Converting Swift convenience initializer to Objective-C - ios

Question

I need to convert the following convenience initializer from Swift to Objective-C
convenience init(view: UIView, overlapHandler: (CGRect)->()) {
self.init(view: view, handler: { overlap -> () in
overlapHandler(overlap ?? CGRect.nullRect)
})
}
My first attempt was:
-(instancetype) initWithView:(UIView*)view overlapHandler:(Handler)handler
{
Handler overlapHandler = ^(CGRect overlap) {
if (CGRectIsNull(overlap)) {
return;
}
handler(overlap);
};
return [self initWithView:view andHandler:overlapHandler];
}
But it didn't work well as I don't see how an Objective-C block can receive a non-optional CGRect.
The context of the code is below:
import UIKit
class KeyboardOverlapNotifier:NSObject {
typealias Handler = (CGRect?) -> ()
let view:UIView
let handler:Handler
init(view:UIView, handler:Handler) {
self.view = view
self.handler = handler
super.init()
beginListening()
}
deinit {
stopListening()
}
func beginListening() {
token = token ?? nc.addObserverForName(UIKeyboardWillChangeFrameNotification,
object:nil, queue:nil, usingBlock:keyboardFrameDidChange)
}
func stopListening() {
if let observer = token {
nc.removeObserver(observer)
token = nil
}
}
private let nc:NSNotificationCenter = NSNotificationCenter.defaultCenter()
private var token:NSObjectProtocol?
}
private extension KeyboardOverlapNotifier {
func keyboardFrameDidChange(notification: NSNotification!) {
let duration = notification.userInfo!
[UIKeyboardAnimationDurationUserInfoKey] as NSTimeInterval
UIView.animateWithDuration(duration,
delay: 0,
options: .BeginFromCurrentState,
animations: {
let keyboard:CGRect = {
let global = (notification.userInfo!
[UIKeyboardFrameEndUserInfoKey] as NSValue).CGRectValue()
let local = self.view.convertRect(global, fromView: nil)
return local
}()
let overlap = self.view.bounds.rectByIntersecting(keyboard)
self.handler(overlap.nonEmptyOrNil)
},
completion: nil)
}
}
extension KeyboardOverlapNotifier {
convenience init(view: UIView, overlapHandler: (CGRect)->()) {
self.init(view: view, handler: { overlap -> () in
overlapHandler(overlap ?? CGRect.nullRect)
})
}
}
extension CGRect {
var nonEmptyOrNil:CGRect? { return !self.isEmpty ? self : nil }
}

Answer 1

Perhaps this should help? I'm still unsure what your question actually is so the only thing I can offer is references to each.
Closures are self-contained blocks of functionality that can be passed around and used in your code. Closures in Swift are similar to blocks in C and Objective-C and to lambdas in other programming languages.
Closures can capture and store references to any constants and variables from the context in which they are defined. This is known as closing over those constants and variables, hence the name “closures”. Swift handles all of the memory management of capturing for you.
Blocks vs Closures
https://www.codefellows.org/blog/writing-completion-blocks-with-closures-in-swift
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html