iOS Programming: The Big Nerd Ranch Guide

Bouncing with a CAKeyframeAnimation

For practice with CAKeyframeAnimation, you are going to make the time label grow and shrink to give it a bouncing effect (Figure 23.7).

Figure 23.7  Current time mid-bounce

Declare a new method in TimeViewController.h.

-​ ​(​v​o​i​d​)​b​o​u​n​c​e​T​i​m​e​L​a​b​e​l​;​

In TimeViewController.m, replace the code that spins the label in showCurrentTime: with a call to bounceTimeLabel.

-​ ​(​I​B​A​c​t​i​o​n​)​s​h​o​w​C​u​r​r​e​n​t​T​i​m​e​:​(​i​d​)​s​e​n​d​e​r​ {​ ​ ​ ​ ​N​S​D​a​t​e​ ​*​n​o​w​ ​=​ ​[​N​S​D​a​t​e​ ​d​a​t​e​]​;​ ​ ​ ​ ​s​t​a​t​i​c​ ​N​S​D​a​t​e​F​o​r​m​a​t​t​e​r​ ​*​f​o​r​m​a​t​t​e​r​ ​=​ ​n​i​l​;​ ...