setProp and Lock messages

Richard Gaskin ambassador at fourthworld.com
Sun Dec 4 14:10:51 CST 2011


Pete wrote:

> I think the reference to the documentation not being believable alluded to
> the LC documentation not the datagrid documentation.  The LC Reference
> Manual and the dictionary are old and definitely contain inaccuracies.  On
> the topic of setprop and recursion, for example, the reference manual
> clearly states that you don't need to user lock messages to prevent
> recursion but, as several people have mentioned in this thread, you do.

Here's what the docs say with regard to recursion for setProp:

    Caution! If a setProp handler in one object's script sets the
    custom property for a different object, and the first object
    is in the second object's message path, a runaway recursion
    will result. For example, if the following handler is in a
    card script, and you set the "myCustomProperty" of a button
    on the card, runaway recursion will result:

     setProp myCustomProperty newValue
       set the myCustomProperty of the target to newValue + 1
       -- Because the target is the button, and this handler is in
       -- the card, the above statement sends another setProp trigger
       -- to the button.
     end myCustomProperty

    To avoid this problem, set the lockMessages property to true
    before setting the custom property.


I believe that's correct, and have not experienced any bugs which differ 
from that description.

Has anyone here found a recipe for a behavior which contradicts that 
description?

--
  Richard Gaskin
  Fourth World
  LiveCode training and consulting: http://www.fourthworld.com
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