Added reset button but slightly working as intended.

Author: vincetzr

app/src/main/java/org/schabi/newpipe/settings/AppearanceSettingsFragment.java

@@ -80,22 +80,4 @@ private void applyThemeChange(final String beginningThemeKey,
             ActivityCompat.recreate(getActivity());
         }
     }
-
-    public void resetToDefault() {
-        final String themeKey = getString(R.string.theme_key);
-        final String startThemeKey = defaultPreferences
-                .getString(themeKey, getString(R.string.default_theme_value));
-        final String autoDeviceThemeKey = getString(R.string.auto_device_theme_key);
-        if (startThemeKey.equals(autoDeviceThemeKey)) {
-            applyThemeChange(startThemeKey, themeKey, autoDeviceThemeKey);
-            } else {
-            if (startThemeKey.equals(R.string.light_theme_key)) {
-                removePreference(getString(R.string.light_theme_key));
-            } else if (startThemeKey.equals(R.string.dark_theme_key)) {
-                removePreference(getString(R.string.dark_theme_key));
-            } else {
-                removePreference(getString(R.string.black_theme_key));
-            }
-        }
-    }
 }

app/src/main/java/org/schabi/newpipe/settings/ResetSettingsFragment.java

@@ -2,13 +2,22 @@
 
 import android.os.Bundle;
 
+import androidx.core.app.ActivityCompat;
+
+import org.schabi.newpipe.R;
+import org.schabi.newpipe.util.Constants;
+import org.schabi.newpipe.util.ThemeHelper;
+
 public class ResetSettingsFragment extends BasePreferenceFragment {
 
-    private AppearanceSettingsFragment appearanceSettings;
     @Override
     public void onCreatePreferences(final Bundle savedInstanceState, final String rootKey) {
         addPreferencesFromResourceRegistry();
 
-        appearanceSettings.resetToDefault();
+        // reset appearance to light theme
+        defaultPreferences.edit().putBoolean(Constants.KEY_THEME_CHANGE, true).apply();
+        defaultPreferences.edit().putString(getString(R.string.theme_key),
+                getString(R.string.light_theme_key)).apply();
+        ThemeHelper.setDayNightMode(requireContext(), "light_theme");
     }
 }

app/src/main/java/org/schabi/newpipe/settings/SettingsResourceRegistry.java

@@ -41,6 +41,7 @@ private SettingsResourceRegistry() {
         add(UpdateSettingsFragment.class, R.xml.update_settings);
         add(VideoAudioSettingsFragment.class, R.xml.video_audio_settings);
         add(ExoPlayerSettingsFragment.class, R.xml.exoplayer_settings);
+        add(ResetSettingsFragment.class, R.xml.main_settings);
     }
 
     private SettingRegistryEntry add(

app/src/main/res/xml/reset_settings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+
+</PreferenceScreen>