Software⏱️ 3 min read📅 2026-05-31

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

Xcode error fix for NSUnknownKeyException

Quick Answer: Ensure your outlet is connected to the correct property in Interface Builder and check that the class conforms to KVC-compliant protocols.

📋 Table of Contents

  1. 🛠️ Step-by-Step Verified Fixes
  2. 🎯 Final Words

The "NSUnknownKeyException" error occurs when you're trying to set a value for a key that doesn't exist in your object. In the context of Xcode, this usually happens when you're linking a UILabel with an IBOutlet created in your class.

🛠️ Step-by-Step Verified Fixes

Method 1: Connecting the Outlet

  1. Step 1: Open your Xcode project and select the file that contains the UILabel you're trying to link.
  2. Step 2: In the Identity Inspector, make sure the Label is set as a User-Defined Type (UDT) by clicking on the 'Type' dropdown menu and selecting 'Custom Class'.
  3. Step 3: If you haven't already, create a new Swift file in your project and give it a name that matches the class name of your UILabel (e.g. "Label").
  4. Step 4: In this new Swift file, add the following code: `@objc public class Label: UILabel { }` This will allow Xcode to recognize your custom class.

Method 2: Using Storyboards

  1. Step 1: Open your Xcode project and select the file that contains the UILabel you're trying to link.
  2. Step 2: In the Storyboard, select the UILabel and control-drag it to the view controller where you want it to appear.
  3. Step 3: When prompted, choose 'Create Outlet' and give your outlet a name (e.g. "label").

🎯 Final Words

By following these steps, you should be able to resolve the "NSUnknownKeyException" error and successfully link your UILabel with an IBOutlet. If you continue to experience issues, try restarting Xcode or checking for any other potential causes.

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