title: Notifying subclass of QAbstractItemModel about changes
body: <p>I've got a question about notifying a model of the changes made to some other object which it stores a reference to.</p>
  
  <p>I'm aware of the signal dataChanged(), but I'm not sure how to use it. For example, my model stores a reference to some other object (let's call it myObjPtr). The model queries myObjPtr for its contents only when the methods rowCount(), columnCount(), data() and others are called on the model.</p>
  
  <p>Then, if I make some changes to the contents of myObjPtr, how should I notify the model so that it could emit the dataChanged() signal with proper arguments? Should I use the model's setData() method? Which arguments should I pass to it if I, for instances, deleted or replaced some elements in myObjPtr?</p>
  
  <p>Thank you.</p>