iOS, Objective-C, Swift, Design and Whatever Comes in Mind

Overlooked API of the Day: NSCountedSet

Have you ever encountered the issue where you had a sequence of things, you needed the elements only once and must know what elements are duplicates? And how often they occure?

Take a look as NSCountedSet! For example when combining multiple collections (Sets), you can determine which elements are contained multiple times. That technique can be used to calculate the intersection of collections in a straight foreward way 🙃

Apples documentation can be found here.

"Overlooked API of the Day: NSCountedSet".

Advanced Debugging with Xcode and LLDB – Sharing my Notes

I watched the WWDC talk and I would like to share my notes with you. You can find the recording as well as the mentioned script over here.

  • Xcode debug tab can be opened when a breaktpoint is hit via settings > Running > Pauses > check “Show tab named: Debug”
  • po <variable> to get the value of a variable
  • expression <expression> (eg. expression didReachSelectedHeight = true) to execute code at the breaktpoint, useful to always take one branch of an if-else-statement
  • Breakpoints can execute a LLDB command and then continue running. When double-clicked, one can enter the command via “Add Action”. Enabling “Automatically continue after Evaluation” tells the debugger to execute the command and continue to run the program. Combined with the aforementioned point it is possible to (always) take one branch of an if-else-statement whilst debugging.
  • Shortcut the "change>compile>run" workflow by injecting the change directly through LLDB to your running code. Just add another breakpoint and add the code you just inserted to your source file here, too. expression <code you just updated> does the trick that helps to tighten the workflow.
  • Debug navigator > add symbol > "add symbolic breakpoint" to add breakpoints to framework's code. For example [UILabel setText:] to add a breakpoint that hits every time a labels text is changed. Resolving the methods name succeeded when a text like “in UIKitCore” appears beside your new breakpoint. When this breakpoint hits, one can
    • po $arg1 to print the receiver of the Objective-C message (the UILabel in this case).
    • po (SEL)$arg2 to print the selector that is sent to the object.
    • po $arg3 to print the first argument passed into the method.
  • In a breakpoint, another breakpoint can be set dynamically with breakpoint set --one-shot true -name [UILabel setText:] (one shot breakpoint: only exists until it is triggered and then removed). Useful to “enable” a breakpoint only after a given part of code is executed, for example when the text of a label is updated in the following code.
  • Change the instruction pointer while the execution is paused by grabbing the grab-handle left besides “Thread 1: breakpoint…” in the green bar.
  • thread jump --by 1 tells the debugger to jump one code line ahead when the breakpoint is hit. Useful to skip code or execute different code by adding another action to the breakpoint.
  • Adding a breakpoint to a variable declaration will pause execution every time the variable is accessed.
  • po <variable> uses the debugDescription method of an object, p <variable> is more verbose in some cases.
  • Watchpoints pause the execution every time the value of a variable is changed. They can be added by right-clicking on the variable in the left side of the debugger pane. They appear below regular breakpoints in Xcode's navigator.
  • expression -l objc -O -- [’self.view' recursiveDescription] will print the description of the view as well as all contained subviews. It is an internal Objective-C method and can not be called using Swift. “’“ around self.view will tell the debugger to evaluate this expression first.
  • Printing the content of memory addresses like po 0x67aef7891 will not work using swift. One must use expression -l objc -O -- po 0x67aef7891​. A handy way to create a shortcut is by typing command alias poc expression -l objc -O --. Now it is possible to type poc 0x67aef7891.
  • In Swift, you can also use po unsafeBitcast(0x2d34bd25, to: YourView.self) instead of using Objective-C evaluation. You can even chain expressions together, like po unsafeBitcast(0x2d34bd25, to: YourView.self).center.y = 300. When a UIView property is changed in this way, one need to tell CoreAnimation to update its frame buffer, as the execution is currently paused: expression CATransaction.flush()
  • A python script that changes properties of the view using the debugger is presented. To use commands provided by this script, open ~/.lldbinit in you home directory and add command script import ~/ You can also define your previously created aliases there.
  • Using the nudge tool, one can live update positions of views by using the debugger.

"Advanced Debugging with Xcode and LLDB – Sharing my Notes".

Open Source: FeedbackController

The Taptic Engine was introduced in Apples iPhone 7. It not only made possible to replace the mechanical home button but it also introduced API for developers. Through this API it became possible to give the user a subtle mechanical feedback about what is happening on screen.

For example an app can combine user interactions (like tapping a button, fading a slider oder flipping a view) with a light shake of the phone.

Even more sophisticated feedback types are possible. A notification can be combined with the according haptic feedback and then the user can literally feel if a task was successful or not.

My new open source project makes the usage of the mentioned API easier. You can find the project over here at GitHub. As always, I would love to hear feedback from you 🤗.

This blogpost describes the usage of the haptic feedback API and explains the approach of my new project. If it makes live easier for you, feel free to use it. Otherwise it could provide a reference implementation for you.


To integrate the haptic feedback, one must use UIFeedbackGenerator. This superclass is derived by three different subclasses: UIImpactFeedbackGenerator, UINotificationFeedbackGenerator and UISelectionFeedbackGenerator.

These three subclasses can be used for three different types of feedback:

  1. A single tap-like feedback provided by UIImpactFeedbackGenerator
  2. A more complex feedback to indicate that a task has completed (successfully / erroneous) or that a warning occurred by using UINotificationFeedbackGenerator
  3. A single tap that implies a change in the users selection, for example when a switch is used or an image snaps into place, provided by UISelectionFeedbackGenerator

In any case, the Taptic Engine must be transitioned into its active state, by calling prepare() on any of the mentioned subclasses. To align the UI interaction or even sounds with the haptic feedback, prepare should be called about one or two seconds in advance.

What FeedbackController does

As it turns out, the API is not as straight forward as it could be. For example, the type of the notification-feedback is set when the feedback should fire.

Then again, the type of an impact feedback must be set during the prepare state.

In addition to that, the API is only available on iPhone 7 or newer, running iOS 11 or higher. Prior to using the described APIs, one must perform availability checks. As a reference to the UIFeedbackGenerator must be held strongly and calls to prepare and perform can occur in many places of your app, those checks need to be implemented quite frequently.

That is where FeedbackController comes into play. It simplifies the calls, needed to perform haptic feedback. It eliminates the need for the developer to keep in mind where the types of feedback can be configured.

In addition to that, it comes with easy to use extensions of UIViewController. They make it possible to use feedback everywhere in the app by two simple method calls:

image showing the usage of FeedbackController

However, a call to prepareFeedback(for:) should be made as early as possible so that the Taptic Engine can be powered on. Please see the example project for further details.

How to use it

If you integrate FeedbackController using CocoaPods, you need to import FeedbackController first.

When you expect that a user interaction will take place in the next couple of seconds, call prepareFeedback(for:). In doing so, the Taptic Engine will be powered on and is ready for your feedback. The timing is not as critical as might have guessed and it turned out that preparing the Taptic Engine in viewDidAppear(_:) is sufficient.

However, the type of feedback is determined by the call to prepareFeedback(for:).

Secondly, a feedback needs to be performed. To do so, just call

  1. hapticFeedbackImpactOccured() for a impact feedback.
  2. hapticFeedbackNotificationOccured(with:) for a notification feedback, specifying the type of said notification.
  3. hapticFeedbackSelectionChanged() for a selection feedback.

When you are done with the feedback, call doneWithHapticFeedback() to allow the Taptic Engine going back to its idle state.


You can install it by using CocoaPods or just by copying the FeedbackController.swift file.
Again, here is the link to the project.

Please let me know what you think about it.

"Open Source: FeedbackController".