How to update progress indicator from a second thread? - delphi

Question

I have a main form with a progress indicator on it.
In the datamodule I've ten datasets, each of them has an OnBeforeOpen event defined.
I would like to show through the progress bar in the main form a percentage of progress of the opened datasets.
Since I'm completely new to multithreading programming, can someone please give me some advice?
Thank you very much

Answer 1

Either post a message from the thread to the main thread and update the progress bar from there or use the TThread.Queue method to execute some code in the context of the main thread.
unit Unit12;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ComCtrls;
const
WM_UPDATE_PB = WM_USER;
type
TForm12 = class(TForm)
ProgressBar1: TProgressBar;
ProgressBar2: TProgressBar;
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
public
procedure WMUpdatePB(var msg: TMessage); message WM_UPDATE_PB;
end;
var
Form12: TForm12;
implementation
{$R *.dfm}
procedure UpdateFromThreadViaMessage;
var
i: integer;
begin
for i := 1 to 100 do begin
Sleep(20);
PostMessage(Form12.Handle, WM_UPDATE_PB, i, 0);
end;
end;
procedure UpdateFromThreadViaQueue;
var
i: integer;
begin
for i := 1 to 100 do begin
Sleep(20);
TThread.Queue(nil,
procedure begin
Form12.ProgressBar2.Position := i;
end);
end;
end;
procedure TForm12.Button1Click(Sender: TObject);
begin
TThread.CreateAnonymousThread(UpdateFromThreadViaMessage).Start;
TThread.CreateAnonymousThread(UpdateFromThreadViaQueue).Start;
end;
procedure TForm12.WMUpdatePB(var msg: TMessage);
begin
ProgressBar1.Position := msg.WParam;
end;
end.