[flexcoders] Databinding of a read only property

[durnelln]

Hi all,

How do I make a read-only property bindable for users of my class?  
It sounds so simple but has me stumped at the moment.  I'm sure there 
must be a simple solution but for the life of me I can't figure it 
out...

E.g. say I have a property testProp which is maintained by my class 
and must not be publicly set-able from outside.  I do however want 
outside users to be able to bind to testProp so that they receive 
notifications when it changes.

An example of a read-only bindable property would be 
ArrayCollection.length.  You can bind to this but cannot change it.  
How do I do the same thing with testProp?

I tried...

  protected var _testVar:uint = 10;
  [Bindable]
  public function get testVar():uint
  {
        return _testVar + 1;
  }
  protected function set testVar(value:uint):void
  {
        _testVar = value;
  }

...hoping to hide the setter from the outside world but outside users 
CAN still change testProp with myClassInstance.testProp=10!!

Thanks for your help,

Nick.