We're discussing the case where a component distributes its model to its
children or behaviors.
For the component developer it's easier to assume that the model can't
be changed without its consensus (i.e. by offering a generic #setModel()).
Of course this can be handled perfectly by a coding guideline. I always
tell people to *never* change a component's model.
I cannot count times where I'm called to a developer's IDE with him
having absolutely no clue why something entered here doesn't display
over there: In many cases this is caused by setting models.
But a protected #setDefaultModelObject() would make this explicit in the
API.
Sven
On 09/27/2012 07:09 PM, Igor Vaynberg wrote:
i thought the issue we were discussing here is the way the models are
linked...which is not solved by making setdefaultmodelobject
non-public.
-igor
On Thu, Sep 27, 2012 at 10:04 AM, Sven Meier <s...@meiers.net> wrote:
If you extend GenericPanel you inherit setModel() and getModel(), that's the
whole purpose of this base class.
You want these two methods, otherwise you wouldn't extend it - there's
nothing to fix.
Component#setDefaultModel() is dangerous because it allows others to tinker
with your component innards.
I still think limiting access to #setDefaultModel() is a good idea, but this
is no crucial issue anyway.
Sven
On 09/27/2012 06:16 PM, Michael Mosmann wrote:
Am 27.09.2012 17:51, schrieb Igor Vaynberg:
good point..
-1 from me.. thought it was a good idea, but wasn’t
Michael
so what happens if panel A extends GenericPanel which has setModel?
you havent fixed anything.
-igor
On Thu, Sep 27, 2012 at 8:50 AM, Michael Mosmann <mich...@mosmann.de>
wrote:
Am 27.09.2012 17:32, schrieb Igor Vaynberg:
Hi,
.. i would leave setModel as it is, only make this change for
Component.setDefaultModel().
Michael
-1 on changing setDefaultModel().
1) if B panel's model is truly dependent on A's then that dependency
should be expressed:
add(new BPanel("b", new PropertyModel(this, "defaultModel"));
or do not use the default model slot of B to store the model. that way
setDefaultModel() calls on B will be a noop and you can choose not to
provide a setter.
2) you are only "solving" this for a subset of usecases where the
container (A) is not generic. are we also going to make setModel(T)
protected? that would require the model assignment be done through the
constructor only and would eliminate any possibility of writing
builder-style code. consider a simple example:
new DropDownChoice("foo").setModel(bar).setChoices(baz)...
this kind of code should be possible whether written directly by the
developer in the page or produced by some builder.
-igor
On Thu, Sep 27, 2012 at 5:19 AM, Sven Meier <s...@meiers.net> wrote:
Even a simpler example might fail (no PropertyModel involved):
class APanel extends Panel {
APanel(String id, IModel<Some> model) {
super(id,model);
add(new BPanel("b", model);
}
}
A client using APanel might later change the model, leaving BPanel
working
on the old model:
aPanel.setDefaultModel(otherModel);
You could argue that APanel should be made failsafe when passing the
model:
add(new BPanel("b", new PropertyModel(this, "defaultModel")));
But it would be much easier if APanel could assume that its model
isn't
changed unattendedly.
IMHO changing a component's model isn't the "wicket way" so I'd
suggest
changing the visibility of Component#setDefaultModel() to protected.
Sven
On 09/27/2012 10:47 AM, Martin Grigorov wrote:
I see. This is an advanced way to create a static model :-)
But again I find PropertyModel as the real problem here.
I'll let others give their opinions too.
On Thu, Sep 27, 2012 at 11:39 AM, Michael Mosmann
<mich...@mosmann.de>
wrote:
Am 27.09.2012 09:51, schrieb Martin Grigorov:
Hi,
a dont care about the type issue here.. Maybe i can explain it again
in
an
other way:
APanel uses model instance A and the label uses a property model
instance
P
which uses a reference to model instance A.
After calling APanel.setDefaultModel(B) APanel uses model instance
B,but
label uses model instance P which uses model instance A as before.
So
the
label does not see any changes, because no one tells the model
instance
P,
that it should use B instead of A. I think, there are rare cases for
such
a
usage.
thanks
Michael
Hi,
In this particular code I think the "problem" is PropertyModel,
since
it brings the type unsafety.
Another solution is to make Component<T>, this way we can remove
#setDefaultModel() and have #setModel(IModel<T>) only and such
problems will go away.
But as discussed in early Wicket 1.4 days this will lead to more
typing. With Java 7 diamonds it is half the typing though.
For now you can use GenericPanel, GenericPage and all
FormComponent.
On Thu, Sep 27, 2012 at 10:41 AM, Michael Mosmann
<mich...@mosmann.de>
wrote:
Am 27.09.2012 09:01, schrieb Martin Grigorov:
Hi,
I think, there is a little difference in using setDefaultModel and
setDefaultModelObject .. the first one sets a new model instance,
the
second
only change the value in the existing model. Some pseudo-code:
class APanel extends Panel {
APanel(String id,IModel<Some> model) {
super(id,model);
add(new Label("name",new
PropertyModel(getDefaultModel(),"name"));
}
}
If you replace the value in model, everything is fine and works as
expected.
If you call setDefaultModel you might think, that everything is
fine,
but
its not. A child component does not use
getParent().getDefaultModel()
to
get
these changes. I saw a lot of code like this, which leads to
trouble,
if
you
change the model and not the value.
If there is no benefit in using setDefaultModel over
setDefaultModelObject i
would like to remove this method. This could prevent many "you
might
not
got
the full picture how to use wicket the right way" errors.
Michael
Hi,
Most of the time it is recommended to use a dynamic model, so
there
is
no reason to replace the component's model.
Component#setDefaultModel() gives you semi-dynamic nature - you
can
replace the model completely with a new one. Same with
#setDefaultModelObject().
What is the problem you face with it ?
On Thu, Sep 27, 2012 at 9:57 AM, Michael Mosmann
<mich...@mosmann.de>
wrote:
Hi,
is there any usefull application of
Component.setDefaultModel(...)?
IMHO
this Method is the cause for much trouble without any benefit.
But
maybe
i
did not understand when someone should replace a component
model...
thanks
Michael
