Introducing: Simple Call Blocker

Recently I released a new iOS app: Simple Call Blocker.

It is a free utility that lets you block unwanted calls to your iPhone. Unlike most of the call blockers on iOS, it allows you to block whole ranges of numbers, such as your phone number’s extension, for free. You may also whitelist numbers, ranges of numbers, or all your contacts’ phone numbers, so that they will not be blocked by this app, even if they are in the blacklist.

The Simple Call Blocker website explains it in more detail.

Why did I write it?

I wanted to write a small, relatively simple app that would allow me to explore the following things:

  1. iOS application architecture: I have been reading books and articles on iOS application architecture, and decided to create a new app to practice new techniques, such as the use of coordinators for navigation rather than storyboard segues, that I have been learning.
  2. algorithms and operation queues: I started the app by writing some simple algorithms for creating sequential phone number ranges to load into an iOS CallKit directory extension. The last thing I wrote was a multi-threaded operation queue for processing blacklist and whitelist rules and refreshing the iOS call directory extension that actually blocks the phone numbers.
  3. Core Data: I avoided learning Core Data for years; that changed with this app.

Overall, the app was a lot of fun to write. It took me about a month in my after-hours “free time” to create. The overall process has made me a better iOS app developer. I’m excited to bring forward the skills and concepts I developed on this project to future work.

Why a call blocker app?

I started getting neighbor spam calls, so I downloaded nearly all the iOS call blocking apps I could find. There were fewer such apps than I thought there would be, all of them seemed amateurish in some way or another, and all of them (as of a month ago) required an in-app purchase or a subscription to block my neighborhood exchange. I wasn’t willing to pay for that feature in any of the apps that I tried, because all of those apps weren’t that good. Plus, blocking an exchange, or a continuous range of numbers, is pretty trivial, so I thought I could create an app that did that, and offer it for free to people.

So is this just a “practice” app?

No. It is well-written and works as well as iOS’s Call Directory extensions allow it to. It has a rough edge or two, though, in that it reloads its directory extension and reports success or errors back to the users, rather than trying to prevent the user from ever encountering an error from being reported by the directory extension loading process.

What that means is that you can ask Simple Call Blocker to block more numbers that iOS will allow—there is an undocumented limit—and the app has to wait for the CallKit Directory Extension’s load process to report success or failure before it can tell the user what is going on. I decided not to try to impose limits on how many numbers could be blacklisted, but instead allow the app to report the Directory Extension’s errors, if any, back to the user. I figure that the undocumented maximum number of blocked phone numbers probably is dependent on whatever hardware is in your phone, and probably is increasing in every new iPhone model.

The Simple Call Blocker directory extension is coded extremely conservatively, and it optimized for very low RAM and system usage. If iOS cannot load it, it is because the user put too many numbers in the blacklist, or because it is still loading numbers from a prior attempt.

Releasing the app for free, I think, makes it OK that it may not work exactly as users expect it to.

What is the future of this app?

I plan to support it through various iOS releases, but otherwise not improve it too much. After all, it is a free app.

I want to know more!

Go ahead and download the app in the iOS App Store (it’s free!), and check out the FAQ online.