VBA 获取属性
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VBA Get property
提问by gajo357
I have a class module MyVBAclass which has a member of a custom COM class
我有一个类模块 MyVBAclass，它有一个自定义 COM 类的成员
Private mMyCOMclass As MyCOMclass
Public Property Get InnerClass() As MyCOMclass
Set InnerClass = mMyCOMclass
End Property
Public Property Let InnerClass(value As MyCOMclass)
Set mMyCOMclass = value
End Property
Private Sub Class_Initialize()
Set mMyCOMclass = New MyCOMclass
End Sub
MyCOMclass has Clone() and CopyTo() methods implemented, Clone returns a new instance of MyCOMclass, and CopyTo just copies the properties to an already initialized object. This is the problem that I have, and it would be great if someone could explain how can avoid it.
MyCOMclass 实现了 Clone() 和 CopyTo() 方法，Clone 返回 MyCOMclass 的新实例，而 CopyTo 只是将属性复制到已初始化的对象。这是我遇到的问题，如果有人能解释如何避免它，那就太好了。
Dim MyVBAinstance As MyVBAclass
Set MyVBAinstance = New MyVBAclass
Dim COMinstance As MyCOMclass, copyOfCOM As MyCOMclass
Set COMinstance = New MyCOMclass
Set copyOfCOM = New MyCOMclass
' Do some stuff with COMinstance
Call COMinstance.CopyTo(copyOfCOM) ' Works fine
MyVBAinstance.InnerClass = COMinstance.Clone() ' Works fine even without Set
Call COMinstance.CopyTo(MyVBAinstance.InnerClass) ' DOESN'T WORK
回答by Peter Albert
The idea of object orientation is that an object hides it's members from the outside world. The GETand SETproperties act as a "gateway". This, no routine can simply override change the object underneath MyVBAinstance.InnerClass. What you need to do is:
面向对象的思想是一个对象向外界隐藏它的成员。在GET和SET特性充当“网关”。这一点，没有例程可以简单地覆盖更改下面的对象MyVBAinstance.InnerClass。你需要做的是：
Dim objTemp as As MyCOMclass
Set objTemp = New MyCOMclass 'this will reserve the memory and store the pointer in objTemp
Call COMinstance.CopyTo(objTemp) 'this will fill the allocated memory
Set MyVBAinstance.InnerClass = objTemp 'this will copy the pointer from objTemp to MyVBAinstance.InnerClass
If you want to expose some private members of your class, you need to provide the PROPERTY GETand PROPERTY SET/PROPERTY LETmethods as you are doing. GETwill be called every time you access the property - and PROPERTY SET/PROPERTY LETis called when you assign an object/value to the property.
如果要公开类的某些私有成员，则需要在执行时提供PROPERTY GET和PROPERTY SET/PROPERTY LET方法。GET将被调用每次你访问属性的时间-和PROPERTY SET/PROPERTY LET当你分配对象/值的属性被调用。
If the property is an object, you need to use PROPERTY SET- if it is of a native type (Integer, String, etc.) you must use PROPERTY LET.
In the same way, you then need to assign objects to the property with SET(e.g. Set MyVBAInstance.InnerClass = anotherObject), but native types without SET(e.g. ' MyVBAInstance.Name = "Test"`)
Thus, in your code replace LETwith SEThere:
Public Property Set InnerClass(value As MyCOMclass)
Set mMyCOMclass = value
End Property
and then also use the SETkeyword in your code:
Set MyVBAinstance.InnerClass = COMinstance.Clone()
如果属性是对象，则需要使用PROPERTY SET- 如果它是本机类型（整数、字符串等），则必须使用PROPERTY LET.
以同样的方式，然后您需要使用SET(eg Set MyVBAInstance.InnerClass = anotherObject)将对象分配给属性，但不使用SET(eg ' MyVBAInstance.Name = "Test"`) 的本机类型
因此，在您的代码中替换LET为SET：
Public Property Set InnerClass(value As MyCOMclass)
Set mMyCOMclass = value
End Property
然后也在SET你的代码中使用关键字：
Set MyVBAinstance.InnerClass = COMinstance.Clone()
