Maxime Cowez created FLEX-33311:
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Summary: 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
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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