1

当我在 VB.NET 中执行我的代码时，我得到'对象引用未设置为对象的实例。vb.net'。

我有一个包含许多项目的下拉列表。在一项上，代码执行没有任何问题。但是，在任何其他项目上，我都会收到错误消息。

例如，对于 ddlItemCat.SelectedValue = "Mobile/Smart Phone & Accessories"，代码正确执行，但对于 ddlItemCat.SelectedValue = "Mobile Computing & Accessories"，您将收到错误消息。

Function validateInput() As Boolean
        Dim validInput As Boolean = True
        Dim backColour As System.Drawing.Color = System.Drawing.ColorTranslator.FromHtml("#F078A0")
        Dim backColourReset As System.Drawing.Color = Drawing.Color.White
        Dim errorList As String = "<span id=""errlstHdr"" style=""font-size: medium; font-weight: bold; text-align: left"">The following items must be corrected before the IT Shop Form data can be saved<span/><br /><br /><span id=""errlstDtl"" style=""font-size: small; font-weight: normal;text-align: left"">"
        Dim i As Integer
        Dim fieldName As String
        Dim tb As TextBox

        tbSurname.BackColor = backColourReset
        tbFirstname.BackColor = backColourReset
        tbPosition.BackColor = backColourReset
        tbDept.BackColor = backColourReset
        ddlCampus.BackColor = backColourReset
        tbBuilding.BackColor = backColourReset
        tbFlr.BackColor = backColourReset
        tbTelPager.BackColor = backColourReset
        ddlItemCat.BackColor = backColourReset
        msgText.Text = ""

        If chkTxt(tbSurname.Text) = False Then
            tbSurname.BackColor = backColour
            errorList += Chr(149) + "Contact Surname not entered<br />"
            validInput = False
        End If
        If chkTxt(tbFirstname.Text) = False Then
            tbFirstname.BackColor = backColour
            errorList += Chr(149) + "Contact First Name not entered<br />"
            validInput = False
        End If
        If chkTxt(tbPosition.Text) = False Then
            tbPosition.BackColor = backColour
            errorList += Chr(149) + "Contact Position not entered<br />"
            validInput = False
        End If
        If chkTxt(tbDept.Text) = False Then
            tbDept.BackColor = backColour
            errorList += Chr(149) + "Contact Department not entered<br />"
            validInput = False
        End If
        If chkTxt(ddlCampus.SelectedValue) = False Then
            ddlCampus.BackColor = backColour
            errorList += Chr(149) + "Contact Campus not entered<br />"
            validInput = False
        End If
        If chkTxt(tbBuilding.Text) = False Then
            tbBuilding.BackColor = backColour
            errorList += Chr(149) + "Contact Building not entered<br />"
            validInput = False
        End If
        If chkTxt(tbFlr.Text) = False Then
            tbFlr.BackColor = backColour
            errorList += Chr(149) + "Contact Floor not entered<br />"
            validInput = False
        End If
        If chkTxt(tbTelPager.Text) = False Then
            tbTelPager.BackColor = backColour
            errorList += Chr(149) + "Contact Phone or Pager not entered<br />"
            validInput = False
        End If
        If chkTxt(ddlItemCat.SelectedValue) = False Then
            ddlItemCat.BackColor = backColour
            errorList += Chr(149) + "Item Category not selected<br />"
            validInput = False
        End If


        If ddlItemCat.SelectedValue = "Mobile/Smart Phone & Accessories" Then
            If chkTxt(ddlNewService3.SelectedValue) = False Then
                ddlNewService3.BackColor = backColour
                errorList += Chr(149) + "New Service not selected<br />"
                validInput = False
            End If
            For i = 1 To ddlQty3.SelectedValue
                If ddlNewService3.SelectedValue = "No" Then
                    fieldName = "tbMobNo3" + i.ToString
                    tb = TryCast(FindControl(fieldName), TextBox)
                    If Not IsNothing(tb) And chkTxt(tb.Text) = False Then
                        tb.BackColor = backColour
                        errorList += Chr(149) + "Service Mobile Number not entered<br />"
                        validInput = False
                    End If
                End If
                fieldName = "tbSurname3" + i.ToString
                tb = TryCast(FindControl(fieldName), TextBox)
                If Not IsNothing(tb) And chkTxt(tb.Text) = False Then
                    tb.BackColor = backColour
                    errorList += Chr(149) + "User Surname not entered<br />"
                    validInput = False
                End If
                fieldName = "tbFirstname3" + i.ToString
                tb = TryCast(FindControl(fieldName), TextBox)
                If Not IsNothing(tb) And chkTxt(tb.Text) = False Then
                    tb.BackColor = backColour
                    errorList += Chr(149) + "User First Name not entered<br />"
                    validInput = False
                End If
            Next i
        End If

