Question

I use the Delphi LoadFromFile function to insert Table1BLOBFIELD.LoadFromFile
(‘C:\xxx.avi’) and the SaveToFile command to retrieve.
This inserting/retrieving is rather timeconsuming (several minutes). It
would be nice if I could show a kind of progressbar (instead of only an
hourglass-shaped cursor).
When using SaveToFile I can perhaps use a timer and check the filesize
(although this doesn’t seem to work without threads). But this is no
solution for LoadFromFile.
Does anyone have a particular solution, a hint,…?
Thanks in advance

Answer 1

Here a simple example of how to subclass TFileStream and how to add an OnProgress event to it:

unit Unit1;

interface

uses
  SysUtils, Classes, Controls, Forms, XPMan, Db, ComCtrls, StdCtrls, AdoDB;

type
  TStreamProgressEvent = procedure(Sender: TObject;
    Percentage: Single) of object;

  TProgressFileStream = class(TFileStream)
  private
    FOnProgress: TStreamProgressEvent;
    FProcessed: Int64;
    FSize: Int64;
  public
    procedure InitProgressCounter(ASize: Int64);
    function Read(var Buffer; Count: Integer): Integer; override;
    function Write(const Buffer; Count: Integer): Integer; override;
    property OnProgress: TStreamProgressEvent read FOnProgress
      write FOnProgress;
  end;

  TForm1 = class(TForm)
    ADOQuery1: TADOQuery;
    ADOQuery1ID: TAutoIncField;
    ADOQuery1Blob: TBlobField;
    Button1: TButton;
    ProgressBar: TProgressBar;
    procedure Button1Click(Sender: TObject);
  private
    procedure StreamProgress(Sender: TObject; Percentage: Single);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TProgressFileStream }

procedure TProgressFileStream.InitProgressCounter(ASize: Int64);
begin
  FProcessed := 0;
  if ASize <= 0 then
    FSize := 1
  else
    FSize := ASize;
  if Assigned(FOnProgress) then
    FOnProgress(Self, 0);
end;

function TProgressFileStream.Read(var Buffer; Count: Integer): Integer;
begin
  Result := inherited Read(Buffer, Count);
  Inc(FProcessed, Result);
  if Assigned(FOnProgress) then
    FOnProgress(Self, FProcessed / FSize);
end;

function TProgressFileStream.Write(const Buffer; Count: Integer): Integer;
begin
  Result := inherited Write(Buffer, Count);
  Inc(FProcessed, Result);
  if Assigned(FOnProgress) then
    FOnProgress(Self, FProcessed / FSize);
end;

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
var
  Stream: TProgressFileStream;
begin
  ADOQuery1.Open;
  Stream := TProgressFileStream.Create('H:\Delphi\Blobtest.docx', fmOpenRead);
  try
    Stream.OnProgress := StreamProgress;
    Stream.InitProgressCounter(Stream.Size);
    ADOQuery1.Append;
    ADOQuery1Blob.LoadFromStream(Stream);
    ADOQuery1.Post;
  finally
    Stream.Free;
  end;
  Stream := TProgressFileStream.Create('H:\Delphi\Blobtest2.docx', fmCreate);
  try
    ADOQuery1.Last;
    Stream.OnProgress := StreamProgress;
    Stream.InitProgressCounter(ADOQuery1Blob.BlobSize);
    ADOQuery1Blob.SaveToStream(Stream);
  finally
    Stream.Free;
  end;
end;

procedure TForm1.StreamProgress(Sender: TObject; Percentage: Single);
begin
  ProgressBar.Position := Round(Percentage * ProgressBar.Max);
end;

end.

Although this OnProgress event is implemented on the file-side of the process, the actual progress that it represents is the overall process, including database communication.