Software⏱️ 3 min read📅 2026-06-03

How to Fix: libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)

Missing key exception in Swift iOS app, solution to fix NSUnknownKeyException error.

Quick Answer: Verify that all properties are defined and correctly set in the storyboard or programmatically.

📋 Table of Contents

  1. 💡 Why You Are Getting This Error
  2. ✅ Best Solutions to Fix It
  3. 💡 Conclusion

The error 'libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)' indicates that your app is crashing due to an unknown key-value coding issue. This problem affects developers who are using Swift and have added custom gestures or interactions to their apps.

This error can be frustrating because it prevents the user from experiencing the full functionality of the app, leading to a poor user experience. Fortunately, this issue can be resolved by identifying and fixing the incorrect key-value coding in the affected view controller.

💡 Why You Are Getting This Error

  • The primary cause of this error is that you have added a custom gesture or interaction to your app without properly implementing the necessary key-value coding. This can happen when using Swift and UIKit, especially when working with gestures or other user interactions.
  • An alternative reason for this issue could be that there are duplicate keys in your view controller's properties or variables, which can cause conflicts with the key-value coding system.

✅ Best Solutions to Fix It

Fixing the Issue by Reviewing Key-Value Coding

  1. Step 1: Step 1: Open the affected view controller and review its properties and variables to ensure that there are no duplicate keys. Use Xcode's built-in debugging tools, such as the debugger or the console log, to help identify any issues.
  2. Step 2: Step 2: Check the documentation for your custom gesture or interaction to ensure that it is properly implemented with key-value coding. Make sure that you have correctly set up the gesture recognizer and that there are no conflicts with other user interactions.
  3. Step 3: Step 3: Run the app again and test the gesture or interaction to ensure that it is working as expected. If the issue persists, use Xcode's debugging tools to identify any errors or warnings.

Alternative Fix Method: Using a Different Gesture Recognizer

  1. Step 1: Step 1: Consider using a different gesture recognizer that is not affected by key-value coding issues. There are several alternatives available, such as the UIGestureRecognizer or the UISwipeGestureRecognizer.
  2. Step 2: Step 2: Replace the custom gesture recognizer with the alternative gesture recognizer and test the app to ensure that it is working correctly. Make any necessary adjustments to the code to accommodate the changes.

💡 Conclusion

By following these steps, you should be able to fix the 'libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)' error in your Swift app. Remember to always review your code carefully and use Xcode's debugging tools to help identify any issues.

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