David Epstein wrote:
> Control “A” has many custom properties that are set by a variety
> of other controls. If Control “A” has a "setProp property1”
> handler, it can react when property1 gets set. But is there a
> way to give Control “A” a general handler that will be triggered
> whenever any of its custom properties is set?
I don't know of a way to trap getProp and setProp generically, and that
may not be bad since it would affect the performance of all custom
property access, whether it's the subset of properties you're interested
in or not.
An alternative could be to put the properties you want custom handling
for into a custom property set of their own, e.g.:
getPRop uPropSet[pKey]
put the params
end uPropSet
on mouseUp
get the uPropSet["key1"] of me
end mouseUp
...puts this in the Message Box:
uPropSet "key1"
This will allow open-ended trapping of property keys, but limited in
scope to the set you need that for.
A word of caution with dependency on getProp and setProp:
Those messages are subject to suspension during lockMessages, which may
be exactly what you want, or may have unintended side effects that can
be maddening to track down if you don't keep that in mind.
Using getProp and setProp requires review of your code base, including
any third-party libraries, which may lock messages so you can evaluate
the implications for your circumstance.
If you need consistently reliable ways to trigger custom evaluation
consider accessor handlers instead. LockMessages only prevents system
messages; calling a custom handler is not affected by lockMessages.
Examples:
-- Using an object as the value container:
on SetMyProp pKey, pVal
set the uPropSet[pKey] of to pVal
end SetMyProp
function GetMyProp pKey
return the uPropSet[pKey] of
end GetMyProp
-- Using an array variable as the value container:
on SetMyProp pKey, pVal
put pVal into sPropVarA[pKey]
end SetMyProp
function GetMyProp pKey
return sPropVarA[pKey]
end GetMyProp
-- Usage for either storage method:
on mouseUp
SetMyProp "key1", "val1"
end mouseUp
on mouseUp
put GetMyProp("key1") into fld 1
end mouseUp
Fun: If you abstract data access using normal custom handlers, you have
one-stop-shopping to change the storage mechanism. If you don't need
persistence across sessions a variable may do, and if you need
persistence you can store in an object whose stackfile gets saved, or
encode the array variable and save that to disk, or use a local
database, or even use any form of remote storage across the internet if
you like -- all by updating just two handlers.
--
Richard Gaskin
Fourth World Systems
Software Design and Development for the Desktop, Mobile, and the Web
ambassa...@fourthworld.comhttp://www.FourthWorld.com
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