我有问题的数据网格视图，然后是每个问题的可能答案的下拉列表。我想在点击btnSaveQuestions_Click事件时保存AnswerID（dropdownlist.selecteditem.value）。但是，在尝试之后，我的Visual Web Developer 2010版本没有给我任何错误，但是在Internet Explorer中查看（版本10.0.9200.17377，是公司策略要求我在Internet Explorer中可以使用它）时，它指出line＆＃34; Dim AnswerID as String = ddAnswer.SelectedValue＆＃34;未设置为对象的实例。任何帮助将不胜感激。
<asp:DataGrid id="dgFacilityQuestions_DataGrid" runat="server" cssClass="dgBlue" horizontalalign="center" width="90%" OnItemCreated="dgFacilityQuestions_DataGrid_ItemCreated" OnItemDataBound="dgFacilityQuestions_DataGrid_ItemDataBound" CellPadding="3"
AutoGenerateColumns="False">
<HeaderStyle backcolor="#A09CBF" />
<Columns>
<asp:BoundColumn DataField="QuestionID" ReadOnly="True" HeaderText="QuestionId" Visible="False"></asp:BoundColumn>
<asp:BoundColumn DataField="QuestionText" HeaderText="Question Text">
<ItemStyle width="60%" horizontalalign="left" />
</asp:BoundColumn>
<asp:TemplateColumn HeaderText="Answers">
<ItemTemplate>
<asp:DropdownList id="ddAnswers" runat="server" DataValueField="AnswerID" DataTextField="AnswerText"></asp:DropdownList>
</ItemTemplate>
</asp:TemplateColumn>
</Columns>
</asp:DataGrid>
Sub dgFacilityQuestionsDataGrid()
' create the SQL query that will populate the grid, then call, then bind
Dim SQLString1 As String = "SELECT QuestionID, QuestionText FROM Questions"
dgFacilityQuestions_DataGrid.DataSource = Global.ASP.Global.SQLSelect(SQLString1, "Proposal")
dgFacilityQuestions_DataGrid.DataBind()
End Sub ' End dgFacilityQuestionsDataGrid()
Sub dgFacilityQuestions_DataGrid_ItemCreated(ByVal sender As Object, ByVal e As DataGridItemEventArgs)
' datagrid formatting before data is bound to the datagrid - this does not care what data is put into the datagrid
Select Case e.Item.ItemType
Case ListItemType.Item, ListItemType.AlternatingItem, ListItemType.EditItem
' add additional attributes based on mouseover and mouse out user actions
e.Item.Attributes.Add("onMouseOver", "this.style.backgroundColor = '#A09CBF'")
e.Item.Attributes.Add("onMouseOut", "this.style.backgroundColor = '#FFFFFF'")
' add buttons as necessary for control if buttons are within the datagrid
' Cells(#) and Controls(0) correspond to what column that button resides in the table starting at zero (0)
End Select
End Sub ' End dgFacilityQuesitonsDataGrid_ItemCreated()
Sub dgFacilityQuestions_DataGrid_ItemDataBound(ByVal Sender As Object, ByVal e As DataGridItemEventArgs)
' datagrid formatting once data is bound - this depends on what data is actually produced for the datagrid
If e.Item.ItemType = ListItemType.Item Or _
e.Item.ItemType = ListItemType.AlternatingItem Then
If lblQuestionsDone.Text = "False" Then
Dim mydropdownlist As DropDownList = e.Item.FindControl("ddAnswers")
Dim SQLString As String = "SELECT AnswerID, AnswerText FROM QuestionAnswersLink WHERE QuestionID = " & e.Item.Cells(0).Text
Global.ASP.Global.refresh_ddProposal(0, SQLString, mydropdownlist)
Else
Dim mydropdownlist As DropDownList = e.Item.FindControl("ddAnswers")
Dim SQLString As String = "SELECT AnswerID, AnswerText FROM QuestionAnswersLink WHERE QuestionID = " & e.Item.Cells(0).Text
Global.ASP.Global.refresh_ddProposal(0, SQLString, mydropdownlist)
' set the showing value as the one chosen from the database
End If
End If
End Sub ' End dgFacilityQuestionsDataGrid_ItemDataBound()
Sub btnSaveQuestions_Click(sender As Object, e As EventArgs)
If btnSaveQuestions.Text = "Save Answers" Then ' questions answered for the first time
Dim i As Integer = 0
For Each dr As DataGridItem In dgFacilityQuestions_DataGrid.Items
Dim ddAnswer As DropDownList = CType(dgFacilityQuestions_DataGrid.FindControl("ddAnswers"), DropDownList)
Dim AnswerID As String = ddAnswer.SelectedValue
If AnswerID <> 0 Then
Global.ASP.Global.SQLInsert("INSERT INTO ProposalFacilityQuestionLink (ProposalFacilityID, AnswerID) VALUES ('" & lblFacilityID.Text & "','" & AnswerID & "')")
End If
i = i + 1
Next
ElseIf btnSaveQuestions.Text = "Save Changes" Then ' answers changed
End If
End Sub ' End btnSaveQuestions_Click()