インターフェイスポインタからインターフェイス/オブジェクトを取得する正しい方法はありますか？

Question

今までインターフェイスについて何も知らなかったので、実際にはthis questionに与えられたソリューションを実装しようとするのは非常に困難です。

私はIShellFolderインターフェイスへのポインタを正しく取得していると思いますが、実際にそのポインタを使用できないようです。そのポインタを持つときに、どのように使用可能なインターフェイスに到達するのですか？

以下のコードは、私がやっていることとどこで問題が疑わしいかを示しています。

まず、私のインタフェースdelarations：

' I have wrapped the interfaces in their own namespace, "BinarusShell". 
' I have declared every interface's functions/subs in the same order as they are in the .idl files of the Windows Platform SDK 7.1. 
' Every function/sub has the <PreserveSig()> attribute so that I can see the native return values when debugging. 
' I'd like to keep the question as lean as possible, so I am showing only a few functions per interface. 
' Of course, I have implemented all of them (as they are in the respective .idl file). 

Namespace BinarusShell 

    <ComImport()> _ 
    <InterfaceType(ComInterfaceType.InterfaceIsIUnknown)> _ 
    <Guid("000214FA-0000-0000-C000-000000000046")> _ 
    Public Interface IExtractIcon 

    ' The above GUID is the GUID for the UNICODE version of the interface, i.e. IExtractIconW. 
    ' Therefore, the UNICODE variant of strings is used in the parameters of the following functions. 
    ' See also the include files of the Windows SDK where this is done exactly that way as well. 

    <PreserveSig()> Function GetIconLocation(ByVal uFlags As UInteger, 
              <MarshalAs(UnmanagedType.LPWStr, SizeParamIndex:=2)> ByVal pszIconFile As String, 
              ByVal cchmax As UInteger, 
              ByRef piIndex As Integer, 
              ByRef pwFlags As UInteger) As Integer 

    ' ... 
    ' Here comes the second function (IExtractIcon has only two) ... 
    ' ...  

    End Interface 

    <ComImport()> _ 
    <InterfaceType(ComInterfaceType.InterfaceIsIUnknown)> _ 
    <Guid("000214E6-0000-0000-C000-000000000046")> _ 
    Public Interface IShellFolder 

    <PreserveSig()> Function GetUIObjectOf(<[In]()> ByVal hwndOwner As IntPtr, 
              <[In]()> ByVal cidl As UInteger, 
              <[In]()> <MarshalAs(UnmanagedType.LPArray, SizeParamIndex:=1)> ByVal apidl() As IntPtr, 
              <[In]()> <MarshalAs(UnmanagedType.LPStruct)> ByVal riid As Guid, 
              <[In](), Out()> ByRef rgfReserved As UInteger, 
              <Out()> ByRef ppv As IntPtr) As Integer 

    ' ... 
    ' Here come the other functions ... 
    ' ... 

    End Interface 

End Namespace 

第二に、私ののWindows APIの宣言、および 第三は、機能は、私は（私は立ち往生午前ところ、これがある）を実装する：

' The Windows API declarations are in class Win32Api. 
' This class is not wrapped in a certain namespace. 
' To keep this question as lean as possible, I am leaving out my declarations of constants or GUIDs. 
' I have taken all of them literally from the Windows Platform SDK 7.1. 

Public Class Win32Api 

    <DllImport("shell32.dll", CharSet:=CharSet.Auto)> _ 
    Private Shared Function SHBindToParent(<[In]()> ByVal pidl As IntPtr, 
             <[In]()> <MarshalAs(UnmanagedType.LPStruct)> ByVal riid As Guid, 
             <Out()> ByRef ppv As IntPtr, 
             <Out()> ByRef ppidlLast As IntPtr) As Integer 
    End Function 

    <DllImport("shell32.dll", CharSet:=CharSet.Auto)> _ 
    Private Shared Function SHGetKnownFolderIDList(<[In]()> <MarshalAs(UnmanagedType.LPStruct)> ByVal rfid As Guid, 
               <[In]()> ByVal dwFlags As UInteger, 
               <[In]()> ByVal hToken As IntPtr, 
               <Out()> ByRef ppidl As IntPtr) As Integer 
    End Function 

' ----------------------------------------------------- 

' The function I would like to implement is in class Win32Api as well. 
' The function at this stage does nothing which is useful for the outer world; 
' It is just meant for code which I am stepping through with the debugger. 
' The comments below show the result of every step and my understanding about what has happened. 

