IPhone : Height constraint to iOS 8 custom keyboard not working

I tried using the following code to change the height of the keyboard (From https://developer.apple.com/library/prerelease/ios/documentation/General/Conceptual/ExtensibilityPG/Keyboard.html)

CGFloat _expandedHeight = 500;
NSLayoutConstraint *_heightConstraint = [NSLayoutConstraint constraintWithItem: self.keyboard attribute: NSLayoutAttributeHeight relatedBy: NSLayoutRelationEqual toItem: nil attribute: NSLayoutAttributeNotAnAttribute multiplier: 0.0 constant: _expandedHeight];
[self.keyboard addConstraint: _heightConstraint];

But it is not changing the height. (self.keyboard comes from @property (strong,nonatomic) Keyboard *keyboard;). I have also have a view inside the keyboard (self.keyboard.view1).

View1 also has constraints put in storyboard (Trailing Space to: Superview, Leading Space to: Superview, Bottom Space to: Superview, and Top Space to: Superview).