanged(sender As Object, e As EventArgs)
    Dim ddlNoTagging As DropDownList = CType(sender, DropDownList)
    Dim row As GridViewRow = CType(ddlNoTagging.NamingContainer, GridViewRow)

    If ViewState("CurrentTable") IsNot Nothing Then
        Dim dt As DataTable = CType(ViewState("CurrentTable"), DataTable)
        dt.Rows(row.RowIndex)("SelectedNoTagging") = ddlNoTagging.SelectedValue
        ViewState("CurrentTable") = dt
    End If
End Sub

同时在前端给ddlNoTagging添加事件属性：

<asp:DropDownList ID="ddlNoTagging" runat="server"
                  AppendDataBoundItems="True" class="form-control" 
                  DataSourceID="sqlListTagging" DataTextField="NoTagging" 
                  DataValueField="IDItem" AutoPostBack="True" 
                  OnSelectedIndexChanged="ddlNoTagging_SelectedIndexChanged">
</asp:DropDownList>

关键说明 #

• 所有用户选择的状态必须持久化到ViewState的DataTable中，GridView重新绑定后才能从这里恢复
• 依赖SqlDataSource自动绑定下拉框，避免手动重复绑定导致的状态丢失
• 恢复状态时先处理ddlItem，再联动刷新ddlNoTagging，确保联动逻辑正确

内容的提问来源于stack exchange，提问作者Nurul Shahida