17/06/13
Synchronizing Threads and GUI in Delphi application
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Delphi Synchronizing Threads and GUI in Delphi application
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From Zarko Gajic, former About.com Guide C ode subm itte d by Je ns Borrisholt
Multi-threading in Delphi lets you create applications that include several simultaneous paths of execution. A "normal" Delphi application is single-threaded: all (VCL) objects access their properties and execute their methods within this single thread. Threads and GUI To speed up data processing in your application you can decide to include one or more "secondary" threads.
Synchronizing Thre ads and GUI
When several threads are running in the application a question arises: how to update your GUI (user interface) as a result of a thread execution. The question lies in the TThread class Synchronize method. To update your application's user interface - main thread - from a secondary thread you need to call the Synchronize method - a thread-safe method that avoids multi-threading conflicts that can arise from accessing object properties or methods that are not thread-safe, or using resources not in the main thread of execution. An example demo uses several buttons with progress bar, each progress bar displaying the current "state" of the thread execution... Download source code unit MainU; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, ComCtrls, StdCtrls, ExtCtrls; type //interceptor class TButton = class(StdCtrls.TButton) OwnedThread: TThread; ProgressBar: TProgressBar; end; TMyThread = class(TThread) private FCounter: Integer; FCountTo: Integer; FProgressBar: TProgressBar; FOwnerButton: TButton; procedure DoProgress; procedure SetCountTo(const Value: Integer) ; procedure SetProgressBar(const Value: TProgressBar) ; procedure SetOwnerButton(const Value: TButton) ; protected procedure Execute; override; public constructor Create(CreateSuspended: Boolean) ; property CountTo: Integer read FCountTo write SetCountTo; property ProgressBar: TProgressBar read FProgressBar write SetProgressBar; property OwnerButton: TButton read FOwnerButton write SetOwnerButton; end; TMainForm = class(TForm) Button1: TButton; ProgressBar1: TProgressBar; Button2: TButton;
delphi.about.com/od/kbthread/a/thread-gui.htm
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Synchronizing Threads and GUI in Delphi application ProgressBar2: TProgressBar; Button3: TButton; ProgressBar3: TProgressBar; Button4: TButton; ProgressBar4: TProgressBar; Button5: TButton; ProgressBar5: TProgressBar; procedure Button1Click(Sender: TObject) ; end; var MainForm: TMainForm; implementation {$R *.dfm} { TMyThread } constructor TMyThread.Create(CreateSuspended: Boolean) ; begin inherited; FCounter := 0; FCountTo := MAXINT; end; procedure TMyThread.DoProgress; var PctDone: Extended; begin PctDone := (FCounter / FCountTo) ; FProgressBar.Position := Round(FProgressBar.Step * PctDone) ; FOwnerButton.Caption := FormatFloat('0.00 %', PctDone * 100) ; end; procedure TMyThread.Execute; const Interval = 1000000; begin FreeOnTerminate := True; FProgressBar.Max := FCountTo div Interval; FProgressBar.Step := FProgressBar.Max; while FCounter < FCountTo do begin if FCounter mod Interval = 0 then Synchronize(DoProgress) ; Inc(FCounter) ; end; FOwnerButton.Caption := 'Start'; FOwnerButton.OwnedThread := nil; FProgressBar.Position := FProgressBar.Max; end; procedure TMyThread.SetCountTo(const Value: Integer) ; begin FCountTo := Value; end; procedure TMyThread.SetOwnerButton(const Value: TButton) ; begin FOwnerButton := Value; end; procedure TMyThread.SetProgressBar(const Value: TProgressBar) ; begin FProgressBar := Value; end; procedure TMainForm.Button1Click(Sender: TObject) ; var aButton: TButton; aThread: TMyThread; aProgressBar: TProgressBar; begin aButton := TButton(Sender) ; if not Assigned(aButton.OwnedThread) then begin
delphi.about.com/od/kbthread/a/thread-gui.htm
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Synchronizing Threads and GUI in Delphi application aThread := TMyThread.Create(True) ; aButton.OwnedThread := aThread; aProgressBar := TProgressBar(FindComponent(StringReplace(aButton.Name, 'Button', 'ProgressBar', []))) ; aThread.ProgressBar := aProgressBar; aThread.OwnerButton := aButton; aThread.Resume; aButton.Caption := 'Pause'; end else begin if aButton.OwnedThread.Suspended then aButton.OwnedThread.Resume else aButton.OwnedThread.Suspend; aButton.Caption := 'Run'; end; end; end.
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