How to correctly free a DragObject - delphi

Question

I got a memory leak error after drag & drop.
TMyDragObject = class(TDragObject)
public
MyInfo : string;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
System.ReportMemoryLeaksOnShutdown := True;
Button1.DragMode := dmAutomatic;
end;
procedure TForm1.Button1StartDrag(Sender: TObject; var DragObject: TDragObject);
begin
DragObject := TMyDragObject.Create;
TMyDragObject(DragObject).MyInfo := 'hi!';
end;
Where should DragObject be freed?
Thanks to all.

Answer 1

Free the object in the OnDragDrop handler for the control accepting the drop. Here's the event for a TMemo:
procedure TForm4.Memo1DragDrop(Sender, Source: TObject; X, Y: Integer);
begin
if IsDragObject(Source) then
begin
Memo1.Lines.Add(TMyDragObject(Source).MyInfo);
Source.Free;
end;
end;
Here's a more complete (and very trivial) example. Drop a TButton and TMemo on the form, set Button1.DragMode to dmAutomatic, add the variable Ctr: Integer to the form's private section, and wire up the event handlers; it allows you to drag the button into the memo, adding the text Item + the current value of Ctr to the memo's lines.
type
TMyDragObject=class(TDragObject)
Info: string;
end;
procedure TForm4.Button1StartDrag(Sender: TObject; var DragObject: TDragObject);
begin
Inc(Ctr);
DragObject := TMyDragObject.Create;
TMyDragObject(DragObject).Info := 'Item ' + IntToStr(Ctr);
end;
procedure TForm4.Memo1DragDrop(Sender, Source: TObject; X, Y: Integer);
begin
if IsDragObject(Source) then
begin
Memo1.Lines.Add(TMyDragObject(Source).Info);
Source.Free;
end;
end;
procedure TForm4.Memo1DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
begin
Accept := IsDragObject(Source);
end;
As an alternative, inherit from TDragObjectEx, which is automatically freed at the end of the drop operation, according to the documentation.
Note: TDragObject is not automatically freed at the end of a drag
operation. To work with a drag object that is freed at the end of the
drag operation, use TDragObjectEx instead