struct MyDlg : public WithMydialogLayout<TopWindow> {
	...
	void DoAction();
	...
	MyDlg() {
		...
		action.WhenPush <<= THISBACK(DoAction);
	}
}

MyDlg::DoAction() {
...
}

error : 'DoAction' is not a member of 'Upp:TopWindow'

WithMydialogLayout<TopWindow>

typedef MyDlg CLASSNAME;

error: no match for ‘operator<<=’ in ‘((MyDlg*)this)->MyDlg::<anonymous>.WithMydialogLayout<Upp::TopWindow>::DoAction.Upp::Button::<anonymous>.Upp::Pusher::WhenPush <<= Upp::callback(OBJECT*, void (METHOD::*)()) [with OBJECT = MyDlg, METHOD = MyDlg](&MyDlg::DoAction)’

MyDlg() {
		...
		action.WhenPush = THISBACK(DoAction);
	}

MyDlg() {
		...
		action <<= THISBACK(DoAction); // Sets WhenAction
	/*OR*/	action.WhenAction = THISBACK(DoAction);
	/*OR*/	action.WhenPush = THISBACK(DoAction); // If you really want WhenPush
	}