如果 [ComboBox] 是 VBA/Access 2007 中的 Null 语句
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If [ComboBox] Is Null Statement in VBA/Access 2007
提问by myClone
I have a form with one ComboBox (YearToBeBuilt) and two textBox fields (Costand YearofExpenditureCost). All controls are linked to a main table and the table is updated once the selections/entries have been made on the form.
我有一个包含一个 ComboBox ( YearToBeBuilt) 和两个 textBox 字段 (Cost和YearofExpenditureCost)的表单。所有控件都链接到一个主表，一旦在表单上进行了选择/条目，该表就会更新。
I have written a procedure in VB called ReCalcIt()which performs the following procedure when called:
我在 VB 中编写了一个调用的过程，ReCalcIt()它在调用时执行以下过程：
Private Sub ReCalcIt()
If Me.YearToBeBuilt = "" Then
Me.YearofExpenditureCost = Me.Cost
Else
Me.YearofExpenditureCost = Me.Cost * (1 + 0.031) ^ (Me.YearToBeBuilt - 2010)
End If
End Sub
When I wrote this I thoughtthat this would do the following:
当我写这篇文章时，我认为这会做以下事情：
If the ComboBox [YearToBeBuilt]is blank (e.g.-no selection made) then
the textbox [YearOfExpenditureCost]will return the value of the TextBox [Cost]. Else, the calculation for YearofExpenditureCostis performed.
如果 ComboBox[YearToBeBuilt]为空（例如，未进行选择），则文本框[YearOfExpenditureCost]将返回 TextBox 的值[Cost]。否则，YearofExpenditureCost执行的计算。
But this is not working the way it should
但这并不像它应该的那样工作
What am I doing wrong? I am a VBA n00b so perhaps my syntax is incorrect?
我究竟做错了什么？我是 VBA n00b，所以也许我的语法不正确？
回答by CristiC
Try it with
试试看
If Len(Me.YearToBeBuilt & vbNullString) = 0
So the code will look like this:
所以代码看起来像这样：
Private Sub ReCalcIt()
If Len(Me.YearToBeBuilt & vbNullString) = 0 Then
Me.YearofExpenditureCost = Me.Cost
Else
Me.YearofExpenditureCost = Me.Cost * (1 + 0.031) ^ (Me.YearToBeBuilt - 2010)
End If
End Sub
回答by Fionnuala
The usual way is to say:
通常的说法是：
If IsNull(MyControl) Then
See also: Access VBA: If Form Value <> NULL then run query else, end if. - not doing anything
回答by Dr Xorile
It seems to me that this might be dependent on the format of the combo box? If it's a number, then
在我看来，这可能取决于组合框的格式？如果是数字，那么
If Len(Me.YearToBeBuilt & vbNullString) = 0
doesn't work. Because the Me.YearToBeBuilt has a value of 0, and so the above returns 1.
不起作用。因为 Me.YearToBeBuilt 的值为 0，所以上面的返回 1。
I'm wondering if there is a more robust method? Maybe
我想知道是否有更强大的方法？也许
Me.YearToBeBuilt.ListIndex = -1
