How to change screen brightness programmatically

Posted By Android Guru on May 1, 2013 | 7 comments

This post will explain you how to change the current system brightness with a seek bar on Android devices. The application which we are going to develop will work only on real devices, because it is impossible to see the brightness changes on the emulator.

One thing you must know is that Android system brightness value is applied to the screen’s backlight only when the screen turns on. This means that only after a device boots up or awaking the phone from a sleeping state will make the screen as bright as the value defined by the System.SCREEN_BRIGHTNESS variable. Consequently, changing only that variable won’t be enough to preview the brightness level as the brightness value need to be set for the window.

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That’s why it’s necessary to access the current window brightness by setting the screenBrightness property located at the LayoutParams object that is obtained from the current window. Then, we use the same value to set the system brightness and window brightness, so it can be previewed before its set.

Let us create simple application to demonstrate how we can change brightness of the system.

Quick Links

• Project Structure
• Code Listings
• Demo
• Download Source Code

Project Structure

Code Listings

Layout XML:

Open layout XML present under /res/layout folder and replace the XML with the below one.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Slide the bar to change the brightness:" />

    <SeekBar
        android:id="@+id/brightbar"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="30dip"
        android:layout_marginRight="30dip" >
    </SeekBar>

</LinearLayout>

Application layout:

AndroidBrightnessActivity.java:

Open AndroidBrightnessActivity and replace the default code with below one. I hope the java code is self explanatory since each line is added with comments.

package com.prgguru.example;

import android.app.Activity;
import android.content.ContentResolver;
import android.os.Bundle;
import android.provider.Settings.SettingNotFoundException;
import android.provider.Settings.System;
import android.util.Log;
import android.view.Window;
import android.view.WindowManager.LayoutParams;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;
import android.widget.TextView;

public class AndroidBrightnessActivity extends Activity {//UI objects//
	//Seek bar object
	private SeekBar brightbar;

	//Variable to store brightness value
	private int brightness;
	//Content resolver used as a handle to the system's settings
	private ContentResolver cResolver;
	//Window object, that will store a reference to the current window
	private Window window;

	TextView txtPerc;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        //Instantiate seekbar object
        brightbar = (SeekBar) findViewById(R.id.brightbar);

        txtPerc = (TextView) findViewById(R.id.txtPercentage);

        //Get the content resolver
        cResolver = getContentResolver();

        //Get the current window
        window = getWindow();

        //Set the seekbar range between 0 and 255
        brightbar.setMax(255);
        //Set the seek bar progress to 1
        brightbar.setKeyProgressIncrement(1);

        try 
        {
        	//Get the current system brightness
        	brightness = System.getInt(cResolver, System.SCREEN_BRIGHTNESS);
		} 
        catch (SettingNotFoundException e) 
		{
        	//Throw an error case it couldn't be retrieved
			Log.e("Error", "Cannot access system brightness");
			e.printStackTrace();
		}

		//Set the progress of the seek bar based on the system's brightness
		brightbar.setProgress(brightness);

		//Register OnSeekBarChangeListener, so it can actually change values
		brightbar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() 
		{
			public void onStopTrackingTouch(SeekBar seekBar) 
			{
				//Set the system brightness using the brightness variable value
				System.putInt(cResolver, System.SCREEN_BRIGHTNESS, brightness);
				//Get the current window attributes
				LayoutParams layoutpars = window.getAttributes();
				//Set the brightness of this window
				layoutpars.screenBrightness = brightness / (float)255;
				//Apply attribute changes to this window
				window.setAttributes(layoutpars);
			}

			public void onStartTrackingTouch(SeekBar seekBar) 
			{
				//Nothing handled here
			}

			public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) 
			{
				//Set the minimal brightness level
				//if seek bar is 20 or any value below
				if(progress<=20)
				{
					//Set the brightness to 20
					brightness=20;
				}
				else //brightness is greater than 20
				{
					//Set brightness variable based on the progress bar 
					brightness = progress;
				}
				//Calculate the brightness percentage
				float perc = (brightness /(float)255)*100;
				//Set the brightness percentage 
				txtPerc.setText((int)perc +" %");
			}
		});	
    }}

Add WRITE_SETTINGS uses-permission in AndroidManifest.xml

<uses-permission android:name="android.permission.WRITE_SETTINGS"></uses-permissi

Demo

Let us test the application:
Run click on the project >> Run as >> Android application
You could see following screens:

Download Source Code

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I hope you enjoyed the post!!
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