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From "Mihai Chira (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLEX-33311) Nullpointer in ConstraintLayout when executing Transition on DropDownList
Date Wed, 17 Aug 2016 16:40:20 GMT

    [ https://issues.apache.org/jira/browse/FLEX-33311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15424860#comment-15424860
] 

Mihai Chira commented on FLEX-33311:
------------------------------------

I had just the same solution in mind, except with different places to increment and decrement
the counter. I managed to create a unit test to reproduce the bug, tested both our placings,
and both fix the bug. Yours are clearer and more logical, so I used them. Thank you for taking
a look!

> Nullpointer in ConstraintLayout when executing Transition on DropDownList
> -------------------------------------------------------------------------
>
>                 Key: FLEX-33311
>                 URL: https://issues.apache.org/jira/browse/FLEX-33311
>             Project: Apache Flex
>          Issue Type: Bug
>          Components: Spark: Layout, Transitions
>    Affects Versions: Apache Flex 4.8 (parity release)
>            Reporter: Maxime Cowez
>            Assignee: Mihai Chira
>             Fix For: Apache Flex 4.9.0
>
>         Attachments: Main.mxml, SpecifiableListWrapper.as, SpecifiableListWrapperHorizontalSkin.mxml,
stack.xml
>
>
> In some very specific cases {{ConstraintLayout}} will throw a null pointer error when
a component inside it is playing a transition. I tried a few things and found out that:
> * {{parseConstraints()}} creates a new {{rowBaselines}} Vector (or empties it if it exists)
> * some other process calls {{clearConstraintCache()}} in the middle of the execution
of {{parseConstraints()}}, setting {{rowBaselines}} back to {{null}}
> * {{parseConstraints()}} calls {{parseElementConstraints()}} which tries to access elements
in {{rowBaselines}} and throws the error
> I know very little about how Effects and Transitions work, so the "some other process"
part is a bit of a mistery to me.
> *Steps to reproduce*:
> # Compile and run Main.mxml
> # Select the first item in the list
> # Click on the list and, before the resize transition finishes, click on it again.
> *Workaround*: subclass ConstraintLayout (or FormItemLayout), override `measure()`, put
a try/cacth block around it and use this custom layout. Not exactly pretty but it works without
apparent side effects.
> *Quick fix* (but probably not the ideal solution): just test whether {{rowBaselines}}
exists before trying to access it in {{ConstraintLayout.parseElementConstraints()}}.



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