In the default event system, what you get if you don't write a custom
setter, sends an event every time you call setAttribute. It does
_not_ make any optimization to not send events if you happen to set an
attribute to a value it already has.
A side note for the interested reader:
It's possible to turn on manually this optimization if you pass as the
third argument to "setAttribute()" ?true?, e.g.
foo.setAttribute("text", "hello world!", true)
(That way the setter is not called when the value did not change.)
If you poke around Jira, you will see many
bugs of the form "setting foo does not send the onFoo event".
Invariably, these are from broken custom setters where the setter
writer forgot about the event part of the setter's contract.
LZX-level changes won't help for LFC bugs (LPP-2273) ;-)
1) If you write a setter in the open tag of an attribute, the event is
always sent (you don't get to control the sending of the event).
E.g., if I say:
<attribute name="foo" setter="this._fooState = foo" />
the compiler will automatically append `this.sendEvent('onfoo', foo)`
to the setter body. (How many places in your code have you written
these shorthand setters and actually remembered that you need to send
an event too?)
2) If you _must_ get control over the sending of the event, you have
to ask for it, and use the long-hand <setter> tag. E.g.:
<setter name="foo" args="newFoo" event="false">
...
if (<i really want to send the event>) this.sendEvent('onfoo',
newFoo);
</setter>
When do you send the event?
1. after setting the property
a) requires code analysis
b) likely to be more natural
c) property may be have any name -> problem...
2. at the end of the setter
a) what happens if the user places return statement in the setter? [1]
b) or an error was thrown?
When do you send no event?
1. if you override a setter
a) because the super-setter should handle this,
b) but if the super-setter is not called? (by purpose or unintentionally?)
[1] leads to an often encountered code structure in OL sourecode (hey,
there is a thing called "else"!):
//start of method
....
if (condition) {
.....
*return;*
}
.....
//end of method
