Clearing UserDefaults during debug builds from Xcode

README.md

Use a UUID marker on each build (works even if build number doesn't change)

If you want UserDefaults to clear every time you install a new Debug build via Xcode, regardless of version or build number, you can inject a unique marker that changes on every build.

🔧 1. In your Build Settings (not Info.plist), add a custom build variable:

Go to:

Build Settings → User-Defined → click +

Add:

Key: BUILD_ID
Value: ${CURRENT_PROJECT_VERSION}-${CURRENT_TIME}

Or just:

BUILD_ID = $(CURRENT_PROJECT_VERSION)-$(SOURCE_ROOT)

Then expose it to your code via Build Settings → Swift Compiler → Custom Flags:

Other Swift Flags: -D BUILD_ID="your-build-id-here"

But this is clunky.

Generate a random UUID at build time and bake it into the app (simpler)

Use a script to write a random UUID into Info.plist every time you build:

Add a Run Script Phase in Xcode

In your project:

Target → Build Phases → "+" → "New Run Script Phase"

Paste:

uuid=$(uuidgen)
defaults write "${SRCROOT}/Info" BuildUUID "$uuid"

Or if you're managing Info.plist in Xcode directly:

/usr/libexec/PlistBuddy -c "Set :BuildUUID $(uuidgen)" "${TARGET_BUILD_DIR}/${INFOPLIST_PATH}"

clearUserDefaults.swift

import UIKit

class AppDelegate: NSObject, UIApplicationDelegate {
    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {

        #if DEBUG
          let buildUUIDKey = "BuildUUID"
          let defaults = UserDefaults.standard
          let currentUUID = Bundle.main.infoDictionary?[buildUUIDKey] as? String
          let lastClearedUUID = defaults.string(forKey: "lastClearedUUID")

          if currentUUID != lastClearedUUID {
              print("🧹 New Debug Build Detected – Clearing UserDefaults")
              if let bundleID = Bundle.main.bundleIdentifier {
                  defaults.removePersistentDomain(forName: bundleID)
              }
              defaults.set(currentUUID, forKey: "lastClearedUUID")
          }
        #endif
      
        return true
    }
}

nukeUserDefaults.swift

import UIKit

class AppDelegate: NSObject, UIApplicationDelegate {
    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {

        // force-clear on every debug launch (this wipes every launch, not just on install/update)
        #if DEBUG
        UserDefaults.standard.removePersistentDomain(forName: Bundle.main.bundleIdentifier!)
        #endif

        return true
    }
}