CASpringAnimation

iOS9新出现的

/** Subclass for mass-spring animations. */

@interface CASpringAnimation : CABasicAnimation

/* The mass of the object attached to the end of the spring. Must be greater

than 0. Defaults to one. */

@property CGFloat mass;

/* The spring stiffness coefficient. Must be greater than 0.

* Defaults to 100. */

@property CGFloat stiffness;

/* The damping coefficient. Must be greater than or equal to 0.

* Defaults to 10. */

@property CGFloat damping;

/* The initial velocity of the object attached to the spring. Defaults

* to zero, which represents an unmoving object. Negative values

* represent the object moving away from the spring attachment point,

* positive values represent the object moving towards the spring

* attachment point. */

@property CGFloat initialVelocity;

/* Returns the estimated duration required for the spring system to be

* considered at rest. The duration is evaluated for the current animation

* parameters. */

@property(readonly) CFTimeInterval settlingDuration;

@end