What’s up with App Icons?

When you create an image set in Xcode, it’s so easy to automatically fill the wells for each scale factor. You just need to give each the three scale factor image files the correct syntax, something like:

  • image.png
  • image_2x.png
  • image_3x.png

Drag them in and Xcode automatically detects the correct well for each image, and tada!


So you’d think it would be just as easy to set up an app icon in the asset catalog. There is some automation there, but weirdly it’s a bit hit and miss.


Let’s look at what we can do about this.

Generating App Icon files

First, how to set up all of these versions of the app icon?

Easy! Apple provides a Photoshop (or Sketch or Adobe XD) template in the resources section of HIG for setting up an icon, that looks something like:

Screenshot 2018-08-01 13.20.52.png

Once you’ve set up your icon, you can specify File > Generate > Image Assets:

Screenshot 2018-08-01 13.21.05.png

And this will output all the files you’ll need to create an app icon:

Screenshot 2018-08-01 13.22.34.png

Adding icons to Asset Catalog

However, as we saw, when you drag these icons into your app icon:

Screenshot 2018-08-01 13.23.34.png

Only some wells fill, others stay blank, and some files are treated as unassigned:


Your first question might be:


My guess is this is a bug in Xcode, if anyone has more info on this feel free to add a comment here. But maybe a more pertinent question is…

What to do about this?

Fix it manually

So – of course one solution is to resolve this manually, by dragging files one by one into their correct wells. Boring! We want automation!

Fix the automation

So, if you right-click on the app icon in the asset catalog, and select ‘Show in Finder’:

Screenshot 2018-08-01 21.40.43.png

Here you’ll find all of the icon files inside the project, along with a ‘Contents.json’ file:

Screenshot 2018-08-01 21.40.18.png

Here’s the magic! The Contents.json is a file used by the asset catalog to describe its assets (or folders, metadata, etc.) If you open the Contents.json file for the AppIcon you’ll find that it describes all of the app icon files, blank wells and unassigned images, something like this:

Screenshot 2018-08-01 23.13.00.png

So all the files we need are in the AppIcon folder in the Assets Catalog, we just need them to be assigned correctly in the Contents.json file. If we’ve used the Photoshop template, our files will have the same names every time, so we can simply replace the Contents.json with a standard Contents.json file that has been set up with the correct description of the files, and everything should automatically drop into the correct wells!

So, as a recap, here are the steps to follow after generating your icon files from Photoshop:

  1. Select all of the files you’ve generated (except for Icon-App-60×60@1x.png, this file is no longer included in the app icon package) and drag them as per usual into the App Icon in the Assets Catalog in Xcode.
  2. Right-click on the App Icon, and select Show in Finder. Here you’ll find the Contents.json file.
  3. Replace this Contents.json file with a corrected Contents.json file. (You can find a gist for this file here.)
  4. Tada!


There’s an app for that!

Of course there are also lots of third party solutions. Be careful though, there are plenty (even paid Mac programs) that merely create the files for you (exactly what the Photoshop template does for you) without helping you to integrate these files into Xcode.

Icon Set Creator (link here) is free and not only generates the files for you, but also generates the Contents.json file. This means you can simply import this folder into the Asset Catalog and the files will slot into their wells.


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Posted in Swift

What’s new Swift 4.2?

The latest update of Swift 4.2 came out last week at WWDC, and it has some pretty exciting improvements.

Some had me thinking ‘that’ll be useful’, some had me excited and some, to be honest, had me thinking ‘FINALLY!’ Here are some of my highlights:



One feature that I’m especially pleased about is random. Random has always been a sticking point for me in Swift – arc4random, arc4random_uniform, and drand48  have seemed out of place – more like an artifact from ancient history than a part of a ‘modern’ language, and in fact, they were! These methods directly accessed lower level C APIs.

arc4random and arc4random_uniform used and returned the little used UInt32 type (Int and UInt are much more common in Swift, which automatically uses either the 32 or 64 bit version depending on the platform your app is running on.) This means that the parameter being passed and the response always had to be converted, making a request for random extra verbose. Want a random integer between 0 and 10? Take a look at this:

let max = 10
//pre Swift 4.2
let result = Int(arc4random_uniform(UInt32(max)))

Wow. See what I mean? And if the laborious syntax isn’t a convincing enough reason – arc4random didn’t return uniform distribution of random numbers, drand48 (though it did return more useful data type Double) required an additional step of seeding, and let’s be honest – these methods had horribly ugly names!

Well – breathe a sigh of relief because Swift 4.2 has a new and exciting API with a whole range of convenience methods to make our lives easier as developers.

