Question

我有这个功能

Public Function parseEmployee(ByVal employeeId As Integer, _ 
                              ByVal ws As Worksheet) As employee
    Dim emp As New employee
    Dim empRow As Range
    If sheetContainsEmployee(employeeId, ws) Then
        Set empRow = ws.Rows(ws.Columns(ID_COLUMN).Find(employeeId).Row)
        emp.id = employeeId
        emp.Name = empRow.Cells(1, NAME_COLUMN).Value
    Else
        emp = Null ' Heres what I'd like to do
    End If

    parseEmployee = emp
End Function

如果在工作表中找不到员工，我想返回null，这可能吗？我得到一个未设置的对象或变量nblock。错误

Answer 1

只有Variant可以是Null，而是使用Nothing：

Public Function parseEmployee(ByVal employeeId As Integer, _  
                              ByVal ws As Worksheet) As employee 
    Dim emp As New employee 
    Dim empRow As Range 
    If sheetContainsEmployee(employeeId, ws) Then 
        Set empRow = ws.Rows(ws.Columns(ID_COLUMN).Find(employeeId).Row) 
        emp.id = employeeId 
        emp.Name = empRow.Cells(1, NAME_COLUMN).Value 
    Else 
        Set emp = Nothing
    End If 

    Set parseEmployee = emp
End Function

你要测试的方式：

  Dim emp As employee 
  Set emp = parseEmployee( ... )

  If emp Is Nothing Then
      Debug.Print "No employee returned."
  End If

参考：Nothing? Empty? Missing? Null?

Answer 2

我发现从函数返回Nothing会导致异常。

我所做的是编写一个带有ByRef参数的子函数，该参数是您的返回值。

而不是：

Public Function test() as SomeClass
     set test = Nothing
End Function

我写了这个：

Public Sub test(ByRef result as SomeClass)
     result = Nothing
End Sub

Answer 3

只需使用“”“或”“，哪一个可以使用，你可以尝试，如：

否则设置emp =“”“”

请注意

之间没有空格

VBA如何从函数返回null

3 个答案: