MVC problem - infinite loop?

Question

I'm going to use a horribly oversimplified example to make my point here, because if I were to describe the actual code I'm looking at, it would take the better part of the afternoon and I'd probably bore you all to tears in the process. So, for the sake of argument, let's assume the following model object:
public class MyModelObject
  private int a;
  private int b;
  private int c;
  public void setA(int newA)
    a = newA;
    b = newA + SOME_CONSTANT;
    c = newA + SOME_OTHER_CONSTANT;
  public void setB(int newB)
    this.setA(SOME_CONSTANT-newB);
  public void setC(int newC)
    this.setA(SOME_OTHER_CONSTANT-newC);
  public int getA()
    return a;
  public int getB()
    return b;
  public int getC()
    return c;
}So what we see from this is that the setter for one class property actually changes the value of all three class properties (whether this is good design or not is questionable, but keep in mind this is a horribly simplified example for discussion purposes). The point is that the rules regarding the internal state of MyModelObject are governed entirely within that class - the controller and view don't know about these rules (again, questionable design, but bear with me here).
Now let's imagine we have a view class that displays a MyModelObject instance and allows the user to change the value of a, b, or c. We also have a controller class that observes the view and responds to changes. When the user modifies the value of, let's say b, the controller will respond to that change by calling the setB() method in MyModelObject. Problem is, now the model and the view are out of synch... someone has to tell the view that the other two class properties have also been modified as a result of calling setB() - whose responsibility is this? Should the model inform the view that something has changed so that the view can redisplay it, or should the view observe the model and automatically redisplay whenever the model is modified?
More importantly - let's say the controller is observing the view for changes, and the view is observing the model for changes... how do you avoid an infinite loop? For example, the user changes the value of b in the view, which causes the internal state of MyModelObject to be modified, which causes a change in the view, which causes a change in the model, and so on and so forth.
A twist on the above problem is that it is illegal in some Swing components (JTextPane, for instance) to modify the view while a change notification is in progress... so something like this would throw an IllegalStateException:
//somewhere in the controller
public void insertUpdate(DocumentEvent docEvent)
  //update the model
  myModelObject.handleChange(docEvent);
  //now redisplay since the model has changed:
  myTextPane.display(myModelObject);
  // IllegalStateException is raised - Attempt to mutate in notification
}This fails because you can't change the state of the view component in the event handler for a view change event. How do you get around this using proper MVC architecture? Or am I completely out to lunch here?

Answer 1

The view shouldn't send events to the controller unless they make sense... For example, it shouldn't fire a change event when the user types in a new value. But only if the user presses enter, or the view loses focus (if this gesture is taken as equivalent).
So when the change of the view comes from the side-effects of a setter of some property, it should fire no event (so that it will not loop). So it sounds no big problem (if such a distinction of events is easy - it should).