Android-night-mode Questions

I implemented night mode in my app.user can change the night mode settings in profile activity.the order of activities are as follows.

I am using switch preference in my preference activity to change app theme but it is not working properly . i can't figure out what am i doing

I have this activity (subclass of appcompatactivity): <activity

I have a requirement that when a switch is clicked, i need to invert the mode from dark to light and vice versa respectively. but the twist part