Question

我目前正在使用Excel VBA加载项来处理从一个系统到利益相关者想要查看的格式的CSV导出。我对OOP还是陌生的，但我认为这可能在Let代码中转换优先级类型，并以与输出时相同的格式存储数据。

我写了以下课程：

'Class Module "Project"
Option Explicit

Private m_sPriority As String

Property Let Priority(lInput As Long)
    Select Case lInput
        Case 1
            m_sPriority = "High"
        Case 2
            m_sPriority = "Medium"
        Case 3
            m_sPriority = "Low"
        Case Else
            m_sPriority = "No Priority"
    End Select
End Property

Property Get Priority() As String
    Priority = m_sPriority
End Property

这是测试它的模块：

'Standard Module
Option Explicit

Sub test()
        Dim Project As Project
        Set Project = New Project

        Project.Priority = 1
        Debug.Print Project.Priority
End Sub

我希望在运行此命令时看到“高”输出到控制台。

是否可以在VBA中完成此操作，或者我的代码格式错误？

Answer 1

是的，您的代码格式不正确。无论值多少钱，您都无法在.NET中做到这一点-无论是在C＃中，语法都使它变得毫不含糊：

private string _priority;
public string Priority 
{
    get { return _priority; }
    private set { _priority = value; }
}

...或在VB中：

Private _priority As String
Public Property Priority() As String
    Get
        Return _priority
    End Get
    Private Set(ByVal value As String)
        _priority = value
    End Set
End Property

属性是Long或String，不能同时是两者。 Get / Let / Set访问者在VBA中也必须保持一致。

您可以通过失去类型安全性并尽早绑定，将您的财产设为Variant来作弊，但这并不是真正的好方法从OOP开始；-）

Public Enum PriorityLevel
    NoPriority = 0
    HighPriority
    MediumPriority
    LowPriority
End Enum

Private Type InstanceState
    Priority As PriorityLevel
    '...
End Type

Private this As InstanceState

Public Property Get Priority() As Variant
    Priority = PriorityName(this.Priority)
End Property

Public Property Let Priority(ByVal value As Variant)
    this.Priority = value
End Property

Private Function PriorityName(ByVal value As PriorityLevel) As String
    Select Case value
        Case HighPriority
            PriorityName = "High"
        Case MediumPriority
            PriorityName = "Medium"
        Case LowPriority
            PriorityName= "Low"
        Case Else
            PriorityName= "Undefined"
    End Select
End Function

虽然这可以很好地工作并且表面看上去很整洁，但是当您没有编写该类时就使用它，这肯定令人惊讶：如果您 set （Let Long，您理所当然也希望Get和Long也是如此。此类请求PriorityName的只读属性：

Public Property Get Priority() As PriorityLevel
    Priority = this.Priority
End Property

Public Property Let Priority(ByVal value As PriorityLevel)
    this.Priority = value
End Property

Public Property Get PriorityName() As String
    Select Case this.Priority
        Case HighPriority
            PriorityName = "High"
        Case MediumPriority
            PriorityName = "Medium"
        Case LowPriority
            PriorityName = "Low"
        Case Else
            PriorityName = "Undefined"
    End Select
End Property

现在，早期绑定和类型安全（无论您在VBA中利用了什么）的好处显而易见：在编写分配该类型对象的Priority属性的代码时，<用于Enum类型的em> IntelliSense 指导表达式的编写：

available enum members appear in a dropdown list

此外，Enum是抽象的基础数字值，这变得无关紧要：代码现在说{{1}，而不是神奇的硬编码1 }。另外，HighPriority访问器非常简单，这非常好：Get访问器永远都不会引发任何错误，因此越简单越好。

故事的寓言：如果可以帮助的话，请不要乱动类型安全，应尽一切努力使代码早日绑定-尽可能避免使用Get和Object；尽可能将Variant投射到已知的类/接口。

例如，更喜欢此：

Object

对此：

Dim sheet As Worksheet
' Workbook.Worksheets(index) returns Object; casting it to Worksheet
Set sheet = ActiveWorkbook.Worksheets(1)
sheet.Range("A1").Value = 42

是否可以在VBA中使用不同的数据类型来进行获取和获取？

1 个答案: