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Posted to dev@flex.apache.org by "Maxime Cowez (JIRA)" <ji...@apache.org> on 2012/12/17 17:41:11 UTC
[jira] [Updated] (FLEX-33311) Nullpointer in ConstraintLayout when
executing Transition on content
[ https://issues.apache.org/jira/browse/FLEX-33311?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Maxime Cowez updated FLEX-33311:
--------------------------------
Attachment: SpecifiableListWrapperHorizontalSkin.mxml
SpecifiableListWrapper.as
Custom component and skin to recreate the error.
> 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
> 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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