How to use classes and forms together

[nikel]

Hello, I'm trying to create and free my class. In the main lpr file I haver this code:

Code: Pascal  [Select][+][-]

1. {$R *.res}
2.  
3. begin
4.   RequireDerivedFormResource:=True;
5.   Application.Scaled:=True;
6.   Application.Initialize;
7.   // Application.CreateForm(TForm1, Form1);
8.  
9.   D:=TDownload.Create(nil);
10.   D.DoRun;
11.  
12.   Application.Run;
13.  
14.   D.Free;
15. end.

It never reaches D.Free when I debug my program. I tried to place the line to different places however it caused other problems. How can use forms and classes together?

Modify:

Here's how I declare my class:

Code: Pascal  [Select][+][-]

1.   TDownload = class(TForm1)
2.   private
3.     LinkToFile    : string;
4.     TaskToKill    : shortstring;
5.   public
6.     constructor Create(AOwner: TComponent); reintroduce;
7.     constructor Create(AOwner: TComponent; L: string; T: shortstring); reintroduce;
8.     destructor Destroy; override;
9.  
10.     procedure SetLinkToFile(L: string);
11.     function GetLinkToFile(): string;
12.     ...

[ASerge]

It never reaches D.Free when I debug my program. I tried to place the line to different places however it caused other problems. How can use forms and classes together?

Comment out Application.Run or add Application.Terminate; before that.

[nikel]

Thanks for the reply. I tried commenting out Application.Run, this time the form didn't work correctly.

[ASerge]

Thanks for the reply. I tried commenting out Application.Run, this time the form didn't work correctly.

If you have a regular form, then why not just use:

Code: Pascal  [Select][+][-]

1. begin
2.   RequireDerivedFormResource:=True;
3.   Application.Scaled:=True;
4.   Application.Initialize;
5.   // Application.CreateForm(TForm1, Form1);
6.   Application.CreateForm(TDownload, D);
7.   Application.Run;
8. end.

[nikel]

ASerge, thanks again.  I fixed the problem with this:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Close_PnlMouseDown(Sender: TObject; Button: TMouseButton;
2.   Shift: TShiftState; X, Y: Integer);
3. begin
4.   with TPanel(Sender) do
5.   begin
6.     BevelOuter:=bvNone;
7.     BevelInner:=bvLowered;
8.   end;
9.  
10.   if not (D = nil) then
11.   begin
12.     D.Free;
13.   end;
14.   Application.Terminate;
15. end;

[ASerge]

The Free method does not nil the object reference.
Better:

Code: Pascal  [Select][+][-]

1. if Assigned(D) then
2.   FreeAndNil(D);

or even simple

Code: Pascal  [Select][+][-]

1. FreeAndNil(D);

[cdbc]

Hi
Caution with:

Code: Pascal  [Select][+][-]

1. FreeAndNil(D);

It will crash if 'D' is nil...!

Code: Pascal  [Select][+][-]

1. if Assigned(D) then FreeAndNil(D);

...is the safer bet 
Regards Benny

[ASerge]

It will crash if 'D' is nil...!

No. TObject(nil).Free; work fine.

[cdbc]

Hi
Yes, but that is not what you are doing!
'FreeAndNil' doesn't check for nil 
Free does.
Regards Benny

[ASerge]

Hi
Yes, but that is not what you are doing!
'FreeAndNil' doesn't check for nil 

FreeAndNil simply calls the Free method, which performs the check. And then sets the reference to nil. It is safe to call FreeAndNil with nil.