        If ddlItemCat.SelectedValue = "Mobile Computing & Accessories" Then
            If chkTxt(ddlOldDevice4.SelectedValue) = False Then
                ddlOldDevice4.BackColor = backColour
                errorList += Chr(149) + "New Service not selected<br />"
                validInput = False
            End If
            For i = 1 To tbQty4.SelectedValue
                If ddlOldDevice4.SelectedValue = "Yes" Then
                    fieldName = "tbTelPager4" + i.ToString
                    tb = TryCast(FindControl(fieldName), TextBox)
            ‘THIS IS WHERE THE ERROR OCCURS ON NEXT LINE                    
If Not IsNothing(tb) And chkTxt(tb.Text) = False Then
                        tb.BackColor = backColour
                        errorList += Chr(149) + "Service Mobile Number not entered<br />"
                        validInput = False
                    End If
                End If

                fieldName = "tbFirstname4" + i.ToString
                tb = TryCast(FindControl(fieldName), TextBox)
                If Not IsNothing(tb) And chkTxt(tb.Text) = False Then
                    tb.BackColor = backColour
                    errorList += Chr(149) + "User First Name not entered<br />"
                    validInput = False
                End If
                fieldName = "tbSurname4" + i.ToString
                tb = TryCast(FindControl(fieldName), TextBox)
                If Not IsNothing(tb) And chkTxt(tb.Text) = False Then
                    tb.BackColor = backColour
                    errorList += Chr(149) + "User Surname not entered<br />"
                    validInput = False
                End If
            Next i
        End If

        msgText.Text = errorList + "<span/>"
        Return validInput
    End Function

请帮忙

这是为字段生成单元格的代码：

Sub addRowsToMobComputingTable()
        Dim tbChk As TextBox
        Dim fieldName As String

        Dim rowCount As Integer = tbQty4.SelectedValue
        If rowCount = 1 Then ' additional rows are not required
            Return
        End If
        For i = 2 To rowCount
            ' check to ensure field doesn't exist
            fieldName = "tbSurname4" + i.ToString
            tbChk = TryCast(FindControl(fieldName), TextBox)
            If IsNothing(tbChk) Then
                For j = 0 To 10
                    Dim tempRow As New TableRow
                    Dim tempCell1 As New TableCell
                    Dim tempCell2 As New TableCell
                    Dim tempCell3 As New TableCell
                    Dim tb As New TextBox
                    Dim lbl As New Label
                    Try
                        Select Case j

                            Case 0
                                tempCell1.Text = ""
                                tempCell1.CssClass = "style8"
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "-----------------"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tempCell3.Text = ""
                                tempCell3.CssClass = "style8"
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 1
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Surname"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 144
                                tb.ID = "tbSurname4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 2
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "First Name"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 142
                                tb.ID = "tbFirstname4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 3
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Contact No."
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 186
                                tb.ID = "tbTelPager4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 4
                                tempCell1.Text = ""
                                tempCell1.CssClass = "style8"
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Position"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 295
                                tb.ID = "tbPosition4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 5
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Department"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 252
                                tb.ID = "tbDept4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 6
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Campus"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 252
                                tb.ID = "ddlCampus4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 7
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Building"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 252
                                tb.ID = "tbBuilding4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 8
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Floor"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 252
                                tb.ID = "tbFlr4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 9
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                lbl.ID = "lblAsset4" + i.ToString
                                lbl.Text = "Asset No. of old device"
                                If ddlOldDevice4.SelectedValue = "Yes" Then
                                    lbl.Visible = True
                                Else
                                    lbl.Visible = False
                                End If
                                tempCell2.CssClass = "style8"
                                tempCell2.Controls.Add(lbl)
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 144
                                If ddlOldDevice4.SelectedValue = "Yes" Then
                                    tb.Visible = True
                                Else
                                    tb.Visible = False
                                End If
                                tb.ID = "tbAsset4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                            Case 10
                                tempCell1.Text = ""
                                tempRow.Cells.Add(tempCell1)
                                tempCell2.Text = "Additional comments"
                                tempCell2.CssClass = "style8"
                                tempRow.Cells.Add(tempCell2)
                                tb.Width = 340
                                tb.Rows = 4
                                tb.TextMode = TextBoxMode.MultiLine
                                tb.ID = "tbComments4" + i.ToString
                                tempCell3.Controls.Add(tb)
                                tempRow.Cells.Add(tempCell3)
                                tblMobComp.Rows.Add(tempRow)
                        End Select
                    Catch
                    End Try
                Next j
            End If
        Next i

