我实际上正在处理我的第一个VBA项目。（来自C ++）
我想通过实现类和多态性来改进一个已经存在的VBA项目，该项目由Microsoft Excel工作簿使用。
我的问题是：
1 - 我阅读了许多解释VBA不是面向对象编程(OOP)语言并且不支持多态性的文章/论坛。其中一些提出了使用关键字Implements的解决方法。
2 - 我还发现了一些网页，例如这个，它解释了如何使用Inherits，Overrides，Overridable，MustOverrides等关键字在VBA中执行OOP和多态性。
所以我的问题是：
VBA是一个OOP语言吗？它是否支持多态性？
OOP坐落在四个“支柱”上：
Abstraction - Abstracting logic and concepts can easily be done by defining objects in class modules. Strictly speaking, abstraction is also achieved by using meaningful identifiers and extracting procedural code into methods (class members).
Here's an example of a procedure written in VBA that demonstrates abstraction:
Public Sub Test(ByVal checkin As Date, ByVal checkout As Date, ByVal custType As CustomerType)
Dim finder As New HotelFinder
InitializeHotels finder
Debug.Print finder.FindCheapestHotel(checkin, checkout, custType)
End Sub
It's easy to tell what this Test procedure does at a glance, because the abstraction level is very high: the implementation details are abstracted away into more specialized objects and methods.
Encapsulation - Classes can have private fields exposed by properties; classes can be made PublicNotCreatable, effectively exposing types to other VBA projects - and with a little bit of effort (by exporting the class module, opening it in your favorite text editor, manually editing class attributes, and re-importing the module), you can achieve actual read-only types. The fact that there are no parameterized constructors is irrelevant - just write a factory method that takes all the parameters you like and return an instance. This is COM, and COM likes factories anyway.
Here's an example of how the HotelFinder class from the above snippet encapsulates a Collection object and only exposes it through a Property Get accessor - code outside this class simply cannot Set this reference, it's encapsulated:
Private Type TFinder
Hotels As Collection
End Type
Private this As TFinder
Public Property Get Hotels() As Collection
Set Hotels = this.Hotels
End Property
Private Sub Class_Initialize()
Set this.Hotels = New Collection
End Sub
Private Sub Class_Terminate()
Set this.Hotels = Nothing
End Sub
Polymorphism - Implements lets you implement abstract interfaces (and concrete classes, too), and then you can write code against an ISomething abstraction that can just as well be a Foo or a Bar (given Foo and Bar both implement ISomething) - and all the code ever needs to see is ISomething. Method overloading is a language feature that VBA lacks, but overloading has nothing to do with polymorphism, which is the ability to present the same interface for differing underlying forms (data types).
Here's an example of applied polymorphism - the LogManager.Register method is happy to work with any object that implements the ILogger interface; here a DebugLogger and a FileLogger - two wildly different implementations of that interface, are being registered; when LogManager.Log(ErrorLevel, Err.Description) is invoked later, the two implementations will each do their own thing; DebugLogger will output to the immediate toolwindow, and FileLogger will write an entry into a specified log file:
LogManager.Register DebugLogger.Create("MyLogger", DebugLevel)
LogManager.Register Filelogger.Create("TestLogger", ErrorLevel, "C:\Dev\VBA\log.txt")
Inheritance - VBA does not let you derive a type from another: inheritance is not supported.
Class_Inititalize事件，可以进行一些构建，但不能带参数。传递参数需要一个公共工厂函数，以创建构造函数样式的设计模式。Implements）在一定程度上实现，虽然不存在重载函数的能力（例如），每个“重载”技术上都需要一个唯一的函数名称。您可以通过将对象作为唯一参数传递到函数或子程序中，并根据属性值的变化来变化过程来解决此问题。虽然在一定程度上可以使用对象，并且MS Office应用程序是基于对象模型的，但VBA并不是真正的面向对象语言。多态性无法达到您在C ++中熟悉的程度。
Implements的一些帖子：Here。 - Daniel DušekImplments）的好例子：http://www.cpearson.com/excel/Implements.aspx - Daniel Dušek