Question and Answer Database
FAQ878D.txt Save and load metafiles in a BLOB field without using DBImage
Category :VCL
Platform :All
Product :All 32 bit
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.
7/16/98 4:31:28 PM
Last Modified: 01-SEP-99