How to create a Tinder type UINavigationController?

I have went through some tutorials and example projects to find out a way to create a UINavigationController like in the Tinder app. This is the best example that I've got so far : http://ift.tt/1BntgBy

But the problem I'm facing is, I have no idea to animate the buttons like in the Tinder app. Please check this image:

Does anyone know how to achieve this?