How to use dark mode in simulator iOS 13?

In Settings, scroll down to Developer and then Dark Appearance…

Update

In addition to the above, there are now many other ways to enable dark appearance in the simulator, as shown in the many great answers below.

• Change Environment Overrides from Xcode (@AshCameron)

• Toggle Appearance ⇧⌘A from the Simulator menu (@Shredder2794)

• Update from the command line using xcrun simctl ui booted appearance … (@blackjacx, @tadija)

• Programmatically using overrideUserInterfaceStyle = .dark (@thisIsTheFoxe)

• Specify UIUserInterfaceStyle in your info.plist (@DhavalGevariya)

• Use SimGenie from Curtis Herbert…  https://simgenie.app

You can toggle the interface mode (i.e. Light / Dark) as well as adjust dynamic type setting on the fly (when the simulator is running) like this:

You can use the "Toggle Appearance" (ShiftCommandA) setting from the Simulator menu:

Simulator > Features > Toggle Appearance ⇧⌘A

Automated Appearance Change 🦉

Xcode 11.4 🌟

Apple released a powerful Xcode update which contains some useful things for this topic. Appearance can now be selected directly in the simulator. Just select Features > Toggle Appearance or ⇧+⌘+A. The automatic appearance switching could stil be important, e.g. for automated screenshot tests on the command line. The script becomes easy like this when using Xcode 11.4:

device_ids=("C741F3CD-FDAC-49EA-A4DB-7F797B97291E" "428183B6-3EB8-4D36-9938-9D07C141BF49")

# The value to use is now just 'dark' or 'light'
appearance=dark

for device in "${device_ids[@]}"; do
  xcrun simctl boot $device
  xcrun simctl ui $device appearance $appearance
done

No more simulator killing or re-setting needed which is a huge performance win. Also no fiddling around with any plist tools anymore - ever. keep in mind that you have to use device ids that are available in the runtime you use. Find them out using xcrun simctl list.

See also my complete script: https://github.com/Blackjacx/Scripts/blob/master/set-simulator-style.sh

Xcode 11.3

There is a way using the command line to switch a simulator between light and dark mode. If you have an array with your device IDs you can do the following:

device_ids=("C741F3CD-FDAC-49EA-A4DB-7F797B97291E" "428183B6-3EB8-4D36-9938-9D07C141BF49")

# Determine the plist value for the desired style: "dark" -> 2 / "light" -> 1
style=2

for device_id in "${device_ids[@]}"; do
  plist_path="${HOME}/Library/Developer/CoreSimulator/Devices/${device_id}/data/Library/Preferences/com.apple.uikitservices.userInterfaceStyleMode.plist"  
  printf '\n%s' "Set style $style for device $device_id ($plist_path)"

  killall "Simulator"
  xcrun simctl shutdown booted
  xcrun simctl erase $device_id

  # Crate the plist since it might not be available after erase
  [[ ! -f "$plist_path" ]] && /usr/libexec/PlistBuddy -c "save" $plist_path  
  # Set the style mode
  plutil -replace UserInterfaceStyleMode -integer $style $plist_path
done

If you want to specify device names in your script - since device IDs are different on different machines - you can also easily find the id's of them using the following bash code:

device_names=("iPhone SE" "iPhone 8" "iPhone 11 Pro" "iPhone 11 Pro Max")
device_ids=()

for name in "${device_names[@]}"; do
  id=$(xcrun simctl list --json | jq ".devices | .[] | .[] | select(.name == \"$name\") | .udid" | cut -d\" -f2)
  device_ids+=("$id")
done

printf '%s\n' "${device_ids[@]}"

Alternatively, you can also switch the appearance programmatically (docs):

override func viewDidLoad() {
    super.viewDidLoad()
    #if DEBUG
    // change the appearance only while testing  
    overrideUserInterfaceStyle = .dark
    #endif
}