The interface is notifying the receiver that the user is scrolling to the bottom of UIScrollview.

If you have a toolbar at the bottom and hiding it, the delegate will give you a chance to show the toolbar.

The code to use the interface should like this: 
`
    [self moveNavigtionBar:deltaY animated:YES];
    [self moveToolbar:-deltaY animated:YES]; // move to revese direction
    [self updateToolbarItems]; // Workaround iOS 7's bug: sometime the toolbar items will not be displayed
`