Question

I’m attempting to change the screen brightness from withing a service, like so:

android.provider.Settings.System.putInt(getContentResolver(),
android.provider.Settings.System.SCREEN_BRIGHTNESS, bright);

Problem is that is doesn’t work. Well, actually it succeeds in changing the brightness setting, but the screen brightness doesn’t actually change till I go into the phones settings, look at the new value and hit Ok.

Is there something I have to do after setting the value to get the brightness to change?

Answer 1

I’ve had the same problem of changing screen brightness from within a service, and a couple days ago i have successfully solved it(and updated my app Phone Schedule with brightness feature 😉 ).
Ok, so this is the code you put into your service:

// This is important. In the next line 'brightness' 
// should be a float number between 0.0 and 1.0
int brightnessInt = (int)(brightness*255);

//Check that the brightness is not 0, which would effectively 
//switch off the screen, and we don't want that:
if(brightnessInt<1) {brightnessInt=1;}

// Set systemwide brightness setting. 
Settings.System.putInt(getContentResolver(),
Settings.System.SCREEN_BRIGHTNESS_MODE, Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);
Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS, brightnessInt);

// Apply brightness by creating a dummy activity
Intent intent = new Intent(getBaseContext(), DummyBrightnessActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.putExtra("brightness value", brightness); 
getApplication().startActivity(intent);

Please Note that in the above code snippet I’m using two variables for brightness. One is brightness, which is a float number between 0.0 and 1.0, the other one is brightnessInt, which is an integer between 0 and 255. The reason for this is that Settings.System requires an integer to store system wide brightness value, while the lp.screenBrightness which you will see in the next code snippet requires a float. Don’t ask me why not use the same value, this is just the way it is in Android SDK, so we’re just going to have to live with it.

This is the code for DummyBrightnessActivity:

public class DummyBrightnessActivity extends Activity{

    private static final int DELAYED_MESSAGE = 1;

    private Handler handler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);            
        handler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                if(msg.what == DELAYED_MESSAGE) {
                    DummyBrightnessActivity.this.finish();
                }
                super.handleMessage(msg);
            }
        };
        Intent brightnessIntent = this.getIntent();
        float brightness = brightnessIntent.getFloatExtra("brightness value", 0);
        WindowManager.LayoutParams lp = getWindow().getAttributes();
        lp.screenBrightness = brightness;
        getWindow().setAttributes(lp);

        Message message = handler.obtainMessage(DELAYED_MESSAGE);
        //this next line is very important, you need to finish your activity with slight delay
        handler.sendMessageDelayed(message,1000); 
    }

}

This is how you add your activity to the AndroidManifest.xml, probably the most important part:

<activity android:name="com.antonc.phone_schedule.DummyBrightnessActivity"
            android:taskAffinity="com.antonc.phone_schedule.Dummy"
            android:excludeFromRecents="true"
            android:theme="@style/EmptyActivity"></activity>

A little explanation about what’s what.

android:taskAffinity must be different, than your package name! It makes DummyBrightnessActivity be started not in your main stack of activities, but in a separate, which means that when DummyBrightnessActivity is closed, you won’t see the next activity, whatever that may be. Until i included this line, closing DummyBrightnessActivity would bring up my main activity.

android:excludeFromRecents="true" makes this activity not available in the list of recently launched apps, which you definetely want.

android:theme="@style/EmptyActivity" defines the way DummyBrightnessActivity looks like to the user, and this is where you make it invisible. This is how you define this style in the styles.xml file:

<style name="EmptyActivity" parent="android:Theme.Dialog">
    <item name="android:windowIsTranslucent">true</item>
    <item name="android:windowAnimationStyle">@android:style/Animation.Toast</item>
    <item name="android:background">#00000000</item>
    <item name="android:windowBackground">#00000000</item>
    <item name="android:windowNoTitle">true</item>
    <item name="android:colorForeground">#000</item>
</style>

This way your DummyBrightnessActivity will be invisible to the user. I’m not shure if all of those style parameters are really necessary, but it works for me this way.

I hope that explains it, but if you have any questions, just let me know.