Maxim Pavlov imaks

libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.
Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

Videos

Introduction to Functional Programming Johannes Weiß - https://vimeo.com/100786088
ReactiveCocoa at MobiDevDay Andrew Sardone - https://vimeo.com/65637501
The Future Of ReactiveCocoa Justin Spahr-Summers - https://www.youtube.com/watch?v=ICNjRS2X8WM
Enemy of the State Justin Spahr-Summers - https://www.youtube.com/watch?v=7AqXBuJOJkY
WWDC 2014 Session 229 - Advanced iOS Application Architecture and Patterns Andy Matuschak - https://developer.apple.com/videos/play/wwdc2014/229/
Functioning as a Functionalist Andy Matuschak - https://www.youtube.com/watch?v=rJosPrqBqrA
Controlling Complexity in Swift Andy Matuschak - https://realm.io/news/andy-matuschak-controlling-complexity/

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.

If you've haven't seen it before, there is a cool accessibility feature in UITableView that allows the user to toggle between different actions. It's really very elegant and it's a powerful and convenient implementation for VoiceOver users on iOS. One could say that it's the VoiceOver version of the swipe-to-delete feature.

To try it out yourselves, open one of the built in apps like Mail or Notes and turn on VoiceOver. If you are afraid to accidentally delete some of your important notes or email, you can also create a new Master-Detail Application in Xcode and run it on your device. Navigate to one of the cells and use the "Rotor" (rotate with two fingers on the screen) to find the "Actions" item. Now you can swipe up and down do toggle between "Activate Item (default action)" and "Delete". If you now double tap, the cell gets deleted instead of selected.

This is the default behavior and you get this accessibility out of the box with UITableView.

	# The trick is to link the DeviceSupport folder from the beta to the stable version.
	# sudo needed if you run the Mac App Store version. Always download the dmg instead... you'll thank me later :)

	# Support iOS 15 devices (Xcode 13.0) with Xcode 12.5:
	sudo ln -s /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/15.0 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport

	# Then restart Xcode and reconnect your devices. You will need to do that for every beta of future iOS versions

	# (A similar approach works for older versions too, just change the version number after DeviceSupport)

	//
	// RecordAudio.swift
	//
	// This is a Swift class (updated for Swift 5)
	// that uses the iOS RemoteIO Audio Unit
	// to record audio input samples,
	// (should be instantiated as a singleton object.)
	//
	// Created by Ronald Nicholson on 10/21/16.
	// Copyright © 2017,2019 HotPaw Productions. All rights reserved.

	/// 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

	//
	// Warnings.xcconfig
	//
	// The list of warnings we (don’t) use, and the reasons why.
	//
	// :MARK: Warnings in use:
	// :MARK: -everything
	// We want the best possible diagnostics, so we simply enable everything that exists, and then opt–out of what doesn’t make sense for us.
	//
	// :MARK: - Warnings not to be promoted:

	//
	// Defaults.xcconfig
	//
	// Common customizations/sanitizations of the platform defaults for our projects.
	//
	// For compatibility reasons, the iOS platform has a couple of not–so–sensible defaults.
	// This file collects, and annotates the deviations from these defaults.
	//
	// :NOTE: Some of the settings herein may be redundant for newly created projects/targets:
	// Xcode’s project/target templates take several (but not all!) of these issues into account.