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From "Alex Harui (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLEX-27837) ChangeWatcher bug
Date Mon, 23 Sep 2013 04:18:02 GMT

    [ https://issues.apache.org/jira/browse/FLEX-27837?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13774283#comment-13774283
] 

Alex Harui commented on FLEX-27837:
-----------------------------------

IMO, the code is correct.  Please provide a test case that indicates differently.  It is true
that the documentation should be different: the weakReference parameter determines if the
reference from the host to the ChangeWatcher is strong or weak, so there's an "essyfix" to
change the documentation.

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.

The reason a chain of ChangeWatchers are not available for GC is that the 'next' property
of the ChangeWatcher forms a hard reference chain of ChangeWatchers.  The point of the weakReference
parameter is to make sure the ChangeWatchers aren't pinned in memory by the host and other
objects in the chain, but as long as you have a strong reference to a ChangeWatcher all of
remainder of that chain appears to be pinned in memory as well, just not by the host and other
objects.
                
> 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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