Delphi delete FireMonkey element from Form on Android - delphi

Question

I created an element on my Form with this code in the OnShow event:
procedure TForm4.FormShow(Sender: TObject);
var
VertScrollLink:TVertScrollBox;
begin
VertScrollLink := TVertScrollBox.Create(form4);
VertScrollLink.Align := TAlignLayout.Client;
VertScrollLink.Parent := form4;
end;
On some action, I need to delete the layout dynamically:
for LIndex := form4.ComponentCount-1 downto 0 do
begin
if (form4.Components[LIndex].ToString='TVertScrollBox') then
begin
//showmessage(form4.Components[LIndex].ToString);
form4.Components[LIndex].Free;
end;
end;
This code works good on Windows, but does not delete anything on Android.

Answer 1

The reason is because Delphi uses Automatic Reference Counting for Objects on mobile platforms (iOS and Android), but not on desktop platforms (Windows and OSX). Your Free() is effectively a no-op, because accessing the component from the Components[] property will increment its reference count, and then the Free() will decrement it (in fact, the compiler should have issued a warning about the code having no effect). The component still has active references to it (its Owner and Parent), so it is not actually freed.
If you want to force the component to be freed, you need to call DisposeOf() on it, eg:
for LIndex := form4.ComponentCount-1 downto 0 do
begin
if form4.Components[LIndex] is TVertScrollBox then
begin
form4.Components[LIndex].DisposeOf;
end;
end;
Alternatively, remove the active references and let ARC handle the destruction normally:
var
VertScrollLink: TVertScrollBox;
LIndex: Integer;
begin
...
for LIndex := form4.ComponentCount-1 downto 0 do
begin
if form4.Components[LIndex] is TVertScrollBox then
begin
VertScrollLink := TVertScrollBox(form4.Components[LIndex]);
VertScrollLink.Parent := nil;
VertScrollLink.Owner.RemoveComponent(VertScrollLink);
VertScrollLink := nil;
end;
end;
...
end;
That being said, you might consider keeping track of the component you create so you don't need to use a loop to find it later:
type
TForm4 = class(TForm)
procedure FormShow(Sender: TObject);
...
private
VertScrollLink: TVertScrollBox;
...
end;
procedure TForm4.FormShow(Sender: TObject);
begin
VertScrollLink := TVertScrollBox.Create(Self);
VertScrollLink.Align := TAlignLayout.Client;
VertScrollLink.Parent := Self;
end;
begin
...
if Assigned(VertScrollLink) then
begin
VertScrollLink.DisposeOf;
{ or:
VertScrollLink.Parent := nil;
VertScrollLink.Owner.RemoveComponent(VertScrollLink);
}
VertScrollLink := nil;
end;
...
end;