Errata

I think there is one missing point in this tutorial. You provide @IBOutlet for imageView but you never tell readers to really connect this outlet to the extension's view controller's UIImageView.

When creating a parental lock for the pool cover (characteristic), I could not find a "Locked" type (in HomeKit Accessory Simulator 1.0.1) . Maybe "Target Lock State" would work.

/Users/stephenzhou/Downloads/iOS-8-Swift-Programming-Cookbook-master/chapter-concurrency/Performing Non-UI Related Tasks/Performing Non-UI Related Tasks/ViewController.swift:102:14: 'NSData?' does not have a member named 'length'

let imageData = NSURLConnection.sendSynchronousRequest(urlRequest,
returningResponse: nil, error: &downloadError)

if imageData.length > 0{

"Popovers are used to display temporary information on the screen. They can be used both on regular and on compact size devices such as iPads and iPhones."

Popovers can only be used on iPads. When running on iPhone, you will get the following exception:
NSInvalidArgumentException - UIPopovercontroller initWithContentViewController called when not running under UIuserInterfaceIdiomPad

Works fine under iPad - tested on iPhone 6

http://stackoverflow.com/questions/7687917/error-exception-nsinvalidargumentexceptionpad

http://stackoverflow.com/questions/26865306/nsinvalidargumentexception-reason-uipopovercontroller-initwithcontentview

When converting the unmanaged object (emails) to a managed object (allEmails), it should be tested first. Thus after:

let emails: ABMultiValueRef = ABRecordCopyValue(person,
kABPersonEmailProperty).takeRetainedValue() as ABMultiValueRef

test with:

if ABMultiValueGetCount(emails) > 0 { ... }

before using the returned value.

It says in you book: "The delegate of an instance of UIPickerView has to conform to the UIPickerViewDelegate protocol and must implement all the @required methods of that protocol."

But when you look at the class reference (e.g. by holding cmd and pressing on "UIPickerViewDelegate" in Xcode) there is no required function with the tag "@required".

Not an important issue but a mistake anyway.

func isFlashAvailableOnRearCamera() -> Bool{
return UIImagePickerController.isFlashAvailableForCameraDevice(.Front)
}

Should be (.Rear).

Same code has the same error.

The badge counter code is written like the following, but the badge doesn't update:

/* Badge settings */
notification.applicationIconBadgeNumber++

This is the correct code:

// Badge settings
notification.applicationIconBadgeNumber =
UIApplication.sharedApplication().applicationIconBadgeNumber + 1

There should be a call to populateDatabase() in this method in order to illustrate the actual functionality of the app. As is, there are no results as the People database isn't populated (and thus there will never be a record that meets the criteria).