title: Property Notification Changed equivalent in C++/CX bindings
body: <p>In C#, I often created property getters that returned the result of a function call. This meant that I was required to trigger property change notifications manually using OnPropertyChanged. This process is well documented for C# and VB, but I can't seem to find a C++/CX equivalent. Does such a thing exist, or do I have to find a new programming pattern?</p>
  
  <p>Here's a basic example to show my issue:</p>
  
  <pre><code>public:
      property int FooSquared {
          int get() { return _calculateFooSquared(); }
      }
  
  private:
      int _foo;
  
      int _calculateFooSquared() {
          return _foo * _foo;
      }
  
      void _setNewFoo(int newFoo) {
          // When _foo gets updated here, anyone bound to FooSquared
          // needs to be updated. How do I trigger an update?
          _foo = newFoo;
      }
  </code></pre>