How to release Objects stored in a TreeView from memory? - object

Question

I use Delphi 7. I create a record that stores info, and using pointers I store that record as an object in a TreeView with more than 100 items.
My problem is, how to release or eliminate all these objects from memory?
type
PMyRec = ^TMyRec;
TMyRec = record
Tipo: string;
parent: string;
end;
var
MyRecPtr: PMyRec;
for x := 1 to 100 do
begin
New(MyRecPtr);
MyRecPtr^.Tipo := '1';
MyRecPtr^.parent := 'paul';
Tree1.Items.AddChildObject(nil, IntToStr(x) + '-NewItem', MyRecPtr);
ListaDePonteiros.Add( MyRecPtr ); // I use a TList to store pointers
ListaDeObjectos.Add( MyRecPtr ); // I use a TList to store Objects
end;
How I try to delete them all:
procedure TForm1.Button2Click(Sender: TObject);
procedure EmptyTList(Var AList: TList);
var
intContador: integer;
begin
for intContador := (AList.Count-1) downto 0 do
begin
if Assigned(AList.Items[intContador]) then
begin
Dispose(AList.Items[intContador]);
AList.Items[intContador] := nil;
AList.Delete(intContador);
end;
end;
end;
begin
if Assigned(MyRecPtr) then
begin
EmptyTList(ListaDePonteiros);
end;
end;
When I delete all items in the TreeView OnDelete event, I have this:
if assigned(Node.Data) then
begin
Dispose(Node.Data);
end;
What I want to do is release all objects from memory!
If I dispose all objects using that list then if I delete any item from the TreeView an invalid pointer error is raised!!
Even with all pointers disposed, MyRecPtr still points to somewhere in memory, and Node.Data too!

Answer 1

Your code is crashing because you are freeing the same memory twice, because you have not defined any clear ownership of your record instances.
Your ListaDePonteiros and ListaDeObjectos lists are redundant and can be removed. The TTreeView can be the owner of the records and you can simply Dispose() of them in the TTreeView.OnDeletion event and be done with it 1.
var
MyRecPtr: PMyRec;
for x := 1 to 100 do
begin
New(MyRecPtr);
try
MyRecPtr^.Tipo := '1';
MyRecPtr^.parent := 'paul';
Tree1.Items.AddChildObject(nil, IntToStr(x) + '-NewItem', MyRecPtr);
except
Dispose(MyRecPtr);
raise;
end;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
Tree1.Items.Clear;
end;
procedure TForm1.Tree1Deletion(Sender: TObject; Node: TTreeNode);
begin
if Assigned(Node.Data) then
Dispose(PMyRec(Node.Data));
end;
Otherwise, if you choose to keep a separate list, keep the ListaDeObjectos list and remove the ListaDePonteiros list (as there is no reason to maintain 2 lists tracking the exact same values). You would just need to decide whether you want ListaDeObjectos or Tree1 to own the records you allocate:
If ListaDeObjectos is to be the owner, DO NOT call Dispose(Node.Data) in the TTreeView.OnDeletion event.
var
MyRecPtr: PMyRec;
Idx: Integer;
for x := 1 to 100 do
begin
New(MyRecPtr);
try
MyRecPtr^.Tipo := '1';
MyRecPtr^.parent := 'paul';
Idx := ListaDeObjectos.Add(MyRecPtr);
try
Tree1.Items.AddChildObject(nil, IntToStr(x) + '-NewItem', MyRecPtr);
except
ListaDeObjectos.Delete(Idx);
raise;
end;
except
Dispose(MyRecPtr);
end;
end;
procedure TForm1.Button2Click(Sender: TObject);
procedure EmptyTList(AList: TList);
var
intContador: integer;
begin
for intContador := 0 to (AList.Count-1) do
Dispose(PMyRec(AList[intContador]));
AList.Clear;
end;
begin
Tree1.Items.Clear;
EmptyTList(ListaDePonteiros);
end;
If Tree1 is to be the owner, DO NOT call Dispose(AList.Items[intContador]) in EmptyTList() (in fact, you can get rid of EmptyTList() altogether and just call ListaDeObjectos.Clear() when needed).
var
MyRecPtr: PMyRec;
Node: TNode;
for x := 1 to 100 do
begin
New(MyRecPtr);
try
MyRecPtr^.Tipo := '1';
MyRecPtr^.parent := 'paul';
Node := Tree1.Items.AddChildObject(nil, IntToStr(x) + '-NewItem', MyRecPtr);
except
Dispose(MyRecPtr);
raise;
end;
try
ListaDePonteiros.Add(MyRecPtr);
except
Node.Free;
raise;
end;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
ListaDePonteiros.Clear;
Tree1.Items.Clear;
end;
procedure TForm1.Tree1Deletion(Sender: TObject; Node: TNode);
begin
if Assigned(Node.Data) then
Dispose(PMyRec(Node.Data));
end;
Either way, when not mass-clearing Tree1 and ListaDeObjectos in one go, consider calling ListaDeObjectos.Remove() in the TTreeView.OnDeletion event to keep Tree1 and ListaDeObjectos in sync when removing individual nodes:
procedure TForm1.Tree1Deletion(Sender: TObject; Node: TNode);
begin
if Assigned(Node.Data) then
begin
// only if the TreeView is the owner...
Dispose(PMyRec(Node.Data));
ListaDeObjectos.Remove(Node.Data);
end;
end;
1. Whenever you do Dispose() your record instance, make sure you type-cast raw pointers to PMyRec or else the compiler will not finalize the record's members correctly, leaking memory.