title: iOS touch event triggering by movement of other view
body: <p>Here's the scenario I am trying to implement:</p>
  
  <p>I already have a view that can let user draw doodles by touching inside the view directly (like a doodle canvas). This view implements <code>touchesBegan</code>, <code>touchMoved</code>, and <code>touchEnded</code> handlers to draw lines from touch event parameters.</p>
  
  <p>Now instead of that, I want user to be able to drag and move another UIView on this canvas view and can still draw lines just like they touch directly. For example, user can drag a pen image view on the canvas view to draw pen-style lines.</p>
  
  <p>In this case, how can I transfer the movement of this pen image view to the canvas so it recognize it? One more question: if I want this canvas view to only recognize movements of drag other views rather than touching directly, what I should do?</p>
  
  <p>(Sorry that this question is little too general, just want to get some pointer of it)... Thanks!</p>