Binding to a read-only getter in AS3

Question

Consider the following code:

[Bindable(event="ReportHeaderVO_effectiveFromDateJulian_updated")]
public function set effectiveFromDateJulian ( value:Number ) : void
{
    _effectiveFromDateJulian = value;
    dispatchEvent( new FlexEvent("ReportHeaderVO_effectiveFromDateJulian_updated") );
}

public function get effectiveFromDateJulian () : Number
{
    return _effectiveFromDateJulian;
}

public function get effectiveFromDate () : Date
{
    return DateUtil.convertJDEJulianToDate(_effectiveFromDateJulian);
}

There is a setter and a getter for the effectiveFromDateJulian which is a number representation of the date. I have provided a seperate getter which retrieves the same value, only converted to a proper date. It is a getter only though and relies on the setter for the numeric property to get its data from; so the effectiveFromDate property is effectively read-only.

Data binding works on the effectiveFromDateJulian property; any updates work fine and notify everything properly. But when binding to the effectiveFromDate (getter only) property, I get a warning from the compiler:

warning: unable to bind to property 'effectiveToDate' on class 'com.vo::ReportHeaderVO'

Is there a way to make it possible to bind to this read-only property? I would assume I would have to dispatch an event on the setter that effects the read-only property, but I don't know what that would look like.

This is a simple example, you could imagine a read-only property that depends on several setters to function and when any of those setters are updated the read-only property would need to fire a propertyChanged event as well. Any ideas? Please let me know if I need to clarify anything.

Update: From the Adobe documentation here:

http://livedocs.adobe.com/flex/3/html/help.html?content=databinding_8.html

Using read-only properties as the source for data binding

You can automatically use a read-only property defined by a getter method, which means no setter method, as the source for a data-binding expression. Flex performs the data binding once when the application starts.

Because the data binding from a read-only property occurs only once at application start up, you omit the [Bindable] metadata tag for the read-only property.

And this makes sense for constant values, but in this case the value does change, it just doesn't get set directly.

Answer 1

Make the readonly getter Bindable and dispatch the corresponding event from the original setter method.

[Bindable(event="ReportHeaderVO_effectiveFromDateJulian_updated")]
public function set effectiveFromDateJulian ( value:Number ) : void
{
    _effectiveFromDateJulian = value;
    dispatchEvent( new FlexEvent("ReportHeaderVO_effectiveFromDateJulian_updated") );
    dispatchEvent( new FlexEvent("ReportHeaderVO_effectiveFromDate_updated") );
}
[Bindable(event="ReportHeaderVO_effectiveFromDate_updated")]
public function get effectiveFromDate (date:Date) : Date
{
    return DateUtil.convertJDEJulianToDate(_effectiveFromDateJulian);
}