WhiteUnicorn

	#WhiteUnicorn/ StartPage/ Documentation/DelphiFAQ >

Frequently Asked Questions

Save and load metafiles in a BLOB field without using DBImage

Question:

How can I save and load metafiles in a BLOB field without using the DBImage component?

Answer:

The following example demonstrates saving metafile images to a

database as they exist on the disk, preserving any Placeable metafile

headers that may be present in the Metafile. The image is displayed

from the database in a TImage component.



Example:



unit Unit1;



interface



{$IFDEF WIN32}

  uses

    Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,

      Dialogs, StdCtrls, ExtCtrls, DBCtrls, Grids, DBGrids, Db,

      DBTables;

{$ELSE}

uses

  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,

  Forms, Dialogs, DBTables, DB, Grids, DBGrids, ExtCtrls, StdCtrls;

{$ENDIF}



type

  TForm1 = class(TForm)

    Table1: TTable;

    DataSource1: TDataSource;

    DBGrid1: TDBGrid;

    Image1: TImage;

    Button1: TButton;

    Table1Name: TStringField;

    Table1WMF: TBlobField;

    OpenDialog1: TOpenDialog;

    procedure FormCreate(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

    procedure Button1Click(Sender: TObject);

    procedure DataSource1DataChange(Sender: TObject; Field: TField);

  private

    { Private declarations }

    FileName : string; {Used to hold a temp file name}

    procedure LoadWMFFromDatabase; {loads a WMF from the database}

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.DFM}



procedure TForm1.FormCreate(Sender: TObject);

begin

 {Used for loading metafiles}

  OpenDialog1.Filter := 'Metafiles (*.wmf)|*.wmf';

  OpenDialog1.Options := [ofHideReadOnly, ofNoChangeDir];

  Image1.Stretch := true;

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

 {Erase the temp file if it exists}

  if FileName <> '' then

    DeleteFile(FileName);

end;



{This function gets a temporary file name form the system}

function GetTemporaryFileName : string;

{$IFNDEF WIN32}

  const MAX_PATH = 144;

{$ENDIF}

var

 {$IFDEF WIN32}

  lpPathBuffer : PChar;

 {$ENDIF}

  lpbuffer : PChar;

begin

 {Get the file name buffer}

  GetMem(lpBuffer, MAX_PATH);

 {$IFDEF WIN32}

 {Get the temp path buffer}

  GetMem(lpPathBuffer, MAX_PATH);

 {Get the temp path}

  GetTempPath(MAX_PATH, lpPathBuffer);

 {Get the temp file name}

  GetTempFileName(lpPathBuffer,

                  'tmp',

                  0,

                  lpBuffer);

 {Free the temp path buffer}

  FreeMem(lpPathBuffer, MAX_PATH);

 {$ELSE}

 {Get the temp file name}

  GetTempFileName(GetTempDrive('C'),

                  'tmp',

                  0,

                  lpBuffer);

 {$ENDIF}

 {Create a pascal string containg}

 {the  temp file name and return it}

  result := StrPas(lpBuffer);

 {Free the file name buffer}

  FreeMem(lpBuffer, MAX_PATH);

end;



procedure TForm1.LoadWMFFromDatabase;

var

  FileStream: TFileStream; {a temp file}

  BlobStream: TBlobStream; {the WMF Blob}

begin

  Image1.Picture.Metafile.Assign(nil);

 {Create a blob stream for the WMF blob}

  BlobStream := TBlobStream.Create(Table1WMF, bmRead);

  if BlobStream.Size = 0 then begin

   BlobStream.Free;

   Exit;

  end;

 {if we have a temp file then erase it}

  if FileName <> '' then

    DeleteFile(FileName);

 {Get a temp file name}

  FileName := GetTemporaryFileName;

 {Create a temp file stream}

  FileStream := TFileStream.Create(FileName,

                                   fmCreate or fmOpenWrite);

 {Copy the blob to the temp file}

  FileStream.CopyFrom(BlobStream, BlobStream.Size);

 {Free the streams}

  FileStream.Free;

  BlobStream.Free;

 {Dispaly the image}

  Image1.Picture.Metafile.LoadFromFile(FileName);

end;



{Save a wmf file to the database}

procedure TForm1.Button1Click(Sender: TObject);

var

  FileStream: TFileStream; {to load the wmf file}

  BlobStream: TBlobStream; {to save to the blob}

begin

 {Allow the button to repaint}

  Application.ProcessMessages;

  if OpenDialog1.Execute then begin

   {Turn off the button}

    Button1.Enabled := false;

   {Assign the avi file name to read}

    FileStream := TFileStream.Create(OpenDialog1.FileName,

                                     fmOpenRead);

    Table1.Edit;

   {Create a BlobStream for the field Table1WMF}

    BlobStream := TBlobStream.Create(Table1WMF, bmReadWrite);

   {Seek to the Begginning of the stream}

    BlobStream.Seek(0, soFromBeginning);

   {Delete any data that may be there}

    BlobStream.Truncate;

   {Copy from the FileStream to the BlobStream}

    BlobStream.CopyFrom(FileStream, FileStream.Size);

   {Free the streams}

    FileStream.Free;

    BlobStream.Free;

   {Post the record}

    Table1.Post;

   {Load the metafile in to a TImage}

    LoadWMFFromDatabase;

   {Enable the button}

    Button1.Enabled := true;

  end;

end;



procedure TForm1.DataSource1DataChange(Sender: TObject; Field: TField);

begin

  if (Sender as TDataSource).State = dsBrowse then

    LoadWMFFromDatabase;

end;



end.

	#WhiteUnicorn/ StartPage/ Documentation/DelphiFAQ >

	Anastasija aka WhiteUnicorn	LiveJournal PhotoFile