vba 检查未绑定控件是否具有值的正确方法
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Proper way to check if an unbound control has a value
提问by Nick Dandoulakis
Simple scenario: a form and one text box (unbound), Text1.
简单的场景：一个表单和一个文本框（未绑定）Text1。
If "" <> Text1 Then
MsgBox "Not Empty"
End If
The above code works. The expression ""<> Text1evaluates to True if the text box contain characters.
上面的代码有效。""<> Text1如果文本框包含字符，则表达式的计算结果为 True。
The opposite doesn't work, regardless of the text box is empty or not:
反之则行不通，无论文本框是否为空：
If "" = Text1 Then ' or alternatively, False = ("" <> Text1)
MsgBox "Empty!"
End If
Can you clarify this issue?
你能澄清这个问题吗？
采纳答案by Fionnuala
The textbox is usually null if it does not contain anything, this is not the same as a zero length string (""). It can often be best to use:
如果文本框不包含任何内容，则它通常为 null，这与零长度字符串 ("") 不同。通常最好使用：
If Trim(Text1 & "") = vbNullString
'Empty
This will be true if the textbox contains spaces, a zero length string or null.
如果文本框包含空格、零长度字符串或空值，则为真。
回答by Renaud Bompuis
Alternatively, I've got a small function that I find useful for checking that sort of thing when dealing with various variable types and I just want to know whether it's blank.
或者，我有一个小函数，我发现在处理各种变量类型时检查这类事情很有用，我只想知道它是否为blank。
'-----------------------------------------------------------------------------'
' True if the argument is Nothing, Null, Empty, Missing or an empty string. '
'-----------------------------------------------------------------------------'
Public Function IsBlank(arg As Variant) As Boolean
Select Case VarType(arg)
Case vbEmpty
IsBlank = True
Case vbNull
IsBlank = True
Case vbString
IsBlank = (arg = vbNullString)
Case vbObject
IsBlank = (arg Is Nothing)
Case Else
IsBlank = IsMissing(arg)
End Select
End Function
Just Made a blog posttoday about it too.
回答by Markus
I always use the function Nz (variable, valueIfNull)to check those kind of things. For example:
我总是使用函数 Nz (variable, valueIfNull)来检查这些事情。例如：
if (Len(Nz(Me.txt1, "")) > 0) then
'Me.txt1 does not contain a value
end if
Or if I want to save a textbox's value to a recordset:
或者，如果我想将文本框的值保存到记录集：
rst!Name = Nz(Me.txtName, "No name given")
