17 Feb
2010
17 Feb
'10
9:07 p.m.
Hi Nick,
My understating is the following:
1) For each specific Distribution, PRComponents keep track of the
default attribute values for each Widget (i.e., user preferences for
that Distribution). PRDistribution>>childrenWidget is an example of
such specification.
2) At runtime, when Widgets are instantiated for each Session, these
default values are affected to their respective Widget attribute by
WAComponent >> initializeOwner:link:, itself called by PRComponent >>
componentFor:, in turn called by PRContext >> buildComponent:for:.
PRWidgets overrides #write:using: to keep track of its attribute
values in its properties dictionary (instead of widget specific
accessors). This design decision facilitates the implementation and
maintenance of specific Widgets.
Hoping this helps,
Reza
At 19:56 17/02/2010, Nick Ager wrote:
Hi,
I'm writing this as PRWidget initialisation had me confused for a
while, and I guess it might confuse other newcomers. I'd also like
to check with the list that my understanding is correct.
For example given the code below:
PRDistribution>>childrenWidget
^ childrenWidget ifNil: [childrenWidget := (PRComponent named: 'children')
componentClass: PRChildrenWidget;
write: 2
using: PRChildrenWidget descriptionLevel;
write: true
using: PRChildrenWidget descriptionExpand;
yourself
]
and:
PRChildrenWidget class>>descriptionExpand
^ MABooleanDescription new
default: self defaultExpand;
parameterName: 'expand';
accessor: #expand;
label: 'Expand';
priority: 310;
yourself
I would have expected an accessor "PRChildWidget>>expand:" to be
called with the value: 'true'. I created my PRWidget derived class
based on this assumption. However my equivalent setter was not being
called and a closer look showed PRChildWidget to have no setters
only getters. The getter reads as:
PRChildWidget>>expand
^ self read: #descriptionExpand
What's actually happening is "PRComponent>>description" is being
called, not as I'd imagined: "PRChildWidget>>description".
tracing through the following code:
PRComponent>>write: anObject using: aDescription
(self basicDescription includes: aDescription)
ifTrue: [ super write: anObject using: aDescription ]
ifFalse: [
(anObject notNil and: [ aDescription isDocumentDescription ])
ifTrue: [ anObject owner: self ].
self settings at: aDescription put: anObject ]
reveals the code: "self settings at: aDescription put: anObject" is
called, so "true" is placed in a settings Dictionary keyed by:
#descriptionExpand
I've just about understood the code so far, and though I haven't
traced through PRChildrenWidget instantiation it looks like in
WAComponent>>initializeOwner:link: that the settings are copied to
the newly created PRChildrenWidget object.
Phew.
I think I can see why there's complexity, but seems a shame that it
in WAComponent>>initializeOwner:link: the code couldn't call the
accessors of the componentClass assuming that the Magritte
descriptions were configured to use an accessor pattern.
Or perhaps I've misunderstood??
Cheers
Nick
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