Array as a Class Member

问题

I'm designing a dynamic buffer for outgoing messages. The data structure takes the form of a queue of nodes that have a Byte Array buffer as a member. Unfortunately in VBA, Arrays cannot be public members of a class.

For example, this is a no-no and will not compile:

'clsTest

Public Buffer() As Byte

You will get the following error: "Constants, fixed-length strings, arrays, user-defined types and Declare statements not allowed as Public members of object modules"

Well, that's fine, I'll just make it a private member with public Property accessors...

'clsTest

Private m_Buffer() As Byte

Public Property Let Buffer(buf() As Byte)
    m_Buffer = buf
End Property

Public Property Get Buffer() As Byte()
    Buffer = m_Buffer
End Property

...and then a few tests in a module to make sure it works:

'mdlMain

Public Sub Main()
    Dim buf() As Byte
    ReDim buf(0 To 4)

    buf(0) = 1
    buf(1) = 2
    buf(2) = 3
    buf(3) = 4


    Dim oBuffer As clsTest
    Set oBuffer = New clsTest

    'Test #1, the assignment
    oBuffer.Buffer = buf    'Success!

    'Test #2, get the value of an index in the array
'    Debug.Print oBuffer.Buffer(2)   'Fail
    Debug.Print oBuffer.Buffer()(2)    'Success!  This is from GSerg's comment

    'Test #3, change the value of an index in the array and verify that it is actually modified
    oBuffer.Buffer()(2) = 27
    Debug.Print oBuffer.Buffer()(2)  'Fail, diplays "3" in the immediate window
End Sub

Test #1 works fine, ~~but Test #2 breaks, Buffer is highlighted, and the error message is "Wrong number of arguments or invalid property assignment"~~

Test #2 now works! GSerg points out that in order to call the Property Get Buffer() correctly and also refer to a specific index in the buffer, TWO sets of parenthesis are necessary: oBuffer.Buffer()(2)

Test #3 fails - the original value of 3 is printed to the Immediate window. GSerg pointed out in his comment that the Public Property Get Buffer() only returns a copy and not the actual class member array, so modifications are lost.

How can this third issue be resolved make the class member array work as expected?

(I should clarify that the general question is "VBA doesn't allow arrays to be public members of classes. How can I get around this to have an array member of a class that behaves as if it was for all practical purposes including: #1 assigning the array, #2 getting values from the array, #3 assigning values in the array and #4 using the array directly in a call to CopyMemory (#3 and #4 are nearly equivalent)?)"

回答1:

So it turns out I needed a little help from OleAut32.dll, specifically the 'VariantCopy' function. This function faithfully makes an exact copy of one Variant to another, including when it is ByRef!

'clsTest

Private Declare Sub VariantCopy Lib "OleAut32" (pvarDest As Any, pvargSrc As Any)

Private m_Buffer() As Byte

Public Property Let Buffer(buf As Variant)
    m_Buffer = buf
End Property

Public Property Get Buffer() As Variant
    Buffer = GetByRefVariant(m_Buffer)
End Property

Private Function GetByRefVariant(ByRef var As Variant) As Variant
    VariantCopy GetByRefVariant, var
End Function

With this new definition, all the tests pass!

'mdlMain

Public Sub Main()
    Dim buf() As Byte
    ReDim buf(0 To 4)

    buf(0) = 1
    buf(1) = 2
    buf(2) = 3
    buf(3) = 4


    Dim oBuffer As clsTest
    Set oBuffer = New clsTest

    'Test #1, the assignment
    oBuffer.Buffer = buf    'Success!

    'Test #2, get the value of an index in the array
    Debug.Print oBuffer.Buffer()(2)    'Success!  This is from GSerg's comment on the question

    'Test #3, change the value of an index in the array and verify that it is actually modified
    oBuffer.Buffer()(2) = 27
    Debug.Print oBuffer.Buffer()(2)  'Success! Diplays "27" in the immediate window
End Sub

回答2:

Not the most elegant solution, but modeling from the code you provided...

