The latest articles on DEV Community by Lexip (@xlexip). https://dev.to/xlexip https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.us-east-2.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F1212423%2F5a4fa651-37fa-4675-ba7b-4f18adb2fca5.png https://dev.to/xlexip en Lexip Sat, 03 Jan 2026 11:56:10 +0000 https://dev.to/xlexip/i-built-an-open-source-android-app-that-switches-dark-mode-based-on-ambient-light-adaptive-theme-2fd3 https://dev.to/xlexip/i-built-an-open-source-android-app-that-switches-dark-mode-based-on-ambient-light-adaptive-theme-2fd3 <blockquote> <p><strong>Update, August 2026:</strong> Adaptive Theme now includes Wallpaper Theme Sync and an optional blurred lock-screen wallpaper.</p> </blockquote> <p>Android’s built-in automatic dark mode is usually based on a schedule or sunset. That is often a poor proxy for the actual lighting around you: a bright room at night may call for light mode, while a dark room during the day may not.</p> <p>I built <strong>Adaptive Theme</strong>, a free and open-source Android app that switches the system-wide light and dark theme based on the device’s physical ambient light sensor.</p> <p>This is an Android app, not a Flutter theming library. Its package name is <code>dev.lexip.hecate</code>.</p> <h2> The design goal </h2> <p>The app should react to real-world light conditions without continuously monitoring the sensor or switching the theme while someone is actively using their phone.</p> <p>The solution is an event-driven screen-on flow:</p> <ol> <li>The screen turns on.</li> <li>Adaptive Theme briefly samples the ambient light sensor.</li> <li>It checks whether the sensor is likely obstructed, for example by a hand or pocket.</li> <li>The measured value is compared with a configurable lux threshold.</li> <li>If required, the Android system theme is changed before the user starts interacting.</li> </ol> <p>The sensor is not continuously polled. After the short screen-on measurement, it stops.</p> <p>This also means the app deliberately does not change the system theme in the middle of a session. Some apps handle a live theme change poorly, so screen-on is a predictable and less disruptive moment for it.</p> <h2> Features </h2> <ul> <li>Automatic system-wide light and dark mode based on ambient light</li> <li>Custom lux threshold and presets</li> <li>Night Lock for keeping dark mode enabled during a chosen time window</li> <li>Wallpaper Theme Sync with separate wallpapers for light and dark mode</li> <li>Optional blur effect for the lock-screen wallpaper</li> <li>Quick Settings tile</li> <li>Material You interface</li> <li>Android 14+ smartphones</li> <li>Free, open source, and ad-free</li> </ul> <h2> The Android permission problem </h2> <p>Changing the Android system theme requires <code>WRITE_SECURE_SETTINGS</code>, which regular apps cannot grant to themselves through the usual Android permission dialog.</p> <p>Adaptive Theme has a guided setup for the one-time grant:</p> <ul> <li> <strong>WebADB:</strong> use another device through the browser-based setup tool</li> <li> <strong>Shizuku:</strong> grant the permission on-device</li> <li> <strong>Root:</strong> grant it through the app on a rooted device</li> <li> <strong>Manual ADB:</strong> run the displayed command from a computer</li> </ul> <p>Once granted, the permission persists across reboots. Shizuku, root, or an ADB connection is not required for normal operation afterwards.</p> <p>Android 14 is the minimum supported version because this screen-on sensor architecture depends on APIs that are not available on older Android releases.</p> <h2> Tech stack </h2> <p>The app is built with:</p> <ul> <li>Kotlin</li> <li>Jetpack Compose and Material 3</li> <li>MVVM</li> <li>Kotlin Coroutines and Flow</li> <li>DataStore</li> </ul> <h2> Links </h2> <ul> <li> <strong>Google Play:</strong> <a href="https://play.google.com/store/apps/details?id=dev.lexip.hecate" rel="noopener noreferrer">https://play.google.com/store/apps/details?id=dev.lexip.hecate</a> </li> <li> <strong>FOSS APK / releases:</strong> <a href="https://github.com/xLexip/Adaptive-Theme/releases" rel="noopener noreferrer">https://github.com/xLexip/Adaptive-Theme/releases</a> </li> <li> <strong>Source code:</strong> <a href="https://github.com/xLexip/Adaptive-Theme" rel="noopener noreferrer">https://github.com/xLexip/Adaptive-Theme</a> </li> <li> <strong>Feature video:</strong> <a href="https://www.youtube.com/watch?v=8zCZFw_wx-Y" rel="noopener noreferrer">https://www.youtube.com/watch?v=8zCZFw_wx-Y</a> </li> </ul> <p>Feedback, bug reports, feature ideas, and contributions are welcome.</p> android opensource kotlin jetpackcompose