Improvised KVO

ObservationHelper.swift

/*

ObservationHelper.swift is published under the MIT License.

Copyright (C) 2014-15, Roopesh Chander http://roopc.net/

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

// Usage:
// var observer1 = object.onChange("property") { change in
//                    doSomethingWithChangeDict(change)
//                }
// var observer2 = object.onNotification(NSMetadataQueryDidFinishGatheringNotification) {
//                    notification in
//                    doSomethingWithNotificationDict(notification.userInfo)
//                }
// // Keep a strong reference to the returned observer objects
// // as long as you want to observe said thingie.

import Foundation

extension NSObject {
    func onChange(keyPath: String, options: NSKeyValueObservingOptions,
        runBlock block: (change: [NSObject : AnyObject]!) -> ()) -> AnyObject {

        return KeyValueObserver(object: self, keyPath: keyPath, options: options, block: block)
            as AnyObject

    }

    func onChange(keyPath: String,
        runBlock block: (change: [NSObject : AnyObject]!) -> ()) -> AnyObject {

        return KeyValueObserver(object: self, keyPath: keyPath, options: nil, block: block)
            as AnyObject

    }

    func onChangeInAnyOf(keyPaths: [String], options: NSKeyValueObservingOptions,
        runBlock block: (keyPath: String, change: [NSObject : AnyObject]!) -> ()) -> AnyObject {

            return KeyValueObserverMultiKey(object: self, keyPaths: keyPaths, options: options, block: block)
                as AnyObject

    }

    func onChangeInAnyOf(keyPaths: [String],
        runBlock block: (keyPath: String, change: [NSObject : AnyObject]!) -> ()) -> AnyObject {

            return KeyValueObserverMultiKey(object: self, keyPaths: keyPaths, options: nil, block: block)
                as AnyObject

    }

    func onNotification(name: String, runBlock block: ((NSNotification!) -> ())) -> AnyObject {

        return NotificationObserver(object: self, name: name, queue: NSOperationQueue.currentQueue(), block: block)
            as AnyObject

    }
}

func onGenericNotification(name: String, runBlock block: ((NSNotification!) -> ())) -> AnyObject {
    return NotificationObserver(object: nil, name: name, queue: NSOperationQueue.currentQueue(), block: block)
        as AnyObject

}

private class KeyValueObserver: NSObject {
    weak var _object: NSObject?
    var _keyPath: String
    var _block: (change: [NSObject : AnyObject]!) -> ()

    init(object: NSObject, keyPath: String, options: NSKeyValueObservingOptions,
        block: (change: [NSObject : AnyObject]!) -> ()) {

        _object = object
        _keyPath = keyPath
        _block = block
        super.init()
        object.addObserver(self, forKeyPath: keyPath, options: options, context: nil)

    }

    override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject,
        change: [NSObject : AnyObject], context: UnsafeMutablePointer<()>) {

        assert(keyPath == _keyPath)
        _block(change: change)

    }

    deinit {
        _object?.removeObserver(self, forKeyPath: _keyPath, context: nil)
    }
}

private class KeyValueObserverMultiKey: NSObject {
    weak var _object: NSObject?
    var _keyPaths: [String]
    var _block: (keyPath: String, change: [NSObject : AnyObject]!) -> ()

    init(object: NSObject, keyPaths: [String], options: NSKeyValueObservingOptions,
        block: (keyPath: String, change: [NSObject : AnyObject]!) -> ()) {

            _object = object
            _keyPaths = keyPaths
            _block = block
            super.init()
            for keyPath in keyPaths {
                object.addObserver(self, forKeyPath: keyPath, options: options, context: nil)
            }

    }

    override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject,
        change: [NSObject : AnyObject], context: UnsafeMutablePointer<()>) {

            _block(keyPath: keyPath, change: change)

    }

    deinit {
        for keyPath in _keyPaths {
            _object?.removeObserver(self, forKeyPath: keyPath, context: nil)
        }
    }
}

private class NotificationObserver: NSObject {
    var _observerObject: AnyObject?

    init(object: NSObject?, name: String!, queue: NSOperationQueue!,
        block: ((NSNotification!) -> ())) {

        super.init()
        _observerObject = NSNotificationCenter.defaultCenter().addObserverForName(name, object: object,
            queue: queue, usingBlock: block)
    }

    deinit {
        if let observer: AnyObject = _observerObject {
            NSNotificationCenter.defaultCenter().removeObserver(observer)
        }
    }
}