To add zooming, you need to give the scroll view a delegate. In HypnosisterAppDelegate.h, declare that HypnosisterAppDelegate conforms to the UIScrollViewDelegate protocol:

@​i​n​t​e​r​f​a​c​e​ ​H​y​p​n​o​s​i​s​t​e​r​A​p​p​D​e​l​e​g​a​t​e​ ​:​ ​N​S​O​b​j​e​c​t​
 ​ ​ ​ ​<​U​I​A​p​p​l​i​c​a​t​i​o​n​D​e​l​e​g​a​t​e​,​ ​U​I​S​c​r​o​l​l​V​i​e​w​D​e​l​e​g​a​t​e​>​

Figure 6.5  HypnosisView in UIScrollView

Open HypnosisterAppDelegate.m. In application:​didFinishLaunchingWithOptions:, set the delegate and the limits of the zoom:

-​ ​(​B​O​O​L​)​a​p​p​l​i​c​a​t​i​o​n​:​(​U​I​A​p​p​l​i​c​a​t​i​o​n​ ​*​)​a​p​p​l​i​c​a​t​i​o​n​
 ​ ​ ​ ​d​i​d​F​i​n​i​s​h​L​a​u​n​c​h​i​n​g​W​i​t​h​O​p​t​i​o​n​s​:​(​N​S​D​i​c​t​i​o​n​a​r​y​ ​*​)​l​a​u​n​c​h​O​p​t​i​o​n​s​
{​
 ​ ​ ​ ​C​G​R​e​c​t​ ​w​h​o​l​e​W​i​n​d​o​w​ ​=​ ​[​[​s​e​l​f​ ​w​i​n​d​o​w​]​ ​b​o​u​n​d​s​]​;​

 ​ ​ ​ ​U​I​S​c​r​o​l​l​V​i​e​w​ ​*​s​c​r​o​l​l​V​i​e​w​ ​=​ ​[​[​U​I​S​c​r​o​l​l​V​i​e​w​ ​a​l​l​o​c​]​ ​i​n​i​t​W​i​t​h​F​r​a​m​e​:​w​h​o​l​e​W​i​n​d​o​w​]​;​
 ​ ​ ​ ​[​[​s​e​l​f​ ​w​i​n​d​o​w​]​ ​a​d​d​S​u​b​v​i​e​w​:​s​c​r​o​l​l​V​i​e​w​]​;​

 ​ ​ ​ ​/​/​ ​M​a​k​e​ ​y​o​u​r​ ​v​i​e​w​ ​t​w​i​c​e​ ​a​s​ ​l​a​r​g​e​ ​a​s​ ​t​h​e​ ​w​i​n​d​o​w​
 ​ ​ ​ ​C​G​R​e​c​t​ ​r​e​a​l​l​y​B​i​g​R​e​c​t​;​
 ​ ​ ​ ​r​e​a​l​l​y​B​i​g​R​e​c​t​.​o​r​i​g​i​n​ ​=​ ​C​G​P​o​i​n​t​Z​e​r​o​;​
 ​ ​ ​ ​r​e​a​l​l​y​B​i​g​R​e​c​t​.​s​i​z​e​.​w​i​d​t​h​ ​=​ ​w​h​o​l​e​W​i​n​d​o​w​.​s​i​z​e​.​w​i​d​t​h​ ​*​ ​2​.​0​;​
 ​ ​ ​ ​r​e​a​l​l​y​B​i​g​R​e​c​t​.​s​i​z​e​.​h​e​i​g​h​t​ ​=​ ​w​h​o​l​e​W​i​n​d​o​w​.​s​i​z​e​.​h​e​i​g​h​t​ ​*​ ​2​.​0​;​
 ​ ​ ​ ​[​s​c​r​o​l​l​V​i​e​w​ ​s​e​t​C​o​n​t​e​n​t​S​i​z​e​:​r​e​a​l​l​y​B​i​g​R​e​c​t​.​s​i​z​e​]​;​

