title: turn on/off hardware key backlight
body: <p>Before i ask this question, i've realized it, but it is based on some conditions.</p>
  
  <p>Try1: Change the chmod of file '/sys/class/leds/button-backlight/brightness' to 777, the original file is readable but not writeable, then write '1' to this file to turn on led backlight, '0' to turn off. However, i don't want to change the property of this file.</p>
  
  <p>Try2: something like 'Try 1', that is: <code>Runtime.getRuntime().exec("echo 0 &gt; /sys/class/leds/button-backlight/brightness");</code> to turn off, <code>Runtime.getRuntime().exec("echo 1 &gt; /sys/class/leds/button-backlight/brightness");</code> to turn on, but this requires your phone has been rooted or you're a super user when execute the code. So, it isn't the solution that i want.</p>
  
  <p>My thought: i can follow the way that Android System itself turn on/off the led backlight when we touch key like 'Menu', 'Home', 'Back'. But, i don't know how to track or find the ralated code in Android Open Source Code.</p>
  
  <p>I do really appreciate any tip, any thought or any possible way that you provide.</p>