//创建时也要注意:frmMain为父窗体,Form1为子窗体
procedure TfrmMain.N1Click(Sender: TObject);
begin
if Form1=NIL then
Application.CreateForm(TForm1,Form1)
else
Form1.Show;
end;
procedure Form1.OnClose(Sender: TObject; var Action: TCloseAction);
begin
Form1:=NIL;
Action := caFree;
end;