<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:padding="16dp">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true">

        <SeekBar
            android:id="@+id/brightnessControl"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:progress="50"
            android:max="100"
            android:layout_marginTop="20dp"
            android:layout_marginBottom="6dp"/>

        <TextView
            android:id="@+id/brightnessValue"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/brightnessControl"
            android:layout_centerInParent="true"
            android:text="0.5"
            android:textSize="22sp"
            android:textColor="#000000"
            android:padding="16dp"
            android:layout_marginTop="20dp"/>
    </RelativeLayout>

</RelativeLayout>
                                    
                                  

                                    
                                        import android.os.Bundle;
import android.view.WindowManager;
import android.widget.SeekBar;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    SeekBar seekBar;
    TextView textView;
    Float backLightValue = 0.5f;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        seekBar = findViewById(R.id.brightnessControl);
        textView = findViewById(R.id.brightnessValue);

        seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                backLightValue = (float) progress / 100;
                textView.setText(String.valueOf(backLightValue));
                WindowManager.LayoutParams layoutParams = getWindow().getAttributes();
                layoutParams.screenBrightness = backLightValue;
                getWindow().setAttributes(layoutParams);
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });
    }
}
                                    
                                  

                                      
                                        import android.os.Bundle
import android.view.WindowManager
import android.widget.SeekBar
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    private lateinit var seekBar: SeekBar
    private lateinit var textView: TextView
    private var backLightValue: Float = 0.5f

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        seekBar = findViewById(R.id.brightnessControl)
        textView = findViewById(R.id.brightnessValue)

        seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
            override fun onProgressChanged(seekBar: SeekBar, progress: Int, fromUser: Boolean) {
                backLightValue = progress / 100f
                textView.text = backLightValue.toString()
                val layoutParams = window.attributes
                layoutParams.screenBrightness = backLightValue
                window.attributes = layoutParams
            }

            override fun onStartTrackingTouch(seekBar: SeekBar) {}

            override fun onStopTrackingTouch(seekBar: SeekBar) {}
        })
    }
}