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https://issues.apache.org/jira/browse/FLEX-33629?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mihai Chira updated FLEX-33629:
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Attachment: _DropDownDoubleBound.fxp
> Is this the expected (and planned for the future) behaviour for a
> dropdownlist with its selectedItem two-way bound and set before the data
> provider?
> ----------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: FLEX-33629
> URL: https://issues.apache.org/jira/browse/FLEX-33629
> Project: Apache Flex
> Issue Type: Question
> Components: Spark: DropDownList
> Affects Versions: Apache Flex 4.9.0
> Reporter: Mihai Chira
> Priority: Critical
> Attachments: _DropDownDoubleBound.fxp
>
>
> Run the attached application, and press one of the two buttons on the left.
> Actual behaviour: the selectedItem should represent the owner of that job,
> but it's now wrong because the selectedItem has been assigned before the
> dataProvider, so the first item in the list has been selected (and set in the
> model) instead, because requireSelection was "true" in the dropdownlist.
> Desired behaviour: not sure, but modifying the model with invalid data
> because of the timing of assignments in a visual component (so without any
> user input) feels unintended and definitely surprising. We have lots of forms
> in our application, and the team spent an aggregate of around two weeks
> chasing various bugs that all came down to the timing between assigning
> selectedItem and dataProvider in dropdowns.
> A few suggestions:
> -to keep the problem discoverable, but not mess up the model, there could be
> an additional property on the dropdownlist called userSelectedItem, to which
> the developers could safely bind two-ways, as the trigger would only fire for
> the "change" event - thus, when the user selects an item from the list.
> Please see ExtendedDropDownList in the project for an example. When we bind
> to userSelectedItem, the selection in the dropdown is still wrong, but the
> model is intact (replace DropDownList with ExtendedDropDownList in
> _DropDownDoubleBound.mxml and two-way bind to userSelectedItem instead of
> selectedItem).
> -the binding trigger event could be "change" instead of "valueCommit"
> ("dispatchEvent(new FlexEvