title: Low memory warning for NSObject
body: <p>I have a subclass of NSObject, it is a singleton which loads a list of images into memory, either from hard drive or downloads them from the internet.</p>
  
  <p>I want to release the images stored in memory if the app recieves a low memory message, like in a UIViewController. (it then gets the images from hard drive when it next needs them).</p>