gistfile1.m

- (void)goToPreviousPage:(id)sender {
    int currentPage = [[self.pager.viewControllers objectAtIndex:0] idx];
    
    // Don't do anything if we're already at the first page
    if (currentPage =< 0) {
        return;
    }

    // Instead get the view controller of the previous page
    SomePageViewController *newInitialViewController = (SomePageViewController *)[self viewControllerAtIndex:(currentPage - 1)];
    NSArray *initialViewControllers = [NSArray arrayWithObject:newInitialViewController];
    
    // Do the setViewControllers: again but this time use direction animation:
    [self.pager setViewControllers:initialViewControllers direction:UIPageViewControllerNavigationDirectionReverse animated:YES completion:nil];
}