Question

以下代码中的函数IsNull(char)始终返回true。为什么呢？

StrText从文本字段获取它，值为：

strText = +  96666

给我一个问题的特定部分：

 If intCounter = 1 And strChar = "+" Then
            For Count = intCounter + 1 To Len(strText)
                Char = Mid(strText, Count, 1)
                If IsNull(Char) = True Then
                    Count = Count + 1
                End If
                If IsNumeric(Char) And Char <> "0" Then
                    Exit For
                    MsgBox "Problem"
                End If
            Next Count
        End If

完整的功能是：

Public Function NumbersOnly(ByVal strText As String) As Boolean
    Dim intCounter As Integer
    Dim strChar As String
    Dim Count As Integer
    Dim Char As String
    strText = Trim(strText)
    For intCounter = 1 To Len(strText)
        strChar = Mid(strText, intCounter, 1)
        If intCounter = 1 And IsNumeric(strChar) = False And strChar <> "+" Then
            NumbersOnly = False
            Exit Function
        End If
        If intCounter = 1 And strChar = "+" Then
            For Count = intCounter + 1 To Len(strText)
                Char = Mid(strText, Count, 1)
                If IsNull(Char) = True Then
                    Count = Count + 1
                End If
                If IsNumeric(Char) And Char <> "0" Then
                    Exit For
                    MsgBox "Problem"
                End If
            Next Count
        End If
        If intCounter <> 1 And (IsNumeric(strChar) = False And strChar <> " ") Then
            NumbersOnly = False
            Exit Function
        End If
    Next intCounter
    NumbersOnly = True
End Function

Answer 1

字符串被初始化为空字符串，而不是null或什么都没有。

考虑以下子程序：

Sub test()
    Dim char As String

    If IsNull(char) Then
        Debug.Print "I can't get here."
    ElseIf char = "" Then
        Debug.Print "HELLO THERE!"
    End If

    char = "sometext"
    If IsNull(char) Then
        Debug.Print "I can't get here."
    ElseIf char = "" Then
        Debug.Print "Now this fails too"
    Else
        Debug.Print "Hello Again."
    End If
End Sub

简而言之，您不想检查您的char变量是否为空，您想检查它是否为空字符串。

IsNull始终返回True

1 个答案: