在我的应用程序中显示 Microsoft Access“OLE 对象”

Posted 2023-05-07

【中文标题】在我的应用程序中显示 Microsoft Access“OLE 对象”

【英文标题】：Display Microsoft Access "OLE Object" in my application

【发布时间】：2010-11-17 15:38:48

【问题描述】：

我有一个包含 OLE 对象字段的 Access 数据库。我需要将此字段的内容提取为图像。最初放置在 OLE 字段中的类型无关紧要。我只需要一张代表该对象外观的图像。

这样做的主要目标是从 OLE 对象字段转移到存储在 blob 字段中的更标准的图像。

我找到了一些解析 blob 并尝试提取底层文件的示例代码。我真的在寻找按预期使用 OLE 对象的东西，而不是试图解决它们。

***上有两个类似的问题：Converting an OLE Image Object from MS Access for use in .NETExtract OLE Object (pdf) from Access DB

我打开这个问题主要是为了发布我当前的 Delphi 代码，看看是否有比我当前的代码更好的方法，如果没有，则帮助其他人。

我使用的是 Delphi 2007，但任何语言的代码都会有所帮助。

【参考方案1】：

以下是我正在使用的解决方案。这个起点来自Ms Access Ole Fields on the about.com site。

一些注意事项：

Access 似乎使用 OLE1 标准而不是 OLE2 存储对象。除了上面提到的帖子之外，我在任何地方都找不到任何确认。 Access 在 OLE1 字段前面附加它自己的标头。同样，我没有找到除帖子之外的任何文档。 我找不到直接使用 OLE1 对象的方法，我需要将其转换为 OLE2 对象。为了做到这一点，我需要 OLE1 流，它似乎没有在任何地方的 VCL 或 Win API 中实现。实现直接取自帖子，我不能说我理解它所做的一切。

一旦您拥有一个 IOLEObject，您就可以使用 OleDraw 函数在您自己的画布上绘图。那时你有一个图像并且正在关闭并运行。如果您只想显示对象，您可以使用 TOLEContainer 组件并让它处理绘图。

这是使用该单位的代码。我有一个 ADO 表，其中包含一个名为 AdoTable1Photo 的 TBlobField 类型的字段对象。

procedure TForm2.ADOTable1AfterScroll(DataSet: TDataSet);
var
  Bmp: TBitmap;
  Jpg: TJpegImage;

  OleObject: IOleObject;
  DataObject: IDataObject;
  CreateInfo: TCreateInfo;
begin

  if AdoTable1Photo.BlobSize = 0 then
    exit;

  OleObject := OleFieldToObject(AdoTable1Photo);

  // If you want to save out an image file draw let the ole object draw to
  // a bitmap canvas and then save the results.  Could be used for converting
  // a field to a true image blob instead of a OLE Object type.
  Bmp := TBitmap.Create();
  Jpg := TJpegImage.Create();

  try
    DrawOleOnBmp(OleObject, Bmp);
    Jpg.Assign(Bmp);
    Jpg.SaveToFile('C:\temp\test.jpg');
  finally
    Bmp.Free;
    Jpg.Free;
  end;

  // If just trying to display the results without converting you can attach
  // the OleObject to a OleContainer component that will handle the drawing.
  // I could not find an easy way to do this directly.  I needed to use the
  // IDataObject interace with the CreateInfo record.

  if Succeeded(OleObject.QueryInterface(IDataObject, DataObject)) then
  begin
    // Load the OLE Container control by using the IDataObject
    CreateInfo.CreateType := ctFromData;
    CreateInfo.ShowAsIcon := false;
    CreateInfo.DataObject := DataObject;
    OleContainer.CreateObjectFromInfo(CreateInfo);
  end;

  OleObject := nil;
end;

这里是将字段转换为 IOleObject 的单元。困难的部分是提取流拆分出标头并将其转换为 OLE2 对象。完成后，我实际上只使用了两个函数：OLELoad 和 OLEDraw。

unit MSAccessOleObject;

interface
uses ActiveX, Windows, Classes, ComObj, DB, Graphics;

  // This file is a modified version of the source code posted here:
  // http://forums.about.com/ab-delphi/messages?lgnF=y&msg=1865.1

  //-----------------------------------------------------------------------------
  // Converted from Ole.h
  // 
  // Used inside from OleConvertOLESTREAMToIStorage OLE Function
  // As far I know the Access Converts the OLE2 objects in OLE1 Objects
  //
  // So for read this Kind of field we must covert the OLE1 format
  // to OLE2 format so we need the OleConvertOLESTREAMToIStorage
  // and to write an OLE object to Field we need the
  // OleConvertIStorageToOLESTREAM OLE function.
  // The code here is only for reading "Ole Object" fields, but it coudld adapted
  // to write them as well. 
  //
  // OLE.h define a OLE stream that uses a vtable and callback functions. I
  // could not find a class in the VCL that implemented the OLE v1 Stream.
  type
    POleStreamVtbl = ^TOleStreamVtbl;
    TOleStreamVtbl = record
      Get: Pointer;
      Put: Pointer;
    end;

    POle1Stream = ^TOle1Stream;
    TOle1Stream = record
      pvt: POleStreamVtbl;
      lpData: Pointer; // Link to Data in .MDB file
      dwSize: Integer; // OLE Stream length (relative to position)
    end;

    POleStream = ^TPOleStream;
    TPOleStream = record
      lpstbl: POleStreamVtbl;
    end;

  //-----------------------------------------------------------------------------
  //    Microsoft Access Field Header
  //
  //  Access adds header information in front of the actual OLE stream.
  //  We need to read it to get the size in order to find the start of
  //  the actual OLE stream.
  type
    TKind=record
      case Integer of
        0: (oot: DWord); // OLE Object type code (OT_LINK, OT_EMBEDDED, OT_STATIC)
        1: (lobjTyp: LongInt); // in our case: OT_EMBEDDED
      end;

    PAccessOleObjectHeader=^TAccessOleObjectHeader;
    TAccessOleObjectHeader = record
      typ: WORD;       // Type signature (0x1C15)
      cbHdr: WORD;     // sizeof(struct OLEOBJECTHEADER) + cchName +cchClass
      lobjType: TKind; // OLE Object Type Code (OT_STATIC, OT_LINKED,OT_EMBEDDED)
      cchName: WORD;   // Count of characters in object Name (CchSz(szName) + 1))
      cchClass: WORD;  // Count of characters in class Name  (CchSz(szClss) + 1))
      ibName: WORD;    // Offset of object name in structure  (sizeof(OLEOBJECTHEADER)
      ibClass: WORD;   // Offset of class name in structure  (ibName +cchName)
      ptSize: TSmallPoint; // Original size of Object (MM_HIMETRIC)
    end;


  function CreateOle1Stream(pStm: IStream; dwSize: Integer): POle1Stream;
  procedure DeleteOle1Stream(var Ole1Stream: POle1Stream);

  // Callback Functions for OLE1 Stream
  function Get(OleStream: POLESTREAM; Pb:Pointer; cb:Integer): Integer; stdcall;
  function Put(OleStream: POLESTREAM; const Pb:Pointer; cb:Integer): Integer; stdcall;

  function OleFieldToObject(AdoField: TBlobField): IOleObject;
  procedure DrawOleOnBmp(Ole: IOleObject; Bmp: TBitmap);

implementation

uses Sysutils;


  CreateOle1Stream
  ---------------------------------------------------------------------------

function CreateOle1Stream(pStm:IStream; dwSize:Integer): POLE1Stream;
var
  cb: Int64;
begin
  Result := new(POle1Stream);
  Result.pvt := new(POleStreamVtbl);
  Result.pvt.Get := @Get;
  Result.pvt.Put := @Put;
  Result.dwSize := dwSize;
  Result.lpData := Pointer(pStm);

  // Seek to the start of the stream
  IStream(Result.lpData).Seek(0,STREAM_SEEK_SET,cb);
end;



  DeleteOle1Stream
  ---------------------------------------------------------------------------

procedure DeleteOle1Stream(var Ole1Stream: POle1Stream); // Dispose then OLE1 Stream
begin
  if Ole1Stream = Nil then
    exit;

  Dispose(Ole1Stream^.pvt);
  Dispose(Ole1Stream);
end;


  Put
  ---------------------------------------------------------------------------
  Callback function for Ole1Stream

function Put(OleStream: POLESTREAM; const Pb:Pointer; cb:Integer): Integer; stdcall;
Var
  pStream: POle1Stream;
  ulBytesWritten: longInt;
begin
  pStream:=POle1Stream(OleStream);

  if (pStream = Nil) or (pStream^.lpData=Nil) or (pb=Nil) then
  begin
    Result:=0;
    exit;
  end;

  ulBytesWritten:=0;
  if IStream(pStream^.lpData).Write(Pb,cb,@ulBytesWritten) <> S_OK then
  begin
    Result:=0;
    exit;
  end;

  pStream^.dwSize:=pStream^.dwSize+ulBytesWritten;
  Result:=cb;
end;


  Get
  ---------------------------------------------------------------------------
  Callback function for Ole1Stream

function Get(OleStream: POLESTREAM; Pb: Pointer; cb: Integer): Integer; stdcall;
Var
  pStream: POle1Stream;
  ulBytesRead: LongInt;
begin
  pStream := POle1Stream(OleStream);
  if (pStream=Nil) or (pStream^.lpData=Nil) or (pStream^.dwSize < cb)
  then
  begin
    Result := 0;
    exit;
  end;

  ulBytesRead := 0;
  if IStream(pStream^.lpData).Read(pb, cb, @ulBytesRead) <> S_OK then
  begin
    Result := 0;
    exit;
  end;

  pStream^.dwSize := pStream^.dwSize-ulBytesRead;
  Result := cb;

end;


