Refactoring CNContactPicker UI Code using the delegate pattern in Swift - ios

Question

I have implemented the CNContactPickerViewController ContactsUI provided by iOS in iOS10 succesfully in a view controller so I can have a user select multiple contacts to invite to an event. I am trying to reduce the size of this single view controller by implementing the delegate pattern, and am stuck on a black screen. I have looked at a few resources, and think I am calling the delegate and defining the protocol accordingly. I have a view controller, CreateEventViewController and it implements my self defined ContactsToInviteDelegate. This protocol is as follows:
protocol ContactsToInviteDelegate : class {
//array of array of KV-pairs where inner array is {"email":"email#gmail.com", "phone": "[phone]"}
//array of JSON objects to upload
func contactsToInvite(_ contactsStructure: [[String:String]])
}
My ContactPickerViewController self defined class is as follows:
class ContactPickerViewController: UIViewController, CNContactPickerDelegate {
//class variables
let phoneNumberKit = PhoneNumberKit()
weak var delegate: ContactsToInviteDelegate?
var contactsToSendInvitesTo = [[String:String]]()
func contactPicker(_ picker: CNContactPickerViewController, didSelect contacts: [CNContact]) {
contacts.forEach { contact in
let phoneNum = contact.phoneNumbers.first
var stringPhoneNumber = String()
do{
let phoneNumber = try self.phoneNumberKit.parse((phoneNum?.value.stringValue)!, withRegion: "US", ignoreType:true)
stringPhoneNumber = "+1\(phoneNumber.adjustedNationalNumber())"
print(stringPhoneNumber)
}
catch {
print("phone number parsing error")
}
let contactDisplayName = contact.givenName
print("displayName: \(contactDisplayName)" )
let contactEmail = contact.emailAddresses.first?.value ?? ""
print("email: \(contactEmail)")
self.contactsToSendInvitesTo.append(["email":contactEmail as String, "phone":stringPhoneNumber])
}
delegate?.contactsToUpload(self.contactsToSendInvitesTo)
}
func contactPickerDidCancel(_ picker: CNContactPickerViewController) {
print("cancel contact picker")
}
func contactPicker(_ picker: CNContactPickerViewController,didSelectContactProperties contactProperties: [CNContactProperty]) {
}
}
And in the CreateEventViewController I am calling the delegate when i click the invite users button and implementing the method of the protocol to just attempt to print the final structure displaying contacts emails and phone numbers to send invitations to:
func selectContactsPicker() {
let cnPicker = ContactPickerViewController()
cnPicker.delegate = ContactPickerViewController() as? ContactsToInviteDelegate
self.present(cnPicker, animated:true, completion:nil)
}
func contactsToInvite(_ contactsStructure: [[String : String]]) {
print(contactsStructure)
}
This code without refactoring to try to use the delegate pattern worked before. I had all these functions within one single view controller, but with all the logic required this file itself is extending beyond 400+ lines. My problem now is that after attempting to refactor using the delegate pattern, when i click the button to trigger selectContactsPicker all I see is a black screen. I don't know what I am doing wrong, but I have a feeling it is this function itself. I am not quite sure what the body of this function should be in order to delegate the responsibility to the correct controller, or how to display it properly. Examples I saw used storyboards and segues, such as this. I looked at other examples for using delegates but I think my problem is a bit too specific and I don't know how to ask in a more general sense. If I did, I would probably not have this problem to begin with, as then I would probably properly understand how to implement the delegate pattern.

Answer 1

A delegate does not have to be a view controller. This is a convenient pattern when a view controller manages elements requiring delegates - rather than instantiate separate objects just let the view controller implement the protocol.
There are a number of ways to manage unruly view controllers which grow too large.
One simple way is to use extensions. To add a delegate protocol to an existing view controller:
extension SomeViewController : CNContactPickerDelegate {
... implement contact picker delegate methods
}
This can nicely compartmentalise your source code making it easier to read.
If you want to use a separate class instance as the delegate, that can be done quite easily too.
Declare your delegate class, either in the same source file or another:
class MyPickerDelegate : NSObject, CNContactPickerDelegate {
... implement contact picker delegate methods
}
note the class must inherit from NSObject, but does not need to be a UIViewController.
In the code where you fire up the contact picker:
picker = CNContactPickerViewController()
self.pickerDelegate = MyPickerDelegate()
picker.delegate = self.pickerDelegate
self.present(picker, animated: true)
Note picker view controller only keeps a weak reference to the delegate, so you must make sure to keep a strong reference to the object somewhere. Here I am using a property pickerDelegate