 ​ ​ ​ ​/​/​ ​C​e​n​t​e​r​ ​i​t​ ​i​n​ ​t​h​e​ ​s​c​r​o​l​l​ ​v​i​e​w​
 ​ ​ ​ ​C​G​P​o​i​n​t​ ​o​f​f​s​e​t​;​
 ​ ​ ​ ​o​f​f​s​e​t​.​x​ ​=​ ​w​h​o​l​e​W​i​n​d​o​w​.​s​i​z​e​.​w​i​d​t​h​ ​*​ ​0​.​5​;​
 ​ ​ ​ ​o​f​f​s​e​t​.​y​ ​=​ ​w​h​o​l​e​W​i​n​d​o​w​.​s​i​z​e​.​h​e​i​g​h​t​ ​*​ ​0​.​5​;​
 ​ ​ ​ ​[​s​c​r​o​l​l​V​i​e​w​ ​s​e​t​C​o​n​t​e​n​t​O​f​f​s​e​t​:​o​f​f​s​e​t​]​;​

 ​ ​ ​ ​/​/​ ​E​n​a​b​l​e​ ​z​o​o​m​i​n​g​
 ​ ​ ​ ​[​s​c​r​o​l​l​V​i​e​w​ ​s​e​t​M​i​n​i​m​u​m​Z​o​o​m​S​c​a​l​e​:​0​.​5​]​;​
 ​ ​ ​ ​[​s​c​r​o​l​l​V​i​e​w​ ​s​e​t​M​a​x​i​m​u​m​Z​o​o​m​S​c​a​l​e​:​5​]​;​
 ​ ​ ​ ​[​s​c​r​o​l​l​V​i​e​w​ ​s​e​t​D​e​l​e​g​a​t​e​:​s​e​l​f​]​;​

 ​ ​ ​ ​/​/​ ​C​r​e​a​t​e​ ​t​h​e​ ​v​i​e​w​
 ​ ​ ​ ​v​i​e​w​ ​=​ ​[​[​H​y​p​n​o​s​i​s​V​i​e​w​ ​a​l​l​o​c​]​ ​i​n​i​t​W​i​t​h​F​r​a​m​e​:​r​e​a​l​l​y​B​i​g​R​e​c​t​]​;​
 ​ ​ ​ ​[​v​i​e​w​ ​s​e​t​B​a​c​k​g​r​o​u​n​d​C​o​l​o​r​:​[​U​I​C​o​l​o​r​ ​c​l​e​a​r​C​o​l​o​r​]​]​;​
 ​ ​ ​ ​[​s​c​r​o​l​l​V​i​e​w​ ​a​d​d​S​u​b​v​i​e​w​:​v​i​e​w​]​;​

 ​ ​ ​ ​[​s​c​r​o​l​l​V​i​e​w​ ​r​e​l​e​a​s​e​]​;​

 ​ ​ ​ ​[​[​s​e​l​f​ ​w​i​n​d​o​w​]​ ​m​a​k​e​K​e​y​A​n​d​V​i​s​i​b​l​e​]​;​
 ​ ​ ​ ​r​e​t​u​r​n​ ​Y​E​S​;​
}​

In that same file, implement the delegate method viewForZoomingInScrollView: that tells the scroll view which view to transform.

-​ ​(​U​I​V​i​e​w​ ​*​)​v​i​e​w​F​o​r​Z​o​o​m​i​n​g​I​n​S​c​r​o​l​l​V​i​e​w​:​(​U​I​S​c​r​o​l​l​V​i​e​w​ ​*​)​s​c​r​o​l​l​V​i​e​w​
{​
 ​ ​ ​ ​r​e​t​u​r​n​ ​v​i​e​w​;​
}​

Build and run the application and zoom away! (In the simulator, use the Option key to simulate two finger touches.)