Ah it makes so much sense now. For those that are not up with the
attribute-event-handler debate, it is a semantic discussion about the
appropriate way to design flexible laszlo components. There are two
dominant patterns:
One: Attributes define state, and things respond to that state
Two: Events define interest, and things respond to that interest by
retrieving and using attributes
I'll refer to them as events and attributes below
The two seem almost interchangable but there is a difference in program
design. The biggest difference is that the attributes model is simpler
to teach and predict. The idea that there is a second event system which
attribute access almost covers leads to confusion. Another is that the
attribute model is simpler to implement in other more powerful languages
(python) where setattr and getattr remove the need for the .setAttribute
syntax altogether; writing LZX to the Attributes spec represents a more
portable codebase. Events are something pulled more from other languages
and less from the lzx model to begin with, so i would argue. When first
learning laszlo I was safely able to forget about the event tag, and
i've been 100% okay without it (but for one pitfall i hacked around
using getTime() to change values every time, which i'm okay with, for now)
The more-recently introduced condition the cautionary note PT wrote
speaks about is that there is a case when attributes will fail to send
events, requiring the use of the event tag, in one edge case. I don't
know if everyone is following, but this is something we can choose, and
it was done for a reason. I'm hoping for a flag in future version to
allow a pure attribute model, as i don't have the event tag in _any_ of
production code! And also, because that characteristic seems like it
would be in a pure LZX implementation (i.e. not javascript but something
more powerful, like python or ruby)
So, i have a question for the list at large, not PT or Henry who do
enough :) For anyone reading this, when was the last time a listmember
reading this used <event> so as to work with handlers, anywhere, in any
code base? Has anyone considered this perhaps, or like me, never thought
of it until it wasn't there?
Kind regards,
j.
P T Withington wrote:
Just to be clear, the idea proposed in
http://jira.openlaszlo.org/jira/browse/LPP-7816
is not yet implemented. Currently, you can only use <handler> to connect to an event
that is already declared (either explicitly using <event> or implicitly on an
attribute).
And one caution: If you create a handler on the implicit event associated with
a constrained attribute, the handler will _only_ be invoked when the attribute
changes value. Consider this example:
<canvas>
<view layout="axis: y; spacing: 5">
<attribute name="set" value="false" />
<attribute name="followset" value="${this.set}" />
<handler name="onset" args="newvalue">
Debug.info("set: %w", newvalue);
</handler>
<handler name="onfollowset" args="newvalue">
Debug.info("followset: %w", newvalue);
</handler>
<button onclick="parent.setAttribute('set', true)">setAttribute('set',
true)</button>
<button onclick="parent.setAttribute('set', new Date())">setAttribute('set', new
Date())</button>
<event name="send"/>
<handler name="send" args="eventvalue">
Debug.info("sent: %w", eventvalue);
</handler>
<button onclick="parent.send.sendEvent(true)">sendEvent(true)</button>
<button onclick="parent.send.sendEvent(new Date())">sendEvent(new
Date())</button>
</view>
</canvas>
Notice that although the handler "onset" is invoked every time you set the attribute, whether the
value changes or not, the hander "onfollowset" is _only_ invoked when the value it is constrained to
changes. Personally, if I want to send events, I prefer to be explicit about it, as shown in the second half
of the example, and declare the <event> and <hander> and use `sendEvent`, rather than relying on
the implicit events sent when attributes change.
On 2009-12-18, at 17:23, cem sonmez wrote:
@P T Withington : I looked at your your solution for creating delegates.
When i need to use the delegates, i m going to use the way that you
mentioned. While looking at the developer documentation of openlaszlo, I
hadnT understand the meaning of delegates and the usage of it. it seemed to
me a bit confused :) Now, i think know more about delegates than before,
thanks
@jamesr : also thank you for the information. I worked out the problem. I
used an attrbiute in the connection.lzx
<attribute name="connectionOK" value="false" type="boolean"/>
and in the case of "NetConnection.Connect.Success", i set it to true.
