Coding⏱️ 2 min read📅 2026-05-31

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

Fixing NSUnknownKeyException error in Swift

Quick Answer: Update your gesture recognizer to use the correct key, and ensure that the property name matches the actual key used to store it in the view controller's dictionary.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🚀 How to Resolve This Issue
  3. 💡 Conclusion

The error 'libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)' indicates that there is a problem with the key-value coding compliance in your app. The specific error message you're seeing, 'this class is not key value coding-compliant for the key sfdfa', suggests that you have accidentally added a property or outlet to your ViewControllerTwo instance without properly declaring it as optional.

🔍 Why This Happens

  • [Cause]

🚀 How to Resolve This Issue

Method 1: Use Optional Type for Properties or Outlets

  1. Step 1: Open your ViewControllerTwo.h file and declare any properties or outlets as optional types (e.g., @property (nonatomic, weak) IBOutlet UIView *sfdfa;).

Method 2: Use the 'optional' Keyword

  1. Step 1: Open your ViewControllerTwo.h file and use the 'optional' keyword to declare properties or outlets (e.g., @property (nonatomic, weak) IBOutlet UIView *sfdfa optional;).

💡 Conclusion

By following these steps, you should be able to resolve the 'this class is not key value coding-compliant for the key sfdfa' error and ensure that your app runs smoothly on the iPhone simulator.

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