Subscribe to Dark Mode change event in Windows

Wait for Dark Mode change in Windows.md

Wait for Dark Mode change in Windows

This is a snippet I came up with that doesn't exist anywhere else on the net (so far). I think its the best way to programmatically detect dark mode change in Windows. Unlike other approaches, there's no busy-waiting/polling involved. Instead, we use the native event system to subscribe to the AppsUseLightTheme registry key change.

A big benefit of this approach is that theme change detection is almost instantaneous.

To run this in a loop, call this script, react to it's output, then call it again. An example script is provided.

wait-dark-mode-change.ps1

# Elevated prompts and WSL doesn't have current user's username/SID. Let's get it.
$username = Get-WMIObject -class Win32_ComputerSystem | select -ExpandProperty username
$SID = (Get-WMIObject -class Win32_UserAccount | ? {$_.Caption -eq $username}).SID

# The Registry value we want to listen to. 
$key = "Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize"
$value = “AppsUseLightTheme”
# Register-WmiEvent can't listen to HKEY_CURRENT_USER, hence the HKEY_USERS:\$SID\$key hack
$query = “SELECT * FROM RegistryValueChangeEvent WHERE Hive='HKEY_USERS' AND KeyPath='$SID\\$key' AND ValueName='$value'"

$event = Register-WmiEvent -Query $query -SourceIdentifier $value

try {
    Wait-Event -SourceIdentifier $value | Remove-Event
    echo (Get-ItemProperty -Path HKCU:$key).$value
    # prints 0 for dark mode, 1 for light
} finally {
    # trap Ctrl+C, cleanup.
    Unregister-Event -SourceIdentifier $value
}

wsl-dark-mode.sh

#!/bin/sh

cd $(dirname "$0") # directory containing both scripts.
while true; do
  MODE=
  case $(powershell.exe -NoProfile -Command ./wait-dark-mode-change.ps1) in
    0) 
      # react to dark mode
      MODE=dark
      ;;
    1)
      # react to light mode
      MODE=light
      ;;
  esac
  for s in /tmp/nvim-*.sock; do
    nvim --remote="$s" --remote-send ":set background=$MODE<CR>"
  done
done