CGAffineTransformstruct.UIView.animate()- Core Animation.
A CGAffineTransform is a structure that represents a specific kind of transformation that can be applied to any UIView and its subclasses.
Apple provides many helper functions (scaling, rotating, moving) to make animations easier. Each of these functions return a CGAffineTransform that can be assigned into a UIViews transform property. Core Animation calculates all the intermediary steps of this process automatically.
By default, UIKit animations have a "ease in, ease out" curve which means that movement starts slow, then accelerates, then slows down near the end.
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When you're trying to rotate a view, you have to provide the value in radians.
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Core Animation will always take the shortest route for a rotation to work. Supposing you have a view with a 0º rotation and you decide to make a 90º rotation, it will happen counter-clockwise. On the other hand, if you apply a 270º rotation to a view with 0º rotation, it will happen clockwise.
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A consequence of the last rule is that if you try to rotate a view 360º, nothing will happen. The same applies to bigger rotations, like 540º (360º + 180º), Core Animation will only rotate the view 180º.
Core Animation also allows to animate a UIView property like: background color, transparency, etc. You can animate multiple things at once if you want something complicated to happen.