  OleFieldToObject
  ---------------------------------------------------------------------------
  Pass in the ADO field of the "OLE Object" type and get the IOleObject
  interface back.  You can then attached that object to a OleContanier and
  let it draw itself or use the DrawOleOnBmp function to get your own bitmap
  that can be used by itself.

function OleFieldToObject(AdoField: TBlobField): IOleObject;
var

  AccessHeader: TAccessOleObjectHeader;

  FullAdoStream: TMemoryStream;
  ObjectStream: TMemoryStream;

  StreamAdapter: TStreamAdapter;
  StreamInterface: IStream;
  Ole1Stream: POle1Stream;

  OleBytes: ILockBytes;
  OleStorage: IStorage;
  OleObject: IOleObject;

begin

  FullAdoStream := nil;
  ObjectStream := nil;
  StreamAdapter := nil;
  StreamInterface := nil;
  Ole1Stream := nil;

  try
    // We need a IStorage Interface that will be used to load the OLEObject
    OleCheck( CreateILockBytesOnHGlobal(0, true, OleBytes) );
    OleCheck( StgCreateDocfileOnILockBytes(OleBytes,
      STGM_Create or STGM_READWRITE or STGM_SHARE_EXCLUSIVE or STGM_DIRECT,  0, OleStorage) );


    // We need to get the data out of the field.  Microsoft Access stores a OLE1 field
    // and not the current OLE2 format.  It also adds it's own header on the object.
    // We need to - extract the stream, remove the header, wrap the stream in an
    // IStreamInterface, wrap that inside and OLE1Stream object.

    FullAdoStream := TMemoryStream.Create();
    AdoField.SaveToStream(FullAdoStream);

    FullAdoStream.Seek(0, soBeginning);
    FullAdoStream.ReadBuffer(AccessHeader, sizeof(TAccessOleObjectHeader));

    // We could check if AccessHeader.typ = $1C15 but if the format is not
    // right something will go wrong later.


    // Seek past the header and then copy the rest of the stream to a new stream.
    FullAdoStream.Seek(AccessHeader.cbHdr, soBeginning);
    ObjectStream := TMemoryStream.Create();
    ObjectStream.CopyFrom(FullAdoStream, FullAdoStream.Size - FullAdoStream.Position);

    StreamAdapter := TStreamAdapter.Create(ObjectStream, soReference);
    StreamInterface := StreamAdapter as IStream;
    Ole1Stream := CreateOle1Stream(StreamInterface, ObjectStream.Size);

    // Now convert the OLE1 stream to OLE2 (IStorage) and load the IOleObject
    // This function seems to be slow, but I can't find anything to change
    // or any other function to use. 
    OleCheck( OleConvertOLESTREAMToIStorage(Ole1Stream, OleStorage, Nil) );
    OleCheck( OleLoad(OleStorage, IOleObject, nil, OleObject) );

  finally
    DeleteOle1Stream(Ole1Stream);
    StreamInterface := nil;
    StreamAdapter := nil;
    ObjectStream.Free;
    FullAdoStream.Free;
  end;

  result := OleObject;

end;



  DrawOleOnBmp
  ---------------------------------------------------------------------------
  Take a OleObject and draw it to a bitmap canvas.  The bitmap will be sized
  to match the normal size of the OLE Object.

procedure DrawOleOnBmp(Ole: IOleObject; Bmp: TBitmap);
var
  ViewObject2: IViewObject2;
  ViewSize: TPoint;
  AdjustedSize: TPoint;

  DC: HDC;
  R: TRect;
begin

  if Succeeded(Ole.QueryInterface(IViewObject2, ViewObject2)) then
  begin
    ViewObject2.GetExtent(DVASPECT_CONTENT, -1, nil, ViewSize);

    DC := GetDC(0);
    AdjustedSize.X := MulDiv(ViewSize.X, GetDeviceCaps(DC, LOGPIXELSX), 2540);
    AdjustedSize.Y := MulDiv(ViewSize.Y, GetDeviceCaps(DC, LOGPIXELSY), 2540);
    ReleaseDC(0, DC);

    Bmp.Height := AdjustedSize.Y;
    Bmp.Width := AdjustedSize.X;

    SetRect(R, 0, 0, Bmp.Width, Bmp.Height);

    OleDraw(Ole, DVASPECT_CONTENT, Bmp.Canvas.Handle, R);
  end
  else
  begin
    raise Exception.Create('Could not get the IViewObject2 interfact on the OleObject');
  end;

end;

end.