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From "nigel magnay (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLEX-27837) ChangeWatcher bug
Date Mon, 23 Sep 2013 08:47:13 GMT

    [ https://issues.apache.org/jira/browse/FLEX-27837?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13774385#comment-13774385
] 

nigel magnay commented on FLEX-27837:
-------------------------------------

>But AFAICT, the code is correct. The weakReference parameter is not passed into the ChangeWatcher
>constructor, but is assigned to the instance after construction and before reset() is
called where it appears >to be properly applied.
>

That is true for the first change watcher in the chain, but NOT for the subsequent ones. It
has nothing to do with the next reference, it's the reference back to 'handler' that's at
issue.

The line here:
 var w:ChangeWatcher =
                new ChangeWatcher(chain[0], handler, commitOnly,
                    watch(null, chain.slice(1), handler, commitOnly)); 

Is a recursive call. The parameter for the recursive call is being defaulted, so it's equivalent
to
 var w:ChangeWatcher =
                new ChangeWatcher(chain[0], handler, commitOnly,
                    watch(null, chain.slice(1), handler, commitOnly, >>> false <<<
)); 

So if we call with something like
  ChangeWatcher.watch(thing, ["a","b","c"], handler, false, true);

Trying to follow the API, which states:

   @param useWeakReference (default = false) Determines whether
   the reference to <code>handler</code> is strong or weak. A strong
   reference (the default) prevents <code>handler</code> from being
   garbage-collected. A weak reference does not.

Then this is easily demonstrated to not be true. The ChangeWatcher created for monitoring
'b's value of 'c' has a useWeakReference value set to FALSE in the recursive call.


                
> ChangeWatcher bug
> -----------------
>
>                 Key: FLEX-27837
>                 URL: https://issues.apache.org/jira/browse/FLEX-27837
>             Project: Apache Flex
>          Issue Type: Bug
>          Components: .Unspecified - Framework
>    Affects Versions: Adobe Flex SDK Previous
>         Environment: Affected OS(s): Windows
> Affected OS(s): Windows XP
> Language Found: English
>            Reporter: Adobe JIRA
>              Labels: easyfix
>
> When I used this class BindingUtils to binding work, I called this method:
> public static function bindSetter(setter:Function, host:Object,
>                                       chain:Object,
>                                       commitOnly:Boolean = false,
>                                       useWeakReference:Boolean = false):ChangeWatcher
> I found there is a wrong description about the "useWeakReference", below is the signature
of useWeakReference in the API Document:
> 	useWeakReference : Boolean
> (default = false) Determines whether the reference to the host is strong or weak.
> but I don't think it determines the host, but the ChangeWatcher instance itself, it determines
whether the reference to the ChangeWatcher instance is strong or weak.
> So,I test the ChangeWatcher instance is real be gced. If the chain's length is only 1,the
useWeakReference works, the ChangeWatcher instance will be gced,but if the chain's length
is more than 1,the useWeakReference doesn't work.
> the source code:
> BindingUtils :
> public static function bindSetter(setter:Function, host:Object,
>                                       chain:Object,
>                                       commitOnly:Boolean = false,
>                                       useWeakReference:Boolean = false):ChangeWatcher
>     {
>         var w:ChangeWatcher =
>             ChangeWatcher.watch(host, chain, null, commitOnly, useWeakReference);
>         
>         if (w != null)
>         {
>             var invoke:Function = function(event:*):void
>             {
>                 setter(w.getValue());
>             };
>             w.setHandler(invoke);
>             invoke(null);
>         }
>         
>         return w;
>     }
> ChangeWatcher :
> public static function watch(host:Object, chain:Object,
>                                  handler:Function,
>                                  commitOnly:Boolean = false,
>                                  useWeakReference:Boolean = false):ChangeWatcher
>     {
>         if (!(chain is Array))
>             chain = [ chain ];
>         if (chain.length > 0)
>         {
>             var w:ChangeWatcher =
>                 new ChangeWatcher(chain[0], handler, commitOnly,
>                     watch(null, chain.slice(1), handler, commitOnly));     //there is
the reason!the default arg is false,so the 1st ChangeWatcher is "useWeakReference = true",but
others are "ChangeWatcher = false" 
>             w.useWeakReference = useWeakReference;
>             w.reset(host);
>             return w;
>         }
>         else
>         {
>             return null;
>         }
>     }
> I think the right code must be "watch(null, chain.slice(1), handler, commitOnly, useWeakReference));
 "
> the chain of ChangeWatchers will not be gced.

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