Form Navigation Controller

FormNavigationController.swift

//
//  Copyright © 2014 Yuri Kotov
//

import UIKit

@objc
protocol FormNavigation {
    var nextField: UIResponder? {get}
}

class FormNavigationController: NSObject {
    let action: Selector = "textFieldDidReturn:"

    @IBOutlet
    var fields: [UITextField] = [] {
        willSet { unsubscribe(fields) }
        didSet { subscribe(fields) }
    }

    func subscribe(fields: [UITextField]) {
        fields.map { $0.addTarget(self, action: self.action, forControlEvents: UIControlEvents.EditingDidEndOnExit) }
    }

    func unsubscribe(fields: [UITextField]) {
        fields.map { $0.removeTarget(self, action: self.action, forControlEvents: UIControlEvents.EditingDidEndOnExit) }
    }

    func textFieldDidReturn(sender: UITextField) {
        if let field = sender as? FormNavigation {
            field.nextField?.becomeFirstResponder()
        } else if var index = find(fields, sender) {
            if ++index < fields.count {
                fields[index].becomeFirstResponder()
            }
        }
    }

    deinit {
        unsubscribe(fields)
    }
}