How to switch themes (night mode) without restarting the activity?

Question

I have made a few apps that support multiple themes, but I always had to restart the app when user switches theme, because setTheme() needs to be called before setContentView().

I was okay with it, until I discovered this app. It can seamlessly switch between two themes, and with transitions/animations too!

Please give me some hints on how this was implemented (and animations too). Thanks!

Answer 1

@Alexander Hanssen's answer basically has answered this... Don't know why it was not accepted... Maybe because of the finish()/startActivity(). I voted for it and I tried to comment but cannot...

Anyway, I would do exactly what he described in terms of styles.

<style name="AppThemeLight" parent="Theme.AppCompat.Light">     <!-- Customize your theme here. -->     <item name="android:windowAnimationStyle">@style/WindowAnimationTransition</item> </style> <style name="AppThemeDark" parent="Theme.AppCompat">     <!-- Customize your theme here. -->     <item name="android:windowAnimationStyle">@style/WindowAnimationTransition</item> </style> <!-- This will set the fade in animation on all your activities by default --> <style name="WindowAnimationTransition">     <item name="android:windowEnterAnimation">@android:anim/fade_in</item>     <item name="android:windowExitAnimation">@android:anim/fade_out</item> </style> 

But instead of finish/start with new intent:

Intent intent = new Intent(this, <yourclass>.class); startActivity(intent); finish(); 

I would do:

@Override protected void onCreate(Bundle savedInstanceState) {      // MUST do this before super call or setContentView(...)     // pick which theme DAY or NIGHT from settings     setTheme(someSettings.get(PREFFERED_THEME) ? R.style.AppThemeLight : R.style.AppThemeDark);      super.onCreate(savedInstanceState); }  // Somewhere in your activity where the button switches the theme btn.setOnClickListener(new View.OnClickListener() {     @Override     public void onClick(View v) {          // decide which theme to use DAY or NIGHT and save it         someSettings.save(PREFFERED_THEME, isDay());          Activity.this.recreate();     } }); 

The effect is as shown in the video...