Remember the random integer between 0 and 10? How about this:

let max = 10
//Swift 4.2
let result = Int.random (in: 0 ..< max)

Much simpler and more readable, right? And it doesn’t have to be an integer, all numeric types have a random method now – here’s the Double version:

let max = 10
//Swift 4.2
let result = Double.random (in: 0 ..< max)

There are even collection convenience methods that select a random element.
Want to pick a suit, any suit? Too easy now:

var suits = ["Hearts","Diamonds","Clubs","Spades"]
//Swift 4.2
let suit = suits.randomElement()!

Want to shuffle the suits? Just as easy:

//Swift 4.2

You can check out the Swift Evolution proposal for random unification here.

Bool toggle

Speaking of neat little convenience methods, here’s another!

You can now simply call the toggle method on a boolean.

No more:

//pre Swift 4.2
soundOn = !soundOn

You can now do this:

//Swift 4.2

You can check out the Swift Evolution proposal for adding toggle to Bool here.

New Collection higher order functions

When higher order functions come up, people often discuss the big four – map, filter, reduce and sort. In my post on higher order functions in Swift, I looked at a whole bunch of other higher order functions that collection types offer. Well, in Swift 4.2 we have more!


Whereas the contains method returns a Bool based on whether at least one element in a collection satisfies a condition, the new allSatisfy method returns a Bool based on whether all elements satisfy a condition. For example:

var fruits = ["Banana","Banana","Coconut","Banana","Banana","Banana"]
//Swift 4.2
let completelyBananas = fruits.allSatisfy { $0 == "Banana" } //false

Check out the SE proposal here.

First and last

We previously had methods index(of:) and index(where:) which found the first item which satisfied a condition. We now have lastIndex(of:) and lastIndex(where:) too, which finds the last item in the collection that satisfies a condition. It made sense then to change the name of the index methods to firstIndex(of:) and firstIndex(where:).

You can find the SE proposal for first and last methods here.

Remove all

Remember the confusion you had when you first tried to remove all items from an array that satisfied a condition using a simple for loop?
You may have programmed something like:

var fruits = ["Banana","Banana","Coconut","Banana","Banana"]
//remove all bananas (naive implementation)
for (index,fruit) in fruits.enumerated() {
  if fruit == "Banana" {
    fruits.remove(at: index)

Then everything really did go bananas when an Index out of Range error appeared in the console?


Ah for more innocent days.

Of course the index had continued to increment while the number of elements in the array steadily decreased, until finally the loop index was higher than the number of elements in the array, causing a crash. There were solutions to this problem of course – loop in reverse, for example, or use the filter method, but now we have a method built for just this task, removeAll. Take a look:

var fruits = ["Banana","Banana","Coconut","Banana","Banana"]
//remove all bananas (Swift 4.2)
fruits.removeAll { $0 == "Banana" }

Well,​ that was easier! You can find the SE proposal for remove all collection method here.

Looping through enumerations

I remember years ago having an enumeration nicely set up – I think it was something like an enum for card suits…

enum Suit {
  case hearts
  case diamonds
  case clubs
  case spades

…and I remember realizing I needed to loop through the cards. (Perhaps it was to find a random suit) I remember thinking – well that shouldn’t be so hard, I already have the enum set up, right?

I then realized that this isn’t a default feature of enums, and I remember thinking, “whaaa?”


Of course,​ there was a way around this – you could set up a static variable for example that contained an array of all the items in the enum:

//pre Swift 4.2
enum Suit {
  case hearts
  case diamonds
  case clubs
  case spades
  static var allCases:[Suit] = [.hearts, .diamonds, .clubs, .spades]

You could then use this allCases property to loop through the cases:

for suit in Suit.allCases {

Well, Swift 4.2 (FINALLY!) can automatically synthesize this for you. All you need to do is adopt the CaseIterable protocol.

//Swift 4.2
enum Suit:CaseIterable {
  case hearts
  case diamonds
  case clubs
  case spades

Imagine – combined with the new collection convenience methods, we could now shuffle your enum case suits:

//Swift 4.2
var suitsShuffled = Suit.allCases.shuffled()

Or pick a random suit!

//Swift 4.2
var pickASuitAnySuit = Suit.allCases.randomElement()!

Wow! You can find the SE proposal for the all cases property for enums here.

Well – that’s plenty to be excited about with Swift 4.2, and I haven’t even covered everything new! If you’re interested in reading about other proposals I haven’t mentioned that made it into Swift 4.2 or perhaps are on their way for Swift 5, you can take a look over at the Swift Evolution page.

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Posted in Swift

Check out my livevideo course “iOS Development with Swift in Motion”!

I’d love for you to check out my video course “iOS Development with Swift in Motion”.


The course is out on Manning’s livevideo platform, and if you get in early with Manning’s early access program you can get 40% off with code ytgrummitt at manning.com.

See you in the videos!


Posted in Swift

Block comments, key bindings and feeling foolish!

Do you ever get stuck on something, and then when you work out what you were doing wrong you feel a bit foolish?

