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How to perform regular screen refresh while processing?

Posted on 2008-10-26
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Last Modified: 2012-05-05
Hi

my application is processing data and it can take up to 10 minutes to do. It can make tens of millions of cycles... to have some sort of screen refresh and indicator I put this to every main procedure :

if counter mod 10000 then
begin
    StatusForm.Show;
    StatusForm.myLabel.Caption := 'Procesing #'+myIndicatorNo;
    Application.ProcessMessages;
end;


Now, this works OK. Obivously with 'IF' I make sure that refresh doesn't take too much of resources, because it CAN, at least in my application!

Now, I would like to have another, easier and much less code approach. So I was thinking of having a Timer that would do the same think every second.

Is this possible? Can Timer take a lot of resources, while waiting for 1 sec to pass? Is this, being executed on Timer event, actually possible in one-threaded application?

If this is possible for my application, please give me some pointers.

Thank you

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Question by:Delphi_developer
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16 Comments
 
LVL 31

Expert Comment

by:moorhouselondon
ID: 22808545
I would have thought that Timer is interrupt driven, and therefore uses less resources, but others here will have a clearer idea.
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LVL 37

Expert Comment

by:Geert Gruwez
ID: 22808700
nope, not in 1 threaded app

the timer event will be put on the queue, and wait for the thread to process it
which off course will never happen as your calculation routine is using the 1 thread

you really need to put the calculation routine in a thread
if you want the GUI not to freeze
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LVL 31

Expert Comment

by:moorhouselondon
ID: 22808733
I for one would be interested to know how to implement that
0
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LVL 37

Accepted Solution

by:
Geert Gruwez earned 500 total points
ID: 22810346
well if is only 1 routine just put it in the
procedure Execute of a thread

I even wrote a Thread type for this, from which you can callback the progress

type
 
  TCallbackProc = procedure (aMessage: string; aMessageInfo: Integer = 0) of object;
 
  TCallbackThread = class(TThread)
  private
    FCallBack: TCallbackProc;
    FCallbackMsg: string;
    FCallbackMsgInfo: integer;
    procedure SynchedCallback;
  protected
    procedure DoCallback(aMsg: string; aMsgInfo: integer = 0); virtual;
    property Callback: TCallbackProc read FCallback;
  public
    constructor Create(aCallback: TCallbackProc; CreateSuspended: Boolean = False); reintroduce; virtual;
  end;
 
{ TCallbackThread }
 
constructor TCallbackThread.Create(aCallback: TCallbackProc; CreateSuspended: Boolean = False);
begin
  inherited Create(CreateSuspended);
  FreeOnTerminate := True;
  FCallback := aCallback;
end;
 
procedure TCallbackThread.DoCallback(aMsg: string; aMsgInfo: Integer = 0);
begin
  FCallbackMsg := aMsg;
  FCallbackMsgInfo := aMsgInfo;
  Synchronize(SynchedCallback);
end;
 
procedure TCallbackThread.SynchedCallback;
begin
  if Assigned(FCallback) then
    FCallBack(FCallbackMsg, FCallbackMsgInfo);
end;

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LVL 37

Expert Comment

by:Geert Gruwez
ID: 22810347
Example of DB reading records

procedure TMyThread.Execute;
var I: Integer;
begin
  DoCallback('Thread started', 0);
 
  DoCallback('Records ' + IntToStr(Query.RecordCount)), 1);
  I := 0;
  while not Query.Eof do 
  begin
    Inc(I);
    DoCallback('Handling record ' + IntToStr(I), 2);
    Query.Next;
  end;
 
  DoCallback('Thread started', 0);
end;

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LVL 37

Expert Comment

by:Geert Gruwez
ID: 22810366
in your Form create a thread with the callback proc assigned


type
  TForm1 = class(TForm)
    ProgressBar1: TProgressBar;
    Panel1:  TPanel;
  private
    fThread: TMyThread;
    procedure ProgressUpdate(aMessage: string; aMessageInfo: Integer = 0);
  end;
 
procedure TForm1.ProgressUpdate(aMessage: string; aMessageInfo: Integer = 0);
begin
  Panel1.Caption := aMessage;
  case aMessageInfo of
    0: ProgressBar1.Position := 0;
    1: 
    begin
      ProgressBar1.Position := 0;
      ProgressBar1.Max := StrToInt(Copy(aMessage, 8, Length(aMessage)));
    end;
    2: ProgressBar1.Position := ProgressBar1.Position + 1;
    3: 
    begin
      ProgressBar1.Position := ProgressBar1.Max;
      fThread := nil;
    end;
  end;
end;
 
procedure TForm1.Button1Click(Sender: Object);
begin
  if not Assigned(fThread) then 
    fThread := TMyThread.Create(ProgressUpdate);
end;

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LVL 37

Expert Comment

by:Geert Gruwez
ID: 22810388
o yes,
no need to call
Application.ProcessMessages
0
 
LVL 31

Expert Comment

by:moorhouselondon
ID: 22810626
GG:

v. comprehensive ty.  I hope it answers DD's q!
0
 

Author Comment

by:Delphi_developer
ID: 22829566
@Geert Gruwez: Thank you! I will need some time to test if this can be applied to my app...
0
 

Author Closing Comment

by:Delphi_developer
ID: 31514375
I decided that running my app in threads is a little too complicated... too many errors and too much things still to learn about threads, for now.

But thank you for the solution, I will definately use it in another app.

I will go back to  Application.ProcessMessages; for now, it is the easiset way and it works 100% for my app.

Thank you
0
 
LVL 37

Expert Comment

by:Geert Gruwez
ID: 22907584
Please read the Help about giving grades for answers.
If someone gives you an excellent approach then the answer deserves an A
The questioner deserves a B for not implementing it.
And not vice versa
0
 

Author Comment

by:Delphi_developer
ID: 22907626
Sorry, I thought C is for not using the proposed solution and A for it to be a solution to the question. So, I gave B because it is a good solutions, but not gonna use it as a solutinos for my question... I see I messed up.

0
 
LVL 37

Expert Comment

by:Geert Gruwez
ID: 22909583
nobody's perfect :)
0
 
LVL 37

Expert Comment

by:Geert Gruwez
ID: 22973718
>>But thank you for the solution, I will definately use it in another app.

don't you think you should change the grade to an A since you are going to use the solution ?
0
 
LVL 1

Expert Comment

by:Vee_Mod
ID: 22974940
Grade change by Asker request.

Vee_Mod
Experts Exchange Moderator
0
 

Author Comment

by:Delphi_developer
ID: 22974960
@Geert_Gruwez: thank you for pointing this out - I didn't know I can do this, until your comment and a quick browse through the Help

@Vee_Mod: Thank you.
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