专家坐堂-请教：下拉窗口为选择值时会报错，代码那里有错？Foxtable(狐表) - 新一代数据库软件，完美融合Access、Foxpro、Excel、vb.net之优势，人人都能掌握的快速软件开发工具!

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----  请教：下拉窗口为选择值时会报错，代码那里有错？  (http://foxtable.com/bbs/dispbbs.asp?boardid=2&id=55134)

--  作者：bahamute
--  发布时间：2014/8/11 15:52:00
--  请教：下拉窗口为选择值时会报错，代码那里有错？

下拉窗口有若干复选框控件，选择之后，点击确定按钮，被选中的复选框名称生成字符串
故障现象：如果一个也未勾选，则会报错，提示“未将对象引用设置到对象的实例”

确定按钮代码：
Dim str As String
For i As Integer= 1 To 16
If e.Form.Controls("CheckBox" & i).checked = True Then
str= str & "," & e.Form.Controls("CheckBox1" & i).text
End If
Next
e.Form.DropDownBox.Value= str.trim(",")
e.Form.DropDownBox.CloseDropDown()

--  作者：有点甜
--  发布时间：2014/8/11 15:54:00
--

Dim str As String = ""

For i As Integer= 1 To 16

If e.Form.Controls("CheckBox" & i).checked = True Then

str= str & "," & e.Form.Controls("CheckBox1" & i).text

End If

Next

e.Form.DropDownBox.Value= str.trim(",")

e.Form.DropDownBox.CloseDropDown()

--  作者：Bin
--  发布时间：2014/8/11 15:55:00
--

Dim str As String=""
For i As Integer= 1 To 16
If e.Form.Controls("CheckBox" & i).checked = True Then
str= str & "," & e.Form.Controls("CheckBox1" & i).text
End If
Next
e.Form.DropDownBox.Value= str.trim(",")
e.Form.DropDownBox.CloseDropDown()

--  作者：lsy
--  发布时间：2014/8/11 16:05:00
--

Dim str As String

For i As Integer= 1 To 16

If e.Form.Controls("CheckBox" & i).checked = True Then

str= str & "," & e.Form.Controls("CheckBox1" & i).text

End If

Next

If str > "" Then

   str = str.Trim(",")

End If

e.Form.DropDownBox.Value= str

e.Form.DropDownBox.CloseDropDown()