How do I interrupt a thread?: delphi, interrupt, form2, thread

How do I interrupt a thread?

This should be simple... But I cannot get it to work.

This is in Delphi 7 - I've got 2 units, unit1 & unit2 with form1 and form2. Form1 has a single button 'Start'. Form2 has a progress bar and a button 'Cancel'.

Unit1.pas
procedure TForm1.StartClick(Sender: TObject);
var
i : integer;
begin
Form2.Show;
for i := 1 to 1000000 do
begin
Form2.ProgressBar1.Position := Form2.ProgressBar1.Position + 1;
Form2.Update;
end;
end;

Unit2.pas
procedure TForm2.CancelClick(Sender: TObject);
begin
Form2.Close;
end;

This is a very simplified example of what I have in my application - on running, Form1 shows - the Start button is clicked which starts a lengthy routine where I need to show the progress - so I show Form2 with a progress bar. What I want to do is be able to give the users the option of cancelling the routine by clicking on the cancel button on Form2. Trouble is that despite Form2 having focus it receives no events - specifically the CancelClick event never gets activated and so I can never escape from the routine.

How do I impliment this correctly? Thanks.

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You need you application to ProcessMessages during your long process.

procedure TForm1.Button1Click(Sender: TObject);
var
i: integer;
begin
Form2.Show;
Form2.Canceled := False;
for i := 1 to 1000000 do
begin
if Form2.Canceled then
Exit;
Form2.ProgressBar1.Position := Form2.ProgressBar1.Position + 1;
Form2.Update;
Application.ProcessMessages;
end;

procedure TForm2.Button1Click(Sender: TObject);
begin
Canceled := True;
Form2.Close;
end;

Another way to do this would be to put your long process in an actual thread. Like so:

unit Unit3;

interface

uses
Classes;

type
TLongProcess = class(TThread)
private
{ Private declarations }
protected
procedure Execute; override;
procedure UpdatePosition;
end;

implementation

{ Important: Methods and properties of objects in visual components can only be
used in a method called using Synchronize, for example,

Synchronize(UpdateCaption);

and UpdateCaption could look like,

procedure TLongProcess.UpdateCaption;
begin
Form1.Caption := 'Updated in a thread';
end; }

{ TLongProcess }

uses Unit2;

procedure TLongProcess.Execute;
var
i: Integer;
begin
for i := 1 to 1000000 do
begin
if Terminated then
Exit;
Synchronize(UpdatePosition);
end;
end;

procedure TLongProcess.UpdatePosition;
begin
Form2.ProgressBar1.Position := Form2.ProgressBar1.Position + 1;
Form2.Update;
end;

end.

-----------------------------------------

procedure TForm2.Button1Click(Sender: TObject);
begin
LongProcess.Terminate;
Form2.Close;
end;

procedure TForm2.FormShow(Sender: TObject);
begin
LongProcess := TLongProcess.Create(True);
LongProcess.FreeOnTerminate := True;
LongProcess.Resume;
end;

---------------------------------------------------

procedure TForm1.Button1Click(Sender: TObject);
begin
Form2.Show;
end;

Question

How do I interrupt a thread?

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delphi

interrupt

form2

thread

Delphi Programming

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