Address Book External Change Callback in Swift (with C Function Pointers?) - swift

Question

Original Question (see solution below):
I am trying to use the AddressBook.framework in my Swift App, but can't figure out how to implement the ABAddressBookRegisterExternalChangeCallback function.
In Objective-C, I just implement the callback as a C function and pass its pointer:
// somewhere in the initializer of the MyAddressBook class:
ABAddressBookRef addressBook = ABAddressBookCreateWithOptions(nil, nil);
ABAddressBookRegisterExternalChangeCallback(addressBook, externalChangeCallback, (__bridge void *)(self));
// somewhere else in the MyAddressBook class:
void externalChangeCallback(ABAddressBookRef reference, CFDictionaryRef info, void *context)
{
[(__bridge MyAddressBook *)context addressBookDidChangeExternally];
}
- (void)addressBookDidChangeExternally
{
// good old Obj-C from here on!
}
In Swift, it is proving very difficult for me to handle C functions. I found that Apple added the ability to pass C function pointers around in beta 3, but how do I declare such a function? It would be good to use Swift's closure syntax, but is that even possible here?
This is where I create the ABAddressBookRef:
var addressBookRef: ABAddressBookRef = {
let addressBookRef: ABAddressBookRef = ABAddressBookCreateWithOptions(nil, nil).takeRetainedValue()
// TODO: how do I make this work?
let externalChangeCallback: ABExternalChangeCallback = {
println("Address book changed externally!")
}
ABAddressBookRegisterExternalChangeCallback(addressBookRef, externalChangeCallback, nil)
return addressBookRef
}()
So how can I implement this in Swift?
Solution (with flaws):
As suggested by pNre, this is how I implemented it now:
In Objective-C:
AddressBookExternalChangeCallback.h:
#import <AddressBook/AddressBook.h>
void registerExternalChangeCallbackForAddressBook(ABAddressBookRef addressBookRef);
AddressBookExternalChangeCallback.m:
#import "AddressBookExternalChangeCallback.h"
void addressBookExternalChangeCallback(ABAddressBookRef addressBookRef, CFDictionaryRef info, void *context)
{
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:#"AddressBookDidChangeExternallyNotification" object:nil];
});
}
void registerExternalChangeCallbackForAddressBook(ABAddressBookRef addressBookRef)
{
ABAddressBookRegisterExternalChangeCallback(addressBookRef, addressBookExternalChangeCallback, nil);
}
In Swift:
after importing bridging header:
registerExternalChangeCallbackForAddressBook(addressBookRef)
A notification is posted whenever the address book changes. Only #objc classes can register for notifications, though, so is there a way to call a Swift function or method instead?

Answer 1

ABExternalChangeCallback is defined as
typealias ABExternalChangeCallback = CFunctionPointer<((ABAddressBookRef!, CFDictionary!, UnsafeMutablePointer<()>) -> Void)>
From the Xcode release notes:
However, you cannot call a C function pointer (CFunctionPointer) or
convert a closure to C function pointer type.
This means you can't assign a block the way you're doing.
However you can bypass this limitation calling ABAddressBookRegisterExternalChangeCallback in an objc function and calling it from your swift code.

Answer 2

Swift 2.0
if let addressBook = ABAddressBookCreateWithOptions(nil, nil) {
let ref = addressBook.takeRetainedValue()
let callback: #convention(c) (addressBookRef: ABAddressBookRef!, info: CFDictionaryRef!, context: UnsafeMutablePointer<Void>) -> Void = {
(addressBookRef, info, context) in
// do the things you want
}
let addressBookChangeCallback = unsafeBitCast(callback, ABExternalChangeCallback.self)
ABAddressBookRegisterExternalChangeCallback(ref, addressBookChangeCallback, nil)
}

Answer 3

in swift 4.0
class ABAddressBookManager: NSObject {
static let shared = ABAddressBookManager()
private var addressBook: ABAddressBook?
override init() {
super.init()
let addressBookForObserving = ABAddressBookCreate().takeRetainedValue()
let context = Unmanaged.passUnretained(self).toOpaque()
DispatchQueue.main.async {
ABAddressBookRegisterExternalChangeCallback(addressBookForObserving, { (addressBook, info, context) in
guard let context = context else {
return
}
let manager = Unmanaged<ABAddressBookManager>.fromOpaque(context).takeUnretainedValue()
//call manager's method
}
}
self.addressBook = addressBookForObserving
}
}

Answer 4

I got the same issue. But I have cleared the cache by calling ABAddressBookRevert() in addressbook object.