Whenever we write code, we want our code to be well-designed. We want it to be flexible, elegant and safe. We want to make sure that Swift’s type system and the compiler catch as many of our mistakes as possible. It’s especially interesting how Swift’s type system can help us avoid obvious errors. For example, Swift won’t allow you to assign an Int to a String property like this: var anInt = 10 anInt = "Hello, World!" The Swift compiler would show you an error that explains that you can’t assign a String to an Int and you’d understand this....

When your app shows images from the network in a table view or collection view, you need to load the images asynchronously to make sure your list scrolls smoothly. More importantly, you’ll need to somehow connect the image that you’re loading to the correct cell in your list (instead of table view or collection view, I’m going to say list from now on). And if the cell goes out of view and is reused to display new data with a new image, you’ll want to cancel the in-progress image load to make sure new images are loaded immediately. And, to...

Lots of iOS developers eventually run into code that calls upon DispatchQueue.main. It's often clear that this is done to update the UI, but I've seen more than a handful of cases where developers use DispatchQueue.main as an attempt to get their code to work if the UI doesn't update as they expect, or if they run into crashes they don't understand. For that reason, I would like to dedicate this post to the question "When should I use DispatchQueue.main? And Why?". Understanding what the main dispatch queue does In iOS, we use dispatch queues to perform work in parallel....

If you're working on an app that requires access to a user's location, even when your user has sent your app to the background, you might have noticed that when you ask the user for the appropriate permission, iOS 13 shows a different permissions dialog than you might expect. In iOS 12 and below, when you ask for so-called always permissions, the user can choose to allow this, allow location access only in the foreground or they can decide to now allow location access at all. In iOS 13, the user can choose to allow access once, while in use...

If you use Core Data in your apps, you might be aware that the larger and more complicated your set up becomes, the harder it is to debug. It's at this point where you might start to get frustrated with Core Data and its black-box kind of implementation. You might think that you simply have to trust that Core Data will do the ideal thing for your app. Furthermore, you might have a set up with multiple managed object contexts, each confined to its own thread. And when your app crashes sometimes, you think it's related to Core Data in...

One of iOS 13's more subtle, yet amazingly fun and powerful frameworks is CoreHaptics. With this framework, you can add tactile feedback to your app. When implemented correctly, this kind of feedback will delight and amaze your users. It will make your app feel alive like it's physically responsive to the touch input from your user. If you want to see what haptic feedback feels like in a real app, check out the CocoaHub app. It uses haptic feedback when you switch tabs in the app and in my opinion, this feels really nice. In this blog post you will...

Developers often need to store data on behalf of their users. Sometimes it’s a small amount simple data, other times it’s a lot of complex data. Maybe it’s highly sensitive data or maybe it’s less sensitive or even publicly available data. Choosing where to store this data is often not trivial, especially if you might be unaware of the options that are available to you, or the security considerations you need to keep in mind. In this week’s blog post I will show you several storage options that are available to you as an iOS developer, and I'll explain the...

A lot of apps rely on data from a remote source to display their content. Sometimes the content on the remote source changes regularly, sometimes it changes only sporadically. In all cases, your users will want to see the most up to date version of the information that you have to offer them, and in most cases, you will do your best to make sure that your users always have up to date information. There are many ways to make sure your users always see the latest data from your server. For example, you might be using web sockets if...

Apps send and receive data all the time. Some apps mostly read data from the network, others are more focussed on sending data to servers. Depending on your needs, you might need to be able to send data to a server as quickly as possible, or maybe you need to receive new data as soon as it’s available from a server. Every app has different needs and several mechanisms exist to streamline network communication. In this post week’s blog post, I will focus on one specific use of networking in apps. We’ll look at using web sockets to receive data...

December has always been a month of sharing for me. Sharing food and experiences with family, celebrating the end of what has (hopefully) been a wonderful year, reflecting and setting goals for the new year. And this year, I have decided to share something really special with the iOS community. In December I will publish a new blog post every day until Christmas eve. That's 24 blog posts in total. And since I want this whole endeavor to be about the community itself, I need your input. Send me messages on Twitter to let me know what you want to...