I want to save DB when the back button clicked in navigation controller.
so I would insert code in method.
What method is called when back button clicked in navigation controller?
To do what you asked, look at the UINavigationControllerDelegate
protocol, namely the method:
- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated
when the viewController argument is no longer your view controller then you should save.
However, doing so on viewWillDisappear:
might be a better (and much simpler) idea.