How to define a property for getter and Seter settings can be bound _flex

Define private variable for maxfontsize.
public var _maxfontsize:number = 15;
Define Public Getter Method, mark the property
As usable for the source of data binding,
and specify the name of the binding event.
[Bindable ("maxfontsizechanged")]
Public function Get Maxfontsize (): number {
return _maxfontsize;
}
Define public setter method.
Public function set Maxfontsize (value:number): void {
if (value <= 30) {
_maxfontsize = value;
else _maxfontsize = 30;
Dispatch the event to trigger data binding.
Dispatchevent (New Event ("maxfontsizechanged"));
}