Re: EAccess violation when try to remove object for
Tlistobject

On Tue, 11 Dec 2007 11:47:50 +0200, Stanislav Nedelchev wrote:

> For example I test it with method Extract
> FForms.Extract(TfBuddyForm(FForms[i]));
> 
> and it's never crahs but it's not free memory.

It sounds like it has nothing to do with the list, but that something
happens when you Free the form (i.e. some code in the destructor an
error in a component, etc.)

What happens if you do:
  TfBuddyForm(FForms[i]).Free;
And ignore the list for the moment?  

By the way this group is for discussing object orientated design, if
you choose an appropriate group you will get better answers.

-- 
Marc Rohloff [TeamB]

TObjectList has two creation methods. The default (FForms := 
TObjectList.Create;) creates a list of objects, forms in your case, and 
destroy them when you do a "Remove".

If you just want to remove the reference to the forms in the list, and 
leave the forms in memory, you should create the TObjectList this way:

FForms := TObjectList.Create(False);

The parameter tells the list it doesn't own the forms, but only a 
reference to them, if you use "True" as parameter, the list will
destroy 
de forms when you call Delete, Remove or Free.

 From Delphi 7 help:

"Description
Create creates a TObjectList instance. If no parameter is specified, or 
if the constructor is called with AOwnsObjects set to true, the new 
TObjectList is initialized with OwnsObjects set to true."

I hope it helps.

Leonardo M. Ramé
http://leonardorame.blogspot.com


Stanislav Nedelchev escribió:
> For example I test it with method Extract
> FForms.Extract(TfBuddyForm(FForms[i]));
> 
> and it's never crahs but it's not free memory.
> 
> Regards.
> 
> Stanislav Nedelchev написа:
>> Hi to everybody I have problem when I try to remove object from
TobjectList.
>> FForms is TobjectList
>> TfBuddyForm is a Tform.
>> I can change caption if the form it's seams that this object exists
but
>> I can delete it. The most strange thng is that sometime it's not
crash.
>> I'm using Jedi VCL in this form . Can anybody give Idea what to look
to
>> fix this problem.
>>
>>
>> Here is the example code.
>>
>> function TMainForm.RemoveForm(BuddyName_: string): TfBuddyForm;
>> var
>>   i: integer;
>>   l: integer;
>> begin
>>   result := nil;
>>   i := 0;
>>   l:=0;
>>   BuddyName_ := lowercase(BuddyName_); //guarantee case insensitive
search
>>   while (result = nil) and (i < FForms.Count) do
>>   begin
>>     if lowercase(TfBuddyForm(FForms[i]).BuddyName) = BuddyName_ then
>>     begin
>>     result := TfBuddyForm(FForms[i]);
>>     Result.Caption := '------'; //Works
>>     FForms.Remove(TfBuddyForm(FForms[i])); //crash
>>     end
>>     else
>>     inc(i)
>>     end;
>>     {
>>     for l := lbForms.Items.Count - 1 downto 0 do
>>     if lbForms.Items.Strings[l] = BuddyName_  then
>>     lbForms.Items.Delete(l);
>>     }

Hi to everybody I have problem when I try to remove object from TobjectList.
FForms is TobjectList
TfBuddyForm is a Tform.
I can change caption if the form it's seams that this object exists but
I can delete it. The most strange thng is that sometime it's not crash.
I'm using Jedi VCL in this form . Can anybody give Idea what to look to
fix this problem.


Here is the example code.

function TMainForm.RemoveForm(BuddyName_: string): TfBuddyForm;
var
  i: integer;
  l: integer;
begin
  result := nil;
  i := 0;
  l:=0;
  BuddyName_ := lowercase(BuddyName_); //guarantee case insensitive search
  while (result = nil) and (i < FForms.Count) do
  begin
    if lowercase(TfBuddyForm(FForms[i]).BuddyName) = BuddyName_ then
    begin
    result := TfBuddyForm(FForms[i]);
    Result.Caption := '------'; //Works
    FForms.Remove(TfBuddyForm(FForms[i])); //crash
    end
    else
    inc(i)
    end;
    {
    for l := lbForms.Items.Count - 1 downto 0 do
    if lbForms.Items.Strings[l] = BuddyName_  then
    lbForms.Items.Delete(l);
    }

For example I test it with method Extract
FForms.Extract(TfBuddyForm(FForms[i]));

and it's never crahs but it's not free memory.

Regards.

Stanislav Nedelchev написа:
> Hi to everybody I have problem when I try to remove object from
TobjectList.
> FForms is TobjectList
> TfBuddyForm is a Tform.
> I can change caption if the form it's seams that this object exists but
> I can delete it. The most strange thng is that sometime it's not crash.
> I'm using Jedi VCL in this form . Can anybody give Idea what to look to
> fix this problem.
> 
> 
> Here is the example code.
> 
> function TMainForm.RemoveForm(BuddyName_: string): TfBuddyForm;
> var
>   i: integer;
>   l: integer;
> begin
>   result := nil;
>   i := 0;
>   l:=0;
>   BuddyName_ := lowercase(BuddyName_); //guarantee case insensitive search
>   while (result = nil) and (i < FForms.Count) do
>   begin
>     if lowercase(TfBuddyForm(FForms[i]).BuddyName) = BuddyName_ then
>     begin
>     result := TfBuddyForm(FForms[i]);
>     Result.Caption := '------'; //Works
>     FForms.Remove(TfBuddyForm(FForms[i])); //crash
>     end
>     else
>     inc(i)
>     end;
>     {
>     for l := lbForms.Items.Count - 1 downto 0 do
>     if lbForms.Items.Strings[l] = BuddyName_  then
>     lbForms.Items.Delete(l);
>     }

That's exactly why I think the problem is the TObjectList. When you 
remove an item from the list, and the list was created without 
Create(False), the form is Destroyed. If after that, you try to call 
Form.Free, an Access Violation is raised because the form wasn't there 
anymore.

Leonardo M. Ram�
http://leonardorame.blogspot.com


Marc Rohloff [TeamB] escribi�:
> On Tue, 11 Dec 2007 11:47:50 +0200, Stanislav Nedelchev wrote:
> 
>> For example I test it with method Extract
>> FForms.Extract(TfBuddyForm(FForms[i]));
>>
>> and it's never crahs but it's not free memory.
> 
> It sounds like it has nothing to do with the list, but that something
> happens when you Free the form (i.e. some code in the destructor an
> error in a component, etc.)
> 
> What happens if you do:
>   TfBuddyForm(FForms[i]).Free;
> And ignore the list for the moment?  
> 
> By the way this group is for discussing object orientated design, if
> you choose an appropriate group you will get better answers.