「TypeOf ... Is Child」from Parent導致破損的Excel文件

Question

我一直在追蹤這個問題好幾天，所以我想我會在這裏發佈它來幫助其他人解決同樣的問題，以及學習更多關於原因。我已經簡化了這篇文章結尾處的兩個類模塊的問題代碼。

基本上，簡化的場景是這樣的：兩個類模塊，父和子，其中子實現父。 Parent中的某處是行TypeOf Me Is Child，其中Me可以是任何對象。

從我的理解，當TypeOf...Is行被編譯爲P代碼（調試>編譯或調用方法）並保存到文件（.xlsm或.xlsb）時，它會導致文件無法正常打開。代碼可以正常運行，但是當文件保存，關閉並重新打開時，它會在打開（或打開VBE）時提示錯誤，說Invalid data format或Error accessing file. Network connection may have been lost，並且父模塊不能再打開，也不能打開任何VBA運行（在立即窗口中嘗試?1=1，它會給出相同的錯誤）。

如果使用TypeName()而不是TypeOf...Is檢查類型，則不會出現此問題（這是我在項目中使用的解決方案）。

任何人都可以更清楚地知道究竟是哪裏出了問題，或者至少證明我是在正確的軌道上引發問題（P代碼）？

PS是的，我知道父母對孩子的認識是糟糕的設計，但我接近一次性項目的結束，這是不值得花時間重新設計的。

相關鏈接：

• 解釋VBA代碼狀態，什麼是保存到文件中。 http://orlando.mvps.org/VBADecompilerMore.asp?IdC=OrlMoreWin#WhatItIs

類模塊：

家長：

Option Explicit 
' Class: Parent 

' The problem (so far as I can tell): 
' When the compiled version of the method below is saved to the file, the file 
' will no longer load properly. Upon saving and reopening the file, I get a 
' "Invalid data format" error, and the code for this class module can no longer be 
' accessed. Furthermore, no VBA code will run after this happens. Try typing "?1=1" 
' into the Immediate Window - you'll get another "Invalid data format" window. 
' Alternatively, the error will be "Error accessing file. Network connection may 
' have been lost." if the code is changed from using "Me" to "tmp" as noted in the 
' comments in DoSomething(). 

' Steps to replicate: 
' 1. Debug > Compile VBAProject. 
' 2. Save file. 
' 3. Close Excel. 
' 4. Reopen file (and may need to open VBE). 

Public Sub DoSomething() 
    ' The TypeOf...Is statement seems to be what causes the problem. 
    ' Note that checking "Me" isn't the cause of the problem (merely makes 
    ' for shorter demo code); making a "Dim tmp as Object; set tmp = new Collection" 
    ' and checking "TypeOf tmp Is Child" will cause the same problem. 
    ' Also note, changing this to use TypeName() resolves the issue. 
    ' Another note, moving the TypeOf...Is to a "Private Sub DoSomethingElse()" has 
    ' no effect on the issue. Moving it to a new, unrelated class, however, does 
    ' not cause the issue to occur. 
    If TypeOf Me Is Child Then 
     Debug.Print "Parent" 
    End If 
End Sub 

兒童：

Option Explicit 
' Class: Child 

Implements Parent 

Private Sub Parent_DoSomething() 
    Debug.Print "Child" 
End Sub 

Answer 1

VBA並不支持類的多態性。

我想你是誤解了關鍵字Implements的目的。

當你想一個類來實現的接口它使用 - 沒有其它類（好吧，至少不是真的，因爲接口在VBA是另一個類模塊對象）

見this answer for better understanding of theImplementskeyword in VBA

另請參閱this有關VBA多態性的信息