[squeakland] What are the differences between a Holder and a Playfield?

Scott Wallace scott.wallace at squeakland.org
Tue Dec 8 00:14:48 EST 2009

On Dec 7, 2009, at 6:57 PM, Steve Thomas wrote:

> Here are the functional differences I have found so far:
> 	• A holder automatically orders things for you visually
> 	• A holder will "resize" to fit its contents (once something is put in)
> What other differences are there?
> Venn Diagram please . . .

A "Holder" is simply a "Playfield" which has had some of its "playfield options" set a particular way that has been found suitable for a number of purposes, particularly for classic "holder-based animations".

The three playfield-option settings that distinguish what we commonly call a Holder are:

  "auto-line-layout" is set to true  (so that elements don't overlap)
  "indicate cursor" is set to true  (so that the "selected" element is shown with a black border)
  "resize to fit" is set to true

So any "playfield" can be made to behave entirely, or partially, like a "holder", simply by adjusting its playfield options; the Holder in the Supplies flap is offered only as a convenience -- it's simply a plain Playfield with the three options set.

(For example, try this:  Get a "Playfield" from Supplies.  From its halo menu get the "playfield options" submenu, and "pin" it up.  Now click the "behave like a holder" checkbox, and notice which three other options get changed.)  

> They both have collection and playfield, um what's the right term(s)?
> 	• Categories? 
> 	• Behaviors and Attributes?
> 	• Predicates and Objects?
> 	• Nouns and Verbs?
> 	• Heeelllllppppp? (no definitely no, help, that's why we are writing the manual ;)
> Stephen

AFAIK "viewer category" is the term in common use.

Holders and Playfields have identical viewer categories, with identical items in them, because (to repeat...) a Holder *is* nothing more than a Playfield with a few options set a particular way.

  -- Scott

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