Swift - UserDefaults 设置未保存在框架内

Question

I have a framework that is generating a device UUID once and saving it using UserDefaults. The app has access to the UserDefaults and everything works as expected. However, the framework is not accessing UserDefaults in some cases. I sorted this out on an iPhone 8 using the synchronize() method:

  func getDeviceID() -> String {
      if let device = UserDefaults.standard.object(forKey: "DeviceID") as? String {
           return device
       } else {
           let device = UUID().uuidString
           UserDefaults.standard.set(device, forKey: "DeviceID")
           UserDefaults.standard.synchronize() // this line helped with an iPhone 8
           return device
       }
   }

However, on an older iPhone SE 1st generation the issue comes back. First, why is this happening at all, and why is the synchronize() method seemingly helping in a newer device? (Both phones are running iOS 13) Are there any known limitations when accessing UserDefaults from within a framework?

Answer 1

If it is failing when you're reading data right after writing the deviceId to UserDefaults Then it could be related to how UserDefaults actually stores the data to disk.

The actual write to disk is asynchronous and batched automatically by NSUserDefaults. Check this

So there's a chance that it is slower for older devices running new iOS versions.