窗体控制问题！

Question

试试:
if not assigned(form2) then
  form2:=tform2.create(nil);

Answer 1

  Form2:=TForm2.Create(self);
  Form2.Show;
  Form2.Free;

Answer 2

  Form2:=TForm2.Create(self);
  Form2.ShowModal;
  Form2.Free;

Answer 3

Form2.free;
Form2:=nil;
if not assigned(Form2) then
 begin
  Form2:=Form2.Create(application);
  Form2.Show;
 end;

Answer 4

implementationuses unit2;{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
  if Form2=nil then
     Form2:=TForm2.Create(self); //self,application,nil都行
  Form2.Show;//记住:如果程序中有Form2.Free或者是在Form2的ONClose事件中用了
             //Action:=caFree,则一定要加Form2:=nil.
end;

Answer 5

if not Assigned(SomeForm) then begin
  Application.CreateForm(TSomeForm,SomeForm);
  try
    SomeForm.ShowModel;
  finally
    SomeForm.Free;
    SomeForm:=nil;
  end;
end
else
  SomeForm.ShowModal;
end;如果用SHOW在onDestroy事件中将实例赋值为nil;