TSringList Question

[JLWest]

Can you Declare a Global TStringList simular to a Global Dynamic array.

I tried to do it the same way but an Access error when I tried to to do TList.Clear;

Code: Pascal  [Select][+][-]

1. Const
2.   BaseLeft = 25;    
3.  
4. Var
5.  TList: TStringList;
6.  
7. procedure TForm1.FormCreate(Sender: TObject);
8.  begin
9.   TList := TStringList.Create;
10. end;  
11.  
12. procedure TForm1.DoSomething;
13. begin
14.  TList.Clear;                                 // Access Violation
15. end;                            

[dseligo]

You can.
Try to change name, like below. TList is a class defined in 'classes'.

Code: Pascal  [Select][+][-]

1. Var
2.   List: TStringList;
3.  
4. procedure TForm1.FormCreate(Sender: TObject);
5. begin
6.   List := TStringList.Create;
7. end;  
8.  
9. procedure TForm1.DoSomething;
10. begin
11.   List.Clear;
12. end;

[PascalDragon]

Can you Declare a Global TStringList simular to a Global Dynamic array.

I tried to do it the same way but an Access error when I tried to to do TList.Clear;

You should instantiate a global variable in the initialization-section of the unit (and free it in the finalization-section) as otherwise it might be instantiated multiple times if TForm1 is created multiple times. Also this way you can be sure that it's indeed initialized once TForm1.DoSomething runs.

[JLWest]

@PascalDragon Some of us are just Geico's.

It is nice to know it can be do but the answer is above my pay grade.

Never heard of the initialization-section or finalization-section.

[rvk]

Don't forget to do List.Free in FormDestroy if you create it in FormCreate.
Otherwise you get a memory leak.

And this code is indeed only safe when there is only one TForm1 created (because a second TForm1 would overwrite the first List instance). To fix that you could also move the List var definition to within the TForm1 class.

[winni]

@PascalDragon Some of us are just Geico's.

It is nice to know it can be do but the answer is above my pay grade.

Never heard of the initialization-section or finalization-section.

Hi!

Code: Pascal  [Select][+][-]

1. unit  Whatever;
2. ...
3. Var  List: TStringList;
4. ...
5.  
6. Procedure ClearList;
7. begin
8. List.clear;
9. end;
10.  
11. ...
12.  
13. initialization
14. List := TStringList.create;
15.  
16. finalization
17. List.free;
18. end.
19.  

Read Marco Cantu for further infos.

https://www.marcocantu.com/epascal/English/ch11unit.htm

Winni

[JLWest]

Hi Wini

Can I assume that the initialization and  finalization can go anywhere after the implementation 

Thanks

[rvk]

Can I assume that the initialization and  finalization can go anywhere after the implementation 

No, they need to be directly above the "end." of the unit, so completely at the end.

[PascalDragon]

@PascalDragon Some of us are just Geico's.

It is nice to know it can be do but the answer is above my pay grade.

Never heard of the initialization-section or finalization-section.

It might pay of to take a look at the documentation then.