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',

lpBuffer);

{Free the temp path buffer}

FreeMem(lpPathBuffer, MAX_PATH);

{$ELSE}

{Get the temp file name}

GetTempFileName(GetTempDrive('C'),

'tmp',

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;

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

begin

if (Sender as TDataSource).State = dsBrowse then

LoadWMFFromDatabase;

end;

end.