TListItem Objects - delphi

Question

I would like to program the following situation:
I have 2 different ListViews in a form. I would like to attach specific items from ListView2 into a ListView1 item. After the "Parent" Item gets deleted, it should also delete all the attached items from ListView2.
I tried this so far:
type
TITEMS = record
A_Items : array of TListItem;
end;
A Button that adds an item to ListView1 (ParentItems)
var
item : TListItem;
begin
item := ListView1.Items.Add;
item.Caption := 'ParentTestItem';
item.SubItems.Add('TestSubItem');
A button that adds an item to ListView2 (ChildItems)
var
item : TlistItem;
items : TITEMS;
begin
if ListView1.Selected = NIL then exit; // Make sure an item is selected.
item := ListView2.Items.Add;
item.Caption := 'ChildTestItem';
item.SubItems.Add('TestSubItem');
SetLength (items.item, Length(items.item) + 1); // wrong?
items.item[Length(items.item)-1] := item;
ListView1.Selected.SubItems.Objects[0] := #items;
A button that removes a ParentItem (and it should delete ChildItems as well...)
var
items : TItems;
i : Integer;
item : TlistItem;
begin
if ListView1.Selected = NIL then exit; // Make sure an item is selected.
items := TItems(ListView1.Selected.SubItems.Objects[0]); // Cast
for i := 0 to Length (items.item) - 1 do begin
item := items.item[i];
item.Delete;
end;
ListView1.Selected.Free;
Any Idea how I could realize this?

Answer 1

You need to allocate the list of items dynamically on the heap, not locally on the stack, so it stays valid in memory while you are using it.
I would suggest using a TList instead of an array, it is easier to allocate dynmically. I would also suggest using the TListItem.Data property instead of the TListItem.SubItems.Objects[] property (unless you are already using the Data property for something else).
procedure TForm1.AddParentBtnClick(Sender: TObject);
var
item : TListItem;
begin
item := ListView1.Items.Add;
item.Caption := 'ParentTestItem';
item.SubItems.Add('TestSubItem');
end;
procedure TForm1.AddChildBtnClick(Sender: TObject);
var
Selected, item : TListItem;
items : TList;
begin
Selected := ListView1.Selected;
if Selected = nil then Exit; // Make sure an item is selected.
items := TList(Selected.Data);
if items = nil then begin
items := TList.Create;
Selected.Data := items;
end;
item := ListView2.Items.Add;
try
item.Caption := 'ChildTestItem';
item.SubItems.Add('TestSubItem');
items.Add(item);
except
item.Delete;
raise;
end;
end;
procedure TForm1.DeleteParentBtnClick(Sender: TObject);
var
Selected : TListItem;
begin
Selected := ListView1.Selected;
if Selected <> nil then Selected.Delete;
end;
procedure TForm1.ListView1Deletion(Sender: TObject; Item: TListItem);
var
items : TList;
i : Integer;
begin
items := TList(Item.Data); // Cast
if items <> nil then begin
for i := 0 to items.Count - 1 do begin
TListItem(items[i]).Delete;
end;
items.Free;
Item.Data := nil;
end;
end;