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https://issues.apache.org/jira/browse/FLEX-33311?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Maxime Cowez resolved FLEX-33311.
---------------------------------
Resolution: Fixed
Fix Version/s: Apache Flex 4.9.0
Though no-one was assigned to this particular bug, apparently it has somehow
been fixed in 4.9
I have no idea what the possibly related issue(s) might be.
(I can still reproduce it in 4.8, so this is not due to "external" conditions
of my test application or anything.)
> Nullpointer in ConstraintLayout when executing Transition on content
> --------------------------------------------------------------------
>
> 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
> Priority: Trivial
> Fix For: Apache Flex 4.9.0
>
> Attachments: SpecifiableListWrapper.as,
> SpecifiableListWrapperHorizontalSkin.mxml
>
>
> In some very specific cases `ConstraintLayout` will throw a nullpointer 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 a nullpointer 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.
> Here is some code to reproduce the error consistently. My apologies for the
> complexity, but I couldn't get a simpler example to trigger the error.
> <s:Group width="100%">
> <s:layout>
> <s:ConstraintLayout>
> <s:constraintColumns>
> <s:ConstraintColumn id="sequenceCol"/>
> <s:ConstraintColumn id="labelCol"/>
> <s:ConstraintColumn id="contentCol" width="100%"/>
> <s:ConstraintColumn id="helpCol" maxWidth="200"/>
> </s:constraintColumns>
> <s:constraintRows>
> <s:ConstraintRow id="row1" baseline="maxAscent:10"
> height="100%"/>
> </s:constraintRows>
> </s:ConstraintLayout>
> </s:layout>
> <s:Group left="contentCol:0" right="contentCol:1" baseline="row1:0"
> bottom="row1:10">
> <t:SpecifiableListWrapper width="100%"
> skinClass="SpecifiableListWrapperHorizontalSkin">
> <s:DropDownList dataProvider="{dp}"/>
> </t:SpecifiableListWrapper>
> </s:Group>
> <s:Group id="helpContentGroup" left="helpCol:27" right="helpCol:10"
> bottom="row1:10" baseline="row1:0"/>
> </s:Group>
> As you may notice, the constraint columns and rows are a copy of those used
> in FormItemSkin. I left only the content columns necessary to trigger the
> error (yup, remove the `helpContentGroup` and the error's gone).
> SpecifiableListWrapper is a custom component which I will attach, along with
> the specific skin that has the Transition that triggers the error.
> Workaround: subclass ConstraintLayout (or FormItemLayout), override
> `measure()`, put a try/cacth block around it and use this custom layout.
> public class FormItemLayout extends spark.layouts.FormItemLayout {
> override public function measure():void {
> try {
> super.measure();
> }
> catch (e:Error) { }
> }
> }
> 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 >
> if (rowBaselines && rowBaselines[bIndex][1]) ...
> instead of
> if (rowBaselines[bIndex][1]) ...
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