I was just thinking – it would be much more convenient if there was a keyboard shortcut to block comment some code. I know that with the keyboard shortcut Command-/ you can automatically generate single line comments:


But what I was after was a keyboard shortcut to generate block comments. Strangely this capability seems to be missing from Xcode, but I happened upon an Xcode Source Editor extension called BlockComment that seemed to do the job.

So – after installing BlockComment, I went into the Key Bindings tab in Xcode preferences, double clicked on the BlockComment binding to add a keyboard shortcut, and… nothing.BlockComment1.gif

I closed Xcode, opened Xcode – did it again and… nothing. I’ve done this before, how strange! Read up on key bindings, hmm… yes I seem to be doing the right thing, what could be going wrong?

Then I watched a video and that was when I felt foolish.

Of course! You can’t just click anywhere on the line – you need to click in the key field on the right!


Sometimes when you work out what you were doing wrong, it all seems so obvious!

So! Things I’ve learned today

FIRST – When customizing a keyboard shortcut in Key bindings – click in the Key field!

SECONDBlockComment – works quite well, I recommend!


THIRD – sometimes there’s no substitute for a video tutorial!

You might think that’s a strange sentiment for a book author, but as it turns out I’m currently working on a video course to accompany the book!

Of course, everyone has a preference for how to learn. Maybe you like books coz you can read them on the train. Maybe you prefer videos as you find it easier to learn visually. Either way, you have a choice now when learning iOS development with Swift.


You can check out the book “iOS Development with Swift” here.

Or – you can check out the livevideo course “iOS Development with Swift in Motion” here. The video course is currently in the Manning early access program, and new Units will be put out regularly.

You can use both together or independently, depending on your preference!

Good luck with them, and enjoy block commenting your code with keyboard shortcuts!

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Posted in Swift

Learn iOS and Swift – interactive video course

Exciting news! For most of this year I’ve been busy working on a series of video tutorials in iOS and Swift, and this week we’re launching the Manning Early Access Program(MEAP) for the course.

There will be 13 units in total – with approximately half an hour per unit that should be hours and hours of quality content to get you up and going in iOS and Swift.

You can check out the home for the video tutorials at Manning here, or watch a preview of the course here. To promote the launch, I have a special secret discount code ( vlgrummitt ) you can use to get 50% off, but you’ll need to move fast – it’s only valid until May 3.

You can use the video tutorials exclusively if you like, or even better – as an accompaniment to my book iOS Development with Swift, out now.

So if you’ve been thinking about learning iOS or Swift – now’s the time to dive in!



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Learn iOS Development with Swift now!

Exciting news – the book I have been working on for almost two years, iOS Development with Swift, is now done, published, printed and available on Amazon or in a bookstore near you.

The book is aimed at experienced programmers looking to migrate into developing in iOS with Swift. It assumes no previous knowledge of Swift nor iOS but skips over all the stuff you’ll already know from your experience in other languages.

After getting you up to speed on what’s new and exciting in Swift, the book takes you through building up an app from zero to App Store, exploring many different challenges you may encounter when working on an app, such as:

  • How do you deal with different devices or orientations?
  • What do you do if the keyboard pops up and covers the text field the user is editing?
  • What are different ways of navigating between scenes?
  • How do scenes communicate with each other?
  • How can you integrate animation and adaptive layout?
  • How can you handle background tasks?
  • What are the different ways of storing data locally and in iCloud?
  • What options are available for debugging in Xcode?

I’m very much looking forward to seeing the apps that readers produce after exploring iOS development with the support of the book! Do let me know about your app creations via Twitter, and I’ll post them on the website for the book.

If you’re interested in taking a peek at iOS Development with Swift, you can check it out now as a live book using Manning’s online reader.

Posted in Swift

Migrating from AS3 to Swift

As iOS 11 no longer supports 32 bit apps, I’ve been revisiting an old app that was built in Flash/ActionScript3 (and packed in 32 bit) and decided it was an opportune moment to migrate it to native iOS Xcode/Swift. Migration was quite an interesting experience, and ultimately gave me a new appreciation for Xcode/Swift, especially auto-layout, size classes, enums and type-strictness.

In general, the app looks and acts virtually identically to its predecessor. Here is the main menu for you:


But in some cases, a change was necessary. As Flash did not have access to native controls, a custom solution was used using a Starling framework called Feathers. Of course from Xcode/Swift native controls were available. I used form builder Eureka to build this up. Here’s the difference:


Charts looked a little differently too. Charts in Flash used a long-dead yahoo framework called Astra. Charts now use Daniel Gindi’s huge Charts framework, which adds some pretty cool features such as pinch to zoom and drag. Here’s the difference:


One problem that I wasn’t able to resolve was detecting data from the old version of the app in new version of the app. I couldn’t find technical information on how Air’s SharedObject was implemented, so unfortunately data has to be reset from this version. Still, better than the app simply not working!

If you’re interested in checking out the new version of the app, you can find it here.




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Posted in AIR, Flash, Swift