Question

I’m trying to create an application always active (ie never goes in the background), with a button that when is pressed reduces the screen brightness. I state that I’m no expert in programming in Android.

Answer 1

You can set screen BRIGHTNESS o button click as:

FIRST WAY:

@Override
  public void onClick(View arg0) {
   // TODO Auto-generated method stub
   int curBrightnessValue=android.provider.Settings.System.getInt(
       getContentResolver(),android.provider.Settings.System.SCREEN_BRIGHTNESS);
   setBrightness(curBrightnessValue-25);//set BRIGHTNESS
  }
private void setBrightness(int brightness) {  
    try {  
      IHardwareService hardware = IHardwareService.Stub.asInterface(  
      ServiceManager.getService("hardware"));  
      if (hardware != null) {  
        hardware.setScreenBacklight(brightness);  
      }  
    } catch (RemoteException doe) {            
    } 

Manifest.xml

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

SECOND WAY:

@Override
   public void onClick(View arg0) {
   // TODO Auto-generated method stub
   int curBrightnessValue=android.provider.Settings.System.getInt(
   getContentResolver(),android.provider.Settings.System.SCREEN_BRIGHTNESS);
   int SysBackLightValue = curBrightnessValue-25;
   android.provider.Settings.System.putInt(getContentResolver(),
   android.provider.Settings.System.SCREEN_BRIGHTNESS,
   SysBackLightValue);
  }

AndroidManifest.xml:

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

and finally for other way to set brightness see this post