[Adobe-source-devel] View concept singleton state

[Foster T. B. <fbr...@ad...>]

Hey all,

I wanted to email the group regarding something I'm implementing for =20
the preset widget, because I think it can be lifted into the View =20
Concept as a whole.

A while back Mat and I were talking about the following problem: what =20=

is the proper behavior of a view when it is asked to display a value =20
it cannot display? As an example, let us say I have an 'analog clock' =20=

display and it is asked to show the time 25:75. What should the clock =20=

do? To solve this, (thus far) we came up with the idea that every =20
view should have a singleton state. The singleton state for a view is =20=

entirely implementation-specific; for instance in the clock example, =20
the view could set itself to noon and make the clock have a red =20
background -- something obvious to the user that says "I no longer =20
accurately reflect the value in the model I have been asked to =20
display". The instant the model communicates to the view a new value =20
that it can display, the view should display the new value normally.

The notion of a 'singleton value' does not exist, so the ability for =20
the user to put a widget into the singleton state is prohibited. What =20=

would trigger the singleton value for a view usually takes the form =20
of controller 'A' setting the value of a cell that view 'B' (also =20
bound to the cell) cannot display. The value would be valid for A as =20
a controller but not B as a view, so B reverts to the singleton state.

Therefore, in the case when the view is also a controller (aka a =20
widget), there is an additional requirement to be placed on the =20
widget while in the singleton state. In addition to the above view =20
requirement, the widget must also allow for valid user manipulation =20
of the controller while displaying the singleton state. In the clock =20
example above, (should the clock view be part of a clock widget), the =20=

singleton state should allow for the user to set another (valid) time =20=

(for example, by dragging the hands of the clock with the mouse).

As a more concrete example, I am reworking the ASL preset widget so =20
it models the View concept -- it is bound to a 'result' cell of the =20
property model. When the result cell is updated, the preset widget =20
compares its list of available presets against the result cell -- =20
when a preset is found whose contents are a subset of the result =20
cell, that preset is selected. The singleton state, then, occurs when =20=

the result cell is in a state for which no preset exists. The display =20=

behavior I am implementing is to append a menu item named "Custom" to =20=

the preset category list. This will still let the user select a new =20
preset category from the preset category list, but at the same time =20
clearly tells the user "the dialog as it stands matches no presets."

Thoughts?

Blessings,
Foster


--
Foster T. Brereton              <=E1=BC=B0=CF=87=CE=B8=CF=8D=CF=82><     =
         Romans =20
3:21-26
A d o b e   S o f t w a r e   T e c h n o l o g y   L a b
"What 99 percent of programmers need to know is not how to build =20
components but how to use them." -- Alexander Stepanov
"Now we have very simple code and the meaning is perfectly clear. =20
Drink the Kool-Aid" -- Sean Parent