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.


-- Using an object as the value container:
on SetMyProp pKey, pVal
   set the uPropSet[pKey] of <someobject> to pVal
end SetMyProp

function GetMyProp pKey
  return the uPropSet[pKey] of <someObject>
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.com                http://www.FourthWorld.com

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