你调用的对象是空的。 vb.net对于一些但不是所有code [英] object reference not set to an instance of an object. vb.net for some but not all code
问题描述
当我在VB.NET执行我的code，我得到的对象引用不设置到对象的实例。 vb.net。
When i execute my code in VB.NET, I get the 'object reference not set to an instance of an object. vb.net'.
我有一些项目的下拉列表。在一个项目中，code的执行没有任何问题。然而，任何其他项目，我收到错误。
I have a dropdown list with a number of items. On one item, the code executes without any issues. However, on any of the other items, I receive the error.
例如，对于ddlItemCat.SelectedValue =手机/智能手机和放大器;附件鳕eexecutes正确的，但对于ddlItemCat.SelectedValue =移动计算和放大器;附件，你会得到错误
for example, for ddlItemCat.SelectedValue = "Mobile/Smart Phone & Accessories" the cod eexecutes correctly, but for ddlItemCat.SelectedValue = "Mobile Computing & Accessories" you will get the error.
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
下面是code产生的细胞中的字段：
Here is the code which generates the cells for the fields:
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
以上code通过一个ASP表通过日tbQty4DropDownList控件执行
<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">
</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">
</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><--- Select ---></asp:ListItem>
<asp:ListItem>No</asp:ListItem>
<asp:ListItem>Yes</asp:ListItem>
</asp:DropDownList>
</asp:TableCell>
</asp:TableRow>
<asp:TableRow>
<asp:TableCell CssClass="style8">
</asp:TableCell>
<asp:TableCell CssClass="style4">
Who will be using this device?</asp:TableCell>
<asp:TableCell>
</asp:TableCell>
</asp:TableRow>
<asp:TableRow>
<asp:TableCell CssClass="style8">
</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">
</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">
</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">
</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">
</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">
</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">
</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">
</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">
</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">
</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>
</td>
</tr>
</table>
</asp:Panel>
</div>
推荐答案
所以 tb.Text 是没有或零长度（阅读：空）。您需要考虑这种可能性在code。
So tb.Text is Nothing or length of zero (read: empty). You need to account for this possibility in your code.
无论哪种，增加一个检查该条件，像这样的：
Either, add a check for that condition, like this:
If Not IsNothing(tb) AndAlso _
!String.IsNullOrEmpty(tb.Text) AndAlso _
chkTxt(tb.Text) = False Then
注：使用 AndAlso运算将其他条件短路评估，如果第一个条件是假
Note: The use AndAlso will short-circuit the evaluation of the other conditions if the first condition is False.
或
更改 chkTxt 功能逻辑，使其正确处理没有或空（长度的字符串值零），并返回假为条件，像这样的：
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
这篇关于你调用的对象是空的。 vb.net对于一些但不是所有code的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
