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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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Mihai Chira updated FLEX-33311:
-------------------------------
Attachment: Main.mxml
> 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
>
>
> 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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