title: Is There A Lost Focus Window Event in Objective C?
body: <p>Coming from a .NET background I'm used to events getting fired so trapping a lost focus event is easy but I'm not sure how to do this in Obj-C.  Basically I want my app to know when another application has gotten focus and it no longer has it so it can perform some actions.</p>
  
  <p>Can you please tell me how I can implement this kind of functionality in Obj-C for an OSX app?</p>