iOS 8 programmatic contraints for PageViewController - objective-c

Question

I have a PageViewController which I am programmatically adding to the current view via the following:
// Create the page view controller.
self.pageViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"homePageViewController"];
self.pageViewController.dataSource = self;
self.pageViewController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);
// Instantiate the first view controller.
UIViewController *startingViewController = [self viewControllerAtIndex:0];
[self.pageViewController setViewControllers:#[startingViewController]
direction:UIPageViewControllerNavigationDirectionForward
animated:NO
completion:^(BOOL finished) {
// Completion code
}];
// Add the page view controller to this root view controller.
[self addChildViewController:self.pageViewController];
[self.view addSubview:self.pageViewController.view];
[self.pageViewController didMoveToParentViewController:self];
This is working well, however I need to add a constraint the this as I have an image view above and I want the top of the PageViewController to attach to the bottom of the ImageView. I have tried:
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.headerImage attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.pageViewController attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]];
and although the code builds fine, I get and error
Constraint items must each be an instance of UIView or subclass'
I've also tried:
NSDictionary *views = #{#"view": self.pageViewController.view,
#"top": self.headerImage };
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"[top][view]" options:0 metrics:nil views:views]];
And although this build and runs without error, the constraint is not observed.
Any help greatly appreciated. Thanks