More complex animations between the states of a component, like a button, can be cumbersome to create in Swift. The code is usually spread around multiple animation blocks. This is an attempt to modularize the code, and make writing complex animations simpler. Note: It still needs some work to hide some of the complexity.

The states of a View are made up of the states of its Subviews. For example, think of the states of a button. One state can have a blue label, and a black outer border, while another state of the same button can have a red label and a white outer border. In a more mathematical notation that would translate to:

State_1 = Subcomp_1_state_1 + Subcomp_2_state_1 + ...

State_2 = Subcomp_1_state_2 + Subcomp_2_state_2 + ...

"+" denotes composition.

We need a way to encapsulate this information. What is there to encapsulate? First, the information about each Subview for a certain View state. And then the information about a View state.

I chose to encapsulate the information about a Subview in a 'Transition' struct:

struct Transition {
    let beforeTransition: (() -> ())?
    let afterTransition:  (() -> ())?
    let endState: () -> ()
    let animationDetails: AnimationDetails
}

The naming might be a bit confusing, I am sorry for that. The most important piece of info in a 'Transition' is the endState. The endState describes the look of that subcomponent for a certain View state. For example: If we have a View state, let's call it View_State_1, then the endState should contain the information about how that Subview is supposed to look like when the view is in View_State_1.

Once the Subview states are defined for a certain View state, then we can put them together to describe the state of the View. So we can form a collection of 'Transition' structs and call that the View state. Maybe a bit of notation will make it clearer:

Subview_State_1 = Transition1

Subview_State_2 = Transition2

View_State = [Transition1, Transition2]

Once we have 2 View states, say View_State_1 and View_State_2, we can animate the transition between View_State_1 and View_State_2.

Before the animation takes place, each View state needs to be converted into an Animator. This is an internal detail, which should be hidden in the future. But it is good to know about it if you want to understand how this works.

struct Animator {
    let beforeTransitions: [() -> ()]
    let propertyAnimator: UIViewPropertyAnimator
}

Animators are then passed to the StateAnimator, who starts the animation immediately.

For more information please consult the code.

Too much boilerplate is needed to do this.

Requires cocoapods. Run pod install

iOS 10

New York: http://wallpaperswide.com/new_york_city_buildings-wallpapers.html

Background: http://www.idownloadblog.com/2014/09/10/new-ios-8-wallpapers/

MIT License