Then while creating an object of sharedObject, i used like that :
<sharedObjectChat id="soChat">
<handler name="onconnectionOK" reference="conn">
Debug.info("connectionOK attribute operation, value
:%w",conn.connectionOK);
if (conn.connectionOK==true) {
//this.setAttribute("createSharedObject",true);
this.connect("chat", conn._conn, true);
this.so.client=this;
}
</handler>
</sharedObjectChat>
So itS ok now. İt is impossible to learn something wihout making mistakes :)
Best regards.
2009/12/18 P T Withington <[email protected]>
I have a proposed "solution" for the LZX programmer having to create
delegates in script in:
http://jira.openlaszlo.org/jira/browse/LPP-7816
Basically, I want you to be able to declare a handler without attaching it
to an event at declaration time (and you would later use script to register
the handler on the event it is to handle). The main purpose for this change
is that <handler /> will automatically be managed, whereas delegates must be
manually managed (and destroyed) or they can lead to memory leaks.
On 2009-12-18, at 16:03, jamesr wrote:
for the record, the two use cases for making a delegate are
1) you want to compute what object to latch onto programmatically and
2) you want to latch onto something that is not yet created at the
handler init phase.
don't see any other use, although the two above are obviously important
cem sonmez wrote:
you are exactly right. I want to make some operations when the
netconnection successful event is fired. Actually i m trying to get the
shared object on the server side, so at first i need a netconnection
instance to do that. ThatS why i thought that i should try delegates. I
havenT used delegates before, but i thought that this is the just one
solution to handle the operations depend on the related event.
The method you said, using an attribute in the connection class seems
the better way. Till now, i havenT needed the delegates. I hope using
connection status attribute in the connection class will fix the problem.
I m going to post back the results here of course.
Thanks for the reply J
2009/12/18 jamesr <[email protected] <mailto:[email protected]
I can tackle it. let's see; i'd write the following, after an
introduction (all code is untested and represents a pattern, adapt
it as you will)
Your problem: You want to do is send a "connection successful"
event that you can catch, signaling that a method is to be called
to continue using the connection. You seem to be trying to do it
by setting up the delegate manually, when i think, looking at your
code, that you have hooks to fire events on laszlo nodes that can
communicate this state change.
Solution: An event is anytime you use x.setAttribute() by the way
- that's what it does, makes sure that handlers are fired. That
said, if you declare an attribute of any laszlo node and in your
code, when you have success on your net connection, you say
"somenode.setAttribute('success, true);" then in another node you
can say, <handler name="onfoo" reference="somenode">...</handler>
and in that code you can then do what ever other steps are
required to use the connection.
Further thought if i'm wrong: can you say why it is you decided to
use manual delegates? it might make things clearer for me, i've
not used the net connection code you have there but make guesses.
.j.
cem sonmez wrote:
doesnT anyone have any idea. I got stuck here. Waiting for
someones advices.
Thanks
2009/12/18 cem sonmez <[email protected]
<mailto:[email protected]> <mailto:[email protected]
<mailto:[email protected]>>>
hi
when i try do use the delegate such like :
if( typeof this.del == "undefined" ) {
this.del = new LzDelegate(this, "connect('chat',
conn,
true)" );
} this.del.register(conn,
"netStatusHandler('NetConnection.Connect.Success')" );
}
I m getting the error on the debug like :
*soChat.connect('chat', conn, true) => (void 0) (must be a
function)*
Actually i want to do this : call the *connect* method on the
class when the netStatusHandler method of the *conn* object
has
been completed. I m not sure that am i using the delegate
correctly (as i m getting the error, of course not :)).
I have attached the relevant files.
Can anyone help me what i m missing to do.
Kind regards.
-- Cem SONMEZ
-- Cem SONMEZ
--
Cem SONMEZ
--
Cem SONMEZ
