Whoever has worked with UITable- or UICollection-Views in the past will have seen error messages like the following probably more often:

Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (22) must be equal to the number of items contained in that section before the update (34), plus or minus the number of items inserted or deleted from that section (23 inserted, 5 deleted) and plus or minus the number of items moved into or out of that section (3 moved in, 5 moved out).

UICollection- and UITableViews

Because RxSwift and Combine have so much in common I thought it would be a great idea to adapt the things I know about RxSwift and use them to create something new.

This is an article based on one of my most successful articles here on Medium (Learn and Master Rx-Swift). More than 140.000 Impressions so far. That’s Amazing, thank you so much.

Remote Push notifications enable developers to present information to their users outside the app and to redirect them to the app if necessary. Important events will arrive in the form of badges, sounds or banners. But be careful here, too many push notifications may lower the retention and deter your users. When and how push notifications are displayed should be well considered, inflationary and unimportant notifications can mean death for a good app.

In the last iOS versions the range of functions around Push Notifications has grown enormously. It is now possible to define your own actions, to manipulate the…

Anyone who has ever implemented dynamic lists in iOS will probably know that the official approach has some difficulties. Datastore and view layer have to be synchronized manually and during the update a certain order should be kept to avoid crashes. In addition, the classical approach is tempting to encapsulate the logic of the different cells in a large data source rather than separating them sensibly. To prevent these problems IGListKit was created. A framework developed by the Instagram team . What exactly IGListkit does and how it can be used, I will show you in the following sections.


Every programmer should have heard of Rx. Whether it happened at the last developer conference or while reading a fresh blog article like this one 😎. It is almost impossible not to have heard of it, but what exactly is Reactive Programming? Let’s take a look on the Internet:

In computing, reactive programming is a programming paradigm oriented around data flows and the propagation of change. This means that it should be possible to express static or dynamic data flows with ease in the programming languages used, and that the underlying execution model will automatically propagate changes through the data…

Yay, my first Pod is available for everyone. Jelly 1.0, a Viewcontroller-Transition-Animation framework that is super easy to use. No need to create your own Presentation-Controllers or Animator-Objects to realize fancy and rich transtions. Jelly will do the heavy lifting for you.

I always wanted to have a public Github repository other people can contribute to and I found myself writing custom Viewcontroller-Transition-Code over and over again. So wouldn’t it be a great idea to create an easy to use Pod for that?

This is the story about how I created Jelly 1.0

Hey Followers, this is the first issue of Swift Bites. These series will focus on Swift features and problem-solving techniques using Swift. I will examine everything interesting I discover during my daily work as an iOS Developer. I will try to keep these posts a lot shorter than my regular Articles so that I can release them more frequently.

An Optional Feature I didn't know so far

Lately, I was working on the Swift 3.0 Port of our App. So at first I triggered the automatic Swift conversion. A lot of stuff was altered automatically by the converter. …

If you are new to swift and to the concept of Optionals it may seems a little bit strange to have a special type for representing something or nothing, but if you get the hang of it, it will come really handy in a lot of situations.


You should understand Swift Enums before continuing with this article. If you don't have any clue what an Enum is, please take the time to read through the official documentation.


Basically, an Optional is an Enum with 2 cases and one of the cases has an associated value attached to it.

  • .Some(Wrapped)
  • .None

I am developing Apps for more than 3 years now and 1 thing that still annoys me is Code Signing and Provisioning in iOS. What are Signing Identities? Why do I need to create Provisioning Profiles and care about such things as a developer? If you don’t have any good answers for those questions and really don’t want to read through the Apple Docs, this hopefully is the article that exposes the whole process for you and for me as a reference in less than 5 Minutes.

I am sure many of you can learn things fast just by reading…

Last Update 27.02.2017

This is a curated list of iOS Development Tools, Websites, Services and Frameworks I am currently using.


  • A modular plugin system for your iOS Apps called Fabric
  • Testflight is a native beta test distribution framework
  • Smooch is a great messaging SDK I am currently using to get direct feedback from my users.
  • Mobile Analytics with Mixpanel
  • I use Trello to manage my private projects
  • When working in a Team, I prefer using a tool like JIRA directly connected with the Repository in conjunction with SCRUM and Gitflow Workflow


  • Continuous Delivery made easy using Fastlane. It automatically builds…

Sebastian Boldt

Creative Head, iOS Developer @ Immowelt, DJ/Producer from Hamburg. Creator of HabitBe, a weekly Habit Tracker written in SwiftUI. https://www.sebastianboldt.com

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store