    Public Shared Function IconTest() As Boolean 

    Dim ui_ReturnFlags As UInteger 
    Dim i_Result As Integer 
    Dim intptr_CurrentPidlAbsolute As IntPtr, 
     intptr_ParentIShellFolder As IntPtr, 
     intptr_CurrentIExtractIcon As IntPtr 
    Dim arintptr_RelPidList(0) As IntPtr 
    Dim ishellfolder_Parent As BinarusShell.IShellFolder 
    Dim iextracticon_Extractor As BinarusShell.IExtractIcon 

    i_Result = SHGetKnownFolderIDList(FOLDERID_System, 0, 0, intptr_CurrentPidlAbsolute) 
    ' The above seems to work. i_Result is 0 which means success, and 
    ' intptr_CurrentPidlAbsolute has a reasonable value now. 

    i_Result = SHBindToParent(intptr_CurrentPidlAbsolute, IID_IShellFolder, intptr_ParentIShellFolder, arintptr_RelPidList(0)) 
    ' The above seems to work. i_Result is 0 which means success, and 
    ' intptr_ParentIShellFolder and arintptr_RelPidList(0) have reasonable values now. 

    ' Now the PROBLEMS begin. I have no clue how to get an interface/object 
    ' from intptr_ParentIShellFolder which I can use from within VB.net. 
    ' Therefore, I just have tried the following (but believing that it is wrong): 
    ishellfolder_Parent = DirectCast(Marshal.GetObjectForIUnknown(intptr_ParentIShellFolder), BinarusShell.IShellFolder) 
    ' This does not throw an error, but I have no clue what actually is happening. 
    ' Marshal.GetObjectForIUnknown, as the name implies, should return an object which 
    ' encapsulates an IUnknown interface, but I am giving a pointer to an IShellFolder 
    ' interface, so I really wonder why it doesn't freak out. The original idea 
    ' to try it that way was that I believe that IShellFolder inherits IUnknown, 
    ' so it *eventually* could work that way. Could somebody comment about that? 

    i_Result = ishellfolder_Parent.GetUIObjectOf(0, 1, arintptr_RelPidList, IID_IExtractIcon, ui_ReturnFlags, intptr_CurrentIExtractIcon) 
    ' Now this is the point where I am completely puzzled. i_Result is still 0, 
    ' which means success, but intptr_CurrentIExtractIcon is 0 as well, meaning 
    ' that something has gone horribly wrong. According to my understanding of 
    ' the MSDN documentation, GetUIObjectOf MUST NOT return S_OK if something 
    ' has gone wrong; in other words, if it returns S_OK, then intptr_CurrentIExtractIcon 
    ' MUST be set to a reasonable value. Could somebody explain what's happening? 

    ' I have left out the rest of the function because it wouldn't make any sense 
    ' to use the NULL pointer for any further action. 

    End Function 

End Class 

私が間違っていることは何ですか？ドキュメントから、私はのすべてフォルダ項目（仮想かどうか）とファイルがIExtractIconを公開しているという印象を受けました。

Answer 1

VB.netでIShellFolderインターフェイスを定義するときに、BindToFolder()関数を含めるのを忘れていました（03:00に実装するようにすべきではありません。 1時間前までのもの）。もちろん

、どこにでも記載されているように、これは私は、BindToFolder()は、インタフェース定義にGetUIObjectOf()前に来て、順番に、後者はGetDisplayNameOf()の前に来るので、IShellFolderインタフェースは、再び本当に私が何を言っているかわからない（間違った結果を生成作られたが私のコードがGetUIObjectOf()と呼ばれるときに実際にGetDisplayNameOf()が呼び出されたと想像できます。これは奇妙な結果を説明します）。

IShellFolderの定義を修正しました（つまり、欠落している機能を追加しました）。私の他のインターフェース定義（エラーなし）をダブルチェックしました。