Chapter 6. Property Sheet Handlers

6.2 Property Sheet Handler Interface

Now that you know how a property sheet handler works, let's discuss the interfaces involved in a little more detail.

6.2.1 IShellExtInit

The implementation of IShellExtInit is exactly the same as it was in Chapter 4. (For the details of the IShellExtInit interface, see Section 4.4 in Chapter 4.) Well, almost. The functionality provided by IShellExtInit which is used to determine which files are selected in the Exploreris generic enough to be wrapped in a class. All future extensions that must implement IShellExtInit in this book will use this class. The class is called clsDropFiles, and the complete class listing is shown in Example 6.1.

Example 6.1. clsDropFiles Class

Option Explicit

Private m_nFiles As Long
Private m_sDropFiles(  ) As String

Public Sub GetDropFiles(pDataObj As IDataObject, _ 
                        ByVal sExtension As String)

    Dim FmtEtc As FORMATETC
    Dim pMedium As STGMEDIUM
    Dim i As Long
    Dim lresult As Long
    Dim sTemp As String
    Dim lIndex As Long
    
    With FmtEtc
        .cfFormat = CF_HDROP
        .ptd = 0
        .dwAspect = DVASPECT_CONTENT
        .lIndex = -1
        .TYMED = TYMED_HGLOBAL
    End With
    
    pDataObj.GetData FmtEtc, pMedium        
    m_nFiles = DragQueryFile(pMedium.pData, &HFFFFFFFF, _ 
                             vbNullString, 0)
        
    lIndex = 0
    For i = 0 To m_nFiles - 1
        sTemp = Space(255)
        lresult = DragQueryFile(pMedium.pData, i, sTemp, Len(sTemp))
        If (lresult > 0) Then
            sTemp = Left$(sTemp, lresult)
            If LCase(Right(sTemp, 4)) = sExtension Then
                ReDim Preserve m_sDropFiles(lIndex + 1)
                m_sDropFiles(lIndex) = sTemp
                lIndex = lIndex + 1
            End If
        End If
    Next i
    
    m_nFiles = lIndex
    
    ReleaseStgMedium pMedium
    
End Sub

Public Property Get Count(  ) As Integer
    Count = m_nFiles
End Property

Public Property Get Files(nIndex As Integer) As String
    
    Files = ""
    
    If (m_nFiles) Then
        If (nIndex >= 0) And (nIndex < m_nFiles) Then
            Files = m_sDropFiles(nIndex)
        End If
    End If
        
End Property

Public Property Get SelectedFile(  ) As String
    
    SelectedFile = ""
    
    If (m_nFiles) Then
        SelectedFile = m_sDropFiles(0)
    End If
    
End Property

Now that we have a class that handles the extraction of filenames from IDataObject , implementing IShellExtInit becomes a little easier. The complete listing for IShellExtInit::Initialize is shown in Example 6.2.

Example 6.2. New Initialize Implementation

Private m_clsDropFiles As clsDropFiles

Private Sub IShellExtInit_Initialize( _ 
            ByVal pidlFolder As VBShellLib.LPCITEMIDLIST, _ 
            ByVal pDataObj As VBShellLib.IDataObject, _ 
            ByVal hKeyProgID As VBShellLib.HKEY)

    Set m_clsDropFiles = New clsDropFiles
    m_clsDropFiles.GetDropFiles pDataObj, ".rad"
    
End Sub

All IShellExtInit::Initialize needs to do is declare an instance of clsDropFiles and call the member function, GetDropFiles . GetDropFiles takes as parameters an IDataObject reference and a file filter and creates an internal array holding all of the filenames contained within the data object that have the extension .rad .

6.2.2 IShellPropSheetExt

IShellPropSheetExt contains two methods , AddPages and ReplacePage , for adding and replacing property sheets (see Table 6.1). There is really nothing unusual about this interface; we don't have to do anything crazy like vtable swapping! The implementation of this interface, on the other hand, is a wild ride, to say the least. But we'll talk about that later. For now, let's familiarize ourselves with the interface and the methods it contains.

Table6.1. IShellPropSheetExt

HRESULT STDMETHODCALLTYPE AddPages(
    LPFNADDPROPSHEETPAGE


lpfnAddPage,


LPARAM


lParam


);

HRESULT STDMETHODCALLTYPE ReplacePage(UINT


uPageID


, 
              LPFNADDPROPSHEETPAGE


lpfnReplacePage


, 
              LPARAM lParam );

typedef struct {
        long x;
        long y;
	} POINT;

typedef struct MSG {
    HWND   hwnd;
    UINT   message;
    WPARAM wParam;
    LPARAM lParam;
    DWORD  time;
    POINT  pt;
} MSG;

typedef struct { 
    HWND hwndFrom; 
    UINT idFrom; 
    UINT code; 
} NMHDR; 

typedef enum {
    PSPCB_RELEASE = 1,
    PSPCB_CREATE  = 2
} PROPSHEETCALLBACKMSG;

typedef enum {
    PSP_DEFAULT           = 0x00000000,
    PSP_DLGINDIRECT       = 0x00000001,
    PSP_USEHICON          = 0x00000002,
    PSP_USEICONID         = 0x00000004,
    PSP_USETITLE          = 0x00000008,
    PSP_RTLREADING        = 0x00000010,
    PSP_HASHELP	          = 0x00000020,
    PSP_USEREFPARENT      = 0x00000040,
    PSP_USECALLBACK       = 0x00000080,
    PSP_PREMATURE         = 0x00000400,
    PSP_HIDEHEADER        = 0x00000800,
    PSP_USEHEADERTITLE    = 0x00001000,
    PSP_USEHEADERSUBTITLE = 0x00002000
} PROPERTYSHEETFLAG;

typedef enum {
    PSN_SETACTIVE  = -200,
    PSN_KILLACTIVE = -201,
    PSN_APPLY = -202,
    PSN_RESET = -203,
    PSN_QUERYCANCEL = -209
} PROPSHEETNOTIFYMSG;

typedef struct {
    DWORD dwSize;
    DWORD dwFlags;
    HINSTANCE hInstance;
    LPCSTRVB pszTemplate;
    HICON hIcon;
    LPCSTRVB pszTitle;
    DLGPROC pfnDlgProc;
    LPARAM lParam;
    LPFNPSPCALLBACK pfnCallback;
    long pcRefParent;
    LPCTSTRVB pszHeaderTitle;
    LPCTSTRVB pszHeaderSubTitle;
} PROPSHEETPAGE;


[
    uuid(000214e9-0000-0000-c000-000000000046),
    helpstring("IShellPropSheetExt Interface"),
    odl
]
interface IShellPropSheetExt : IUnknown
{
    HRESULT AddPages([in] LPFNADDPROPSHEETPAGE lpfnAddPage, 
                     [in] LPARAM lParam);

    HRESULT ReplacePage([in] UINT uPageID, 
                        [in] LPFNADDPROPSHEETPAGE lpfnReplaceWith, 

                        [in] LPARAM lParam);
}