[Solved] StringGrid, a cell with a deleted TObject gives an access violation.

[Hansvb]

Hi,

In a stringgrid, I add an Object with some data to each cell. If I click on a cell with data, the contents of the object is shown in a TEdit. If I then delete the contents of the cell, I also remove the object of this cell. At least that is the intention. When I then click on the cell from which the object was removed, I get an error (access violation). I have put in a simplified project which reproduces this.
If you click on a cell with the right mouse button you get a popup with "Delete". If you click on this, the cell will be deleted and the object will be deleted. If you then click on the empty cell again, you will get an access violation.

Is my check if there is an object attached to the cell wrong? Or is deleting the object wrong?

[bytebites]

There is dangling pointer after dispose and it needs to be cleared

Code: Pascal  [Select][+][-]

1. StringGrid1.Objects[aCol,aRow]:=nil;

[Zvoni]

Code: Pascal  [Select][+][-]

1. procedure TForm1.MenuItem1Click(Sender: TObject);
2. begin
3.   StringGrid1.Cells[FCol, FRow]:= '';
4.  
5.   Dispose(PtrI]"]>Blockedbject(StringGrid1.Objects[FCol,FRow]));
6.   StringGrid1.Objects[FCol,FRow]:=Nil;  //<-- HERE
7. end;          
8.  
9. procedure TForm1.StringGrid1SelectCell(Sender: TObject; aCol, aRow: Integer;
10.   var CanSelect: Boolean);
11. var
12.   p: PtrI]"]>Blockedbject;
13. begin
14.   FCol:= aCol; // Used with Delete.
15.   FRow:= aRow; // Used with Delete.
16.  
17.  if PtrI]"]>Blockedbject(StringGrid1.Objects[acol,aRow]) <> nil then begin
18.     p := PtrI]"]>Blockedbject(StringGrid1.Objects[acol,aRow]);  // <<------ this goes wrong when the object is deleted.
19.     Edit1.Text:= p^.Name; // <-- access violation when delete is used.
20.   Else
21.     Edit1.Text:='';
22.   end;                
23. end;                              
24.  
25.  
26.  

Yes, you dispose of the Data, but it doesn't "nil" the Pointer of Objects[Fcol,Frow]

EDIT: Bytebites beat me to it

EDIT: There is something weird with the Forum and your var-name "PtrI]"]>Blockedbject"...

Testing

PtrI]"]>Blockedbject

[cdbc]

Hi Zvoni
That's just the forum blocking the word ']"]>Blocked', but shouldn't that be ']"]>Blocked'?!?

HAHAHA...  Gotcha - said the forum to the stupid Benny 

the word is ofc.: 'ttt eee mmm OOO' and the 2.nd 'TTT eee mmm uuu', let's see if that flies... 
edit2: Apparently them chinese tradesmen are quite invasive...
Regards Benny

[Zvoni]

Hi Zvoni
That's just the forum blocking the word ']"]>Blocked', but shouldn't that be ']"]>Blocked'?!?

HAHAHA...  Gotcha - said the forum to the stupid Benny 

the word is ofc.: 'ttt eee mmm OOO' and the 2.nd 'TTT eee mmm uuu', let's see if that flies... 
edit2: Apparently them chinese tradesmen are quite invasive...
Regards Benny

You gotta be shitting me.... seriously?!?!??!

[cdbc]

Hi Zvoni
Nooo mate, I shit you not... The block is quite efficient too =^
Regards Benny

[Zvoni]

Hi Zvoni
Nooo mate, I shit you not... The block is quite efficient too =^
Regards Benny

What's next?
AliBaba and EBay?

[cdbc]

Hi
Probably, or maybe even 'ChatGPT' 
Regards Benny

[Hansvb]

I wanted to write: I've completely lost you all.
But in the preview i see what you mean. The forum changes the var name automatically. Verry strange.

[cdbc]

Hi Hans
Yup, so now we have to call it "PtrI_t_e_m_Object", to not have the forum translate even our code-snippets... 
Yeah... Yippee \o/ 
Regards Benny

[Hansvb]

Thanks, I had indeed forgotten to remove the pointer.