How to set theme on first and second activities programmatically?

Question

I'm create app with 2 activity and want set theme onclick button in first and second activity.

method setTheme() work only on first activity

    if(AppCompatDelegate.getDefaultNightMode() == AppCompatDelegate.MODE_NIGHT_YES) {
        setTheme(R.style.OLEDTheme);
    } else {
        setTheme(R.style.AppTheme);
    }
    Switch oledModeSwitch = (Switch) findViewById(R.id.OLEDSwitch);
    if (AppCompatDelegate.getDefaultNightMode() == AppCompatDelegate.MODE_NIGHT_YES) {
        oledModeSwitch.setChecked(true);
    }
    oledModeSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton compoundButton, boolean Check) {
            Intent intent = new Intent(getApplicationContext(), SettingsActivity.class);
            finish();
            if (Build.VERSION.SDK_INT >= 21) {
                overridePendingTransition(R.anim.from_alpha, R.anim.to_alpha);
            }
            startActivity(intent);
            if (Check) {
                Toast.makeText(getApplicationContext(), "Тема успешно активирована", Toast.LENGTH_SHORT).show();
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
            } else {
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
                Toast.makeText(getApplicationContext(), "Тема успешно дезактивирована", Toast.LENGTH_SHORT).show();
            }
        }
    });

Theme set only first activity, but I expect set on first and second activity

Answer 1

When you call setTheme() it only changes the theme for the Activity that made the call. If you want to change the theme for your entire application, then you should record the theme setting in SharedPreferences and then in each Activity you should read the current theme from SharedPreferences and call setTheme() in that Activity.