How to Fix ‘NSUnknownKeyException’, Reason: “… this class is not key value coding-compliant for the key X” Error in Xcode

How to Fix 'NSUnknownKeyException', Reason: "… this class is not key value coding-compliant for the key X" Error in Xcode

22 May 2024 Stephan Petzl Leave a comment Tech-Help

If you’re working with Xcode and encounter the error “NSUnknownKeyException, reason: ‘[<UIViewController 0x6e36ae0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key XXX'”, you’re not alone. This error typically occurs when there’s a mismatch between your Interface Builder (IB) connections and your code. In this article, we’ll explore the common causes and solutions to resolve this issue.

Common Causes and Solutions

1. Bad Connection in XIB or Storyboard

One of the most common causes of this error is a bad connection in your XIB or Storyboard file. This typically happens when you change the name of an IBOutlet property in your .h/.m file but forget to update the connection in IB.


  • Select the object in IB and go to the ‘Connections Inspector’.
  • Under ‘Referencing Outlets’, ensure that your object isn’t still connected to the old property name. If it is, click the small ‘x’ to delete the reference and build again.

2. Incorrect Class in XIB

This error can also occur if your view controller has the wrong class set in your XIB file.


  • Open your XIB file and ensure that the class of your view controller is set correctly.

3. Duplicate or Bad Outlets

Another common cause is having duplicate or bad outlets in your XIB or Storyboard file.


  • Control-click on the File’s Owner in the Interface Builder. If you see an exclamation mark next to any outlets, you need to fix them by removing or renaming them in your .h file.

4. Leftover User-Defined Runtime Attributes

If you have removed properties from your UIView extension but still have leftover user-defined runtime attributes in your Storyboard, this can also cause the error.


  • Right-click on your Storyboard file and open it as Source Code.
  • Search for the keyPath of the removed properties and delete the corresponding <userDefinedRuntimeAttributes> section.

Additional Tips

Sometimes, the error might be due to other less common issues, such as:

  • Having control-dragged and created an outlet or action but forgot to delete it.
  • Incorrect “Module” property in the Identity Inspector.
  • Issues with custom UITableViewCells or custom UIViewController subclasses.

Streamlining Your Testing Process

While fixing these issues can be time-consuming, it’s essential to ensure that your app functions correctly. However, spending too much time on debugging can take away from other critical development tasks. This is where automated testing tools like Repeato can be incredibly beneficial.

Repeato is a no-code test automation tool for iOS and Android that helps you create, run, and maintain automated tests for your apps. With its computer vision and AI capabilities, Repeato allows you to quickly edit and run tests, enabling developers to focus on creating a great product instead of spending time on creating and maintaining tests.

Learn more about how Repeato can help streamline your testing process by visiting our documentation and blog.

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