Using FV's TListBox, Memory Leak,
lazarus / 65-FV-Textmode IDE

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gasensor · 2022-05-02 17:16

I am Using FV's TListBox. But find it Memory Leaked. It has been
bothering me for a long time.

sechshelme 's "FPC FreeVision Tutorial"  do not have a  TListBox
DEMO...

Can anyone give me an example of how to use TLISTBOX properly?

TKS

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Mathias · 2022-05-22 15:30

After trying back and forth for a long time, this unpleasant memory
corpse remains with TList.
I have described all the findings in my GitHub Issues channel.
https://github.com/sechshelme/Lazarus-FreeVision/issues/3

I tried out several components, where I created them and then released
them again with Dispose/Done.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i constructor
TMyDialog.Init;var  Rect: TRect;  ScrollBar: PScrollBar;  i:
Sw_Integer;  rad: PRadioButtons;  bp:PButton;const  Tage: array [0..6]
of shortstring = (    'Montag', 'Dienstag', 'Mittwoch', 'Donnerstag',
'Freitag', 'Samstag', 'Sonntag'); begin  Rect.Assign(10, 5, 67, 17); 
inherited Init(Rect, 'ListBox Demo');   rad := New(PRadioButtons,
Init(Rect, NewSItem('~G~ross', NewSItem('~M~ittel',
NewSItem('~K~lein', nil)))));  Dispose(rad, Done); // io.   bp :=
New(PButton, Init(Rect, '~T~ag', cmTag, bfNormal));  Dispose(bp,
Done); // io.  exit;
But if I do the same with PListBox, there are memory corpses.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   ListBox
:= new(PListBox, Init(Rect, 1, nil));  Dispose(ListBox, Done);  //
Memory Leak !  exit;


Could there be a bug in PListBox?

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Mathias · 2022-05-23 16:36

I took a closer look at the TFileListBox used by the TFileDialog. Then
I came across the following:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i destructor
TFileList.Done;begin  if List <> nil then Dispose(List, Done); 
TListBox.Done;end; They added their own destructor there.

Now I also built a new ListBox and added a destructor and used this
ListBox in my dialog.
As it seems, this works. the memory leak is gone.

I'll make a few more tries.
In my opinion, this is a bug in TListBox, which lacks the destructor.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type 
PNewListBox = ^TNewListBox;  TNewListBox = object(TListBox)   
destructor Done; virtual;  end;...destructor TNewListBox.Done;begin 
if List <> nil then begin    Dispose(List, Done);  end; 
TListBox.Done;end;constructor TMyDialog.Init;var  Rect: TRect; 
ScrollBar: PScrollBar;  i: Sw_Integer;const  Tage: array [0..6] of
shortstring = (    'Montag', 'Dienstag', 'Mittwoch', 'Donnerstag',
'Freitag', 'Samstag', 'Sonntag'); begin  Rect.Assign(10, 5, 67, 17); 
inherited Init(Rect, 'ListBox Demo');   // StringCollection 
StringCollection := new(PStringCollection, Init(5, 5));  for i := 0 to
Length(Tage) - 1 do begin   
StringCollection^.Insert(NewStr(Tage[i]));  end;   // ScrollBar für
ListBox  Rect.Assign(31, 2, 32, 7);  ScrollBar := new(PScrollBar,
Init(Rect));  Insert(ScrollBar);   // ListBox  Rect.Assign(5, 2, 31,
7);  ListBox := new(PNewListBox, Init(Rect, 1, ScrollBar)); 
ListBox^.NewList(StringCollection);  Insert(ListBox);   // Cancel-
Button  Rect.Assign(19, 9, 32, 10);  Insert(new(PButton, Init(Rect,
'~T~ag', cmTag, bfNormal)));   // Ok-Button  Rect.Assign(7, 9, 17,
10);  Insert(new(PButton, Init(Rect, '~O~K', cmOK, bfDefault)));end;

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Mathias · 2022-05-30 15:21

So, now a tutorial for ListBoxes has been added.
With the ListBoxes, you can manually remove the loaded list from
memory. This is described in the tutorial.