Re: Updating Multiple Views

On Feb 9, 6:23 pm, "Daniel Pitts" <googlegrou...@xxxxxxxxxxxxx> wrote:
On Feb 9, 12:41 pm, "Jason Cavett" <jason.cav...@xxxxxxxxx> 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.

.