title: Set lock screen background in Android (like Spotify do)
body: <p>I know that this topic has been already discussed <a href="https://stackoverflow.com/questions/8071162/android-set-lock-screen-wallpaper-programmatically" title="here">here</a>, <a href="https://stackoverflow.com/questions/2653954/how-to-set-android-lock-screen-image" title="here">here</a> and <a href="https://stackoverflow.com/questions/14728824/how-to-change-the-lockscreen-wallpaper-in-android" title="here">here</a>, and the answer seems to be that it is not possible. </p>
  
  <p>But I recently installed Spotify in my Nexus 4 (4.4.2), and it seems to be possible. When I listen a song in Spotify the lock screen background change with the cover of the album that I'm listening (see screenshots). </p>
  
  <p>My theory was: 
  when the phone is locked they <a href="https://stackoverflow.com/questions/10160267/how-to-set-image-as-wallpaper-programmatically">change the phone wallpaper</a> with the album cover in order to change also the lock screen background, then they set back the previous one when the phone is unlocked. But this is not how they do it, because in the permissions list of Spotify there is no "android.permission.SET_WALLPAPER"... :( </p>
  
  <p>How do they do it? Some theory? </p>
  
  <p><img src="https://i.stack.imgur.com/CBptw.jpg" alt="Screenshot lock screen">
  <img src="https://i.stack.imgur.com/m2yLj.png" alt="Screenshot lock screen"></p>