struct ChildAppWindow : TopWindow {
ChildAppWindow();
bool IsStop();
};

bool ChildAppWindow::IsStop()
{
// how can i cat bStop ( In class MyAppWindow)?
}

struct MyAppWindow : TopWindow {
MyAppWindow() ;

bool bStop;
void IsStop(bool& b) { b = bStop;}

ChildAppWindow child;

};

One way is like below:

Callback<bool&> cb_IsStop;
child.cb_IsStop = THISBACK(IsStop);

but this is not so convenient i think