    End Sub

上面的代码通过“tbQty4”下拉列表控件通过 ASP 表执行：

<div id="Mobile Computing">   
    <asp:Panel ID="pnlMobComp" runat="server" Visible="False">
        <span class="style5">Mobile Computing</span><br />
        <br />
        <asp:Table ID="tblMobComp" runat="server" 
            Style="width: 46%;" ViewStateMode="Enabled">
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Quantity required?</asp:TableCell>
                <asp:TableCell>
                    <asp:DropDownList ID="tbQty4" runat="server" OnSelectedIndexChanged="addRowsToMobComputingTable"
                        AutoPostBack="True">
                        <asp:ListItem>1</asp:ListItem>
                        <asp:ListItem>2</asp:ListItem>
                        <asp:ListItem>3</asp:ListItem>
                        <asp:ListItem>4</asp:ListItem>
                        <asp:ListItem>5</asp:ListItem>
                        <asp:ListItem>6</asp:ListItem>
                        <asp:ListItem>7</asp:ListItem>
                        <asp:ListItem>8</asp:ListItem>
                        <asp:ListItem>9</asp:ListItem>
                        <asp:ListItem>10</asp:ListItem>
                        <asp:ListItem>11</asp:ListItem>
                        <asp:ListItem>12</asp:ListItem>
                        <asp:ListItem>13</asp:ListItem>
                        <asp:ListItem>14</asp:ListItem>
                        <asp:ListItem>15</asp:ListItem>
                        <asp:ListItem>16</asp:ListItem>
                        <asp:ListItem>17</asp:ListItem>
                        <asp:ListItem>18</asp:ListItem>
                        <asp:ListItem>19</asp:ListItem>
                        <asp:ListItem>20</asp:ListItem>
                    </asp:DropDownList>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Replacing an old device?</asp:TableCell>
                <asp:TableCell>
                    <asp:DropDownList ID="ddlOldDevice4" runat="server" AutoPostBack="True" CssClass="style2"
                        OnSelectedIndexChanged="ddlOldDevice4_SelectedIndexChanged">
                        <asp:ListItem>&lt;--- Select ---&gt;</asp:ListItem>
                        <asp:ListItem>No</asp:ListItem>
                        <asp:ListItem>Yes</asp:ListItem>
                    </asp:DropDownList>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Who will be using this device?</asp:TableCell>
                <asp:TableCell>
                    &nbsp;</asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Surname</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbSurname4" runat="server" Width="144px"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    First Name</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbFirstname4" runat="server" Width="142px"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Position</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbPosition4" runat="server" Width="295px"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Department</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbDept4" runat="server" CssClass="style2" Width="252px"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Campus</asp:TableCell>
                <asp:TableCell>
                    <asp:DropDownList ID="ddlCampus4" runat="server" CssClass="style2">
                        <asp:ListItem>Austin</asp:ListItem>
                        <asp:ListItem>Repat</asp:ListItem>
                        <asp:ListItem>Talbot</asp:ListItem>
                        <asp:ListItem>Other</asp:ListItem>
                    </asp:DropDownList>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Building</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbBuilding4" runat="server" CssClass="style2" Width="307px"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Floor</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbFlr4" runat="server" CssClass="style2"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    Contact No.</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbTelPager4" runat="server" CssClass="style2" Width="186px"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style8">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style4">
                    <asp:Label ID="lblAsset4" runat="server" Text="Asset No. of old device"></asp:Label>
                </asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbAsset4" runat="server" Width="144px"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
            <asp:TableRow>
                <asp:TableCell CssClass="style9">
                    &nbsp;</asp:TableCell>
                <asp:TableCell CssClass="style12">
                    Additional comments</asp:TableCell>
                <asp:TableCell>
                    <asp:TextBox ID="tbComments4" runat="server" Width="340px" Rows="4" TextMode="MultiLine"></asp:TextBox>
                </asp:TableCell>
            </asp:TableRow>
        </asp:Table>
        <table style="width: 46%;">
            <tr>
                <td>
                    &nbsp;</td>
            </tr>
        </table>
    </asp:Panel>
    </div>
4

1 回答 1

1

So tb.Text is Nothing or length of zero (read: empty). You need to account for this possibility in your code.

Either, add a check for that condition, like this:

If Not IsNothing(tb) AndAlso _
   !String.IsNullOrEmpty(tb.Text) AndAlso _
   chkTxt(tb.Text) = False Then

Note: The use AndAlso will short-circuit the evaluation of the other conditions if the first condition is False.

OR

Change the logic in the chkTxt function so that it properly handles a string value of Nothing or empty (length of zero) and returns False for that condition, like this:

Public Function chkTxt(text As String) As Boolean
    If String.IsNullOrEmpty(text) Then
        Return False
    End If

    ' Put normal check text logic here
End Function
于 2013-10-15T00:56:06.063 回答