In clsTest:

Option Explicit

Dim ArrayStore() As Byte

Public Sub AssignArray(vInput As Variant, Optional lItemNum As Long = -1)
    If Not lItemNum = -1 Then
        ArrayStore(lItemNum) = vInput
    Else
        ArrayStore() = vInput
    End If
End Sub

Public Function GetArrayValue(lItemNum As Long) As Byte
    GetArrayValue = ArrayStore(lItemNum)
End Function

Public Function GetWholeArray() As Byte()
    ReDim GetWholeArray(LBound(ArrayStore) To UBound(ArrayStore))
    GetWholeArray = ArrayStore
End Function

And in mdlMain:

Sub test()
Dim buf() As Byte
Dim bufnew() As Byte
Dim oBuffer As New clsTest

    ReDim buf(0 To 4)
    buf(0) = 1
    buf(1) = 2
    buf(2) = 3
    buf(3) = 4

    oBuffer.AssignArray vInput:=buf
    Debug.Print oBuffer.GetArrayValue(lItemNum:=2)

    oBuffer.AssignArray vInput:=27, lItemNum:=2
    Debug.Print oBuffer.GetArrayValue(lItemNum:=2)

    bufnew() = oBuffer.GetWholeArray
    Debug.Print bufnew(0)
    Debug.Print bufnew(1)
    Debug.Print bufnew(2)
    Debug.Print bufnew(3)

End Sub

I added code to pass the class array to another array to prove accessibility.

Even though VBA won't allow us to pass arrays as properties, we can still use Functions to pick up where properties fall short.

回答3:

@Blackhawk,

I know it is an old post, but thought I'd post it anyway.

Below is a code I used to add an array of points to a class, I used a subclass to define the individual points, it sounds your challenge is similar:

Mainclass tCurve

Private pMaxAmplitude As Double
Private pCurvePoints() As cCurvePoint

Public cDay As Date
Public MaxGrad As Double

Public GradChange As New intCollection
Public TideMax As New intCollection
Public TideMin As New intCollection
Public TideAmplitude As New intCollection
Public TideLow As New intCollection
Public TideHigh As New intCollection

Private Sub Class_Initialize()

    ReDim pCurvePoints(1 To 1500)
    ReDim curvePoints(1 To 1500) As cCurvePoint

    Dim i As Integer

    For i = 1 To 1500
        Set Me.curvePoint(i) = New cCurvePoint
    Next

End Sub

Public Property Get curvePoint(Index As Integer) As cCurvePoint

    Set curvePoint = pCurvePoints(Index)

End Property

Public Property Set curvePoint(Index As Integer, Value As cCurvePoint)

    Set pCurvePoints(Index) = Value

End Property

subclass cCurvePoint

Option Explicit

Private pSlope As Double
Private pCurvature As Double
Private pY As Variant
Private pdY As Double
Private pRadius As Double
Private pArcLen As Double
Private pChordLen As Double

Public Property Let Slope(Value As Double)
    pSlope = Value
End Property

Public Property Get Slope() As Double
    Slope = pSlope
End Property

Public Property Let Curvature(Value As Double)
    pCurvature = Value
End Property

Public Property Get Curvature() As Double
    Curvature = pCurvature
End Property

Public Property Let valY(Value As Double)
    pY = Value
End Property

Public Property Get valY() As Double
    valY = pY
End Property

Public Property Let Radius(Value As Double)
    pRadius = Value
End Property

Public Property Get Radius() As Double
    Radius = pRadius
End Property

Public Property Let ArcLen(Value As Double)
    pArcLen = Value
End Property

Public Property Get ArcLen() As Double
    ArcLen = pArcLen
End Property

Public Property Let ChordLen(Value As Double)
    pChordLen = Value
End Property

Public Property Get ChordLen() As Double
    ChordLen = pChordLen
End Property

Public Property Let dY(Value As Double)
    pdY = Value
End Property

Public Property Get dY() As Double
    dY = pdY
End Property

This will create a tCurve with 1500 tCurve.Curvepoints().dY (for example)

The trick is to get the index process correct in the main class !

Good luck !

来源：https://stackoverflow.com/questions/25328975/array-as-a-class-member

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arrays

vba

class-members