How to check if UserDefaults object is Empty

This will be a guide to check if UserDefaults has been set.
You will want to use this to make sure a value is not nil before you use it.

Here is a simple example in a ViewController class.

import UIKit

class ViewController: UIViewController {

  let theme = Themes() // custom class
  // 1. create user defaults
  let defaults = UserDefaults.standard 

  override func viewWillAppear() {
    super.viewWillAppear()

    // 2. Check if there is not an userDefaults object for theme
    if defaults.object(forKey: "theme") == nil {
      // 3. If there is not an object, then set a default. This will
      //    not be ran if there is an object.
      defaults.set("dark", forKey: "theme")
    }

    theme.setTheme(defaults.string(forKey: "theme"))
  }
}

Link to Gist

1. Create a constant to interact with the UserDefaults
2. Create an if statement to check if the object does not exist.
3. If the object does not exist, then set a default option. In the example above, I set it to dark.

There is no need to set the default option if the default object does exist because it has been set before.

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