Dani Lazarov vaderdan

Hacking UIView animation blocks for fun and profit

In this article, I'm going to explore a way that we can create views that implement custom Core Animation property animations in a natural way.

As we know, layers in iOS come in two flavours: Backing layers and hosted layers. The only difference between them is that the view acts as the layer delegate for its backing layer, but not for any hosted sublayers.

In order to implement the UIView transactional animation blocks, UIView disables all animations by default and then re-enables them individually as required. It does this using the actionForLayer:forKey: method.

Somewhat strangely, UIView doesn't enable animations for every property that CALayer does by default. A notable example is the layer.contents property, which is animatable by default for a hosted layer, but cannot be animated using a UIView animation block.

	import UIKit

	/// Space view intented to be used with auto layout.
	/// Similar to UIStackView, setting a background color is not supported.
	final class SpaceView: UIView {

	// MARK: - Properties

	private let contentSize: CGSize

	extension Array {
	func parallelMap<U>(transform: Element -> U) -> [U] {
	var result: [U?] = Array<U?>(count: count, repeatedValue: nil)
	dispatch_apply(count, dispatch_get_global_queue(0, 0)) {
	result[$0] = transform(self[$0])
	}
	return result.map { $0! }
	}
	}

	/// Observes a run loop to detect any stalling or blocking that occurs.
	///
	/// This class is thread-safe.
	@interface GHRunLoopWatchdog : NSObject

	/// Initializes the receiver to watch the specified run loop, using a default
	/// stalling threshold.
	- (id)initWithRunLoop:(CFRunLoopRef)runLoop;

	/// Initializes the receiver to detect when the specified run loop blocks for

	import Foundation

	class Box<T> {
	let unbox: T
	init(_ value: T) { self.unbox = value }
	}

	struct Notification<A> {
	let name: String
	}

	// This accompanies http://chris.eidhof.nl/posts/repmin-in-swift.html

	import UIKit

	// Unfortunately, we need Box

	public class Box<T> {
	public let unbox: T
	public init(_ value: T) { self.unbox = value }
	}

	import Foundation

	// A bunch of convenience things
	func const <A, B> (b: B) -> A -> B {
	return { _ in b }
	}
	func repeat <A> (n: Int) -> A -> [A] {
	return { a in
	return map(Array(1...n), const(a))
	}

	Copyright 2015 Chris Eidhof

	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 OTHE

	import Foundation

	// Executes an array of blocks in parallel, but only returns after they're all done.

	func parallel(blocks: [() -> ()]) {
	let group = dispatch_group_create()
	let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
	for block in blocks {
	dispatch_group_async(group, queue, block)
	}

	//
	// main.swift
	// Routes
	//
	// Created by Chris Eidhof on 17/08/14.
	// Copyright (c) 2014 Chris Eidhof. All rights reserved.
	//

	import Foundation