Android App theme is not changing when I press the system back button

Question

I know there are similar questions asked but I couldn't find a proper answer.

Current Status of app

Right now I have implemented the two themes AMOLED / Day / System Default and everything is working fine. To switch the theme of the app I am using the following command

setTheme(R.style.Theme_RandomApp_Day);

Problem

When I am switching the theme by the above command [settings.java], the theme changes normally and when I press the back arrow on the toolbar of the app [In app toolbar, not system back button], parent activity launches [MainActivity.java] and the theme of this activity is the one that I have set in settings activity. Till now the functionality is what is expected.

But when I perform the same task [changing the theme in settings.java] the theme in settings.java changes but this time with the smartphones inbuilt back button when pressed the theme in the MainActivity.java does not change .

Answer 1

To solve the problem as drjansari I used the following code

@Override
    public void onBackPressed() {
        super.onBackPressed();
        finish();
        startActivity(new Intent(settings.this, MainActivity.class));
    }

And It worked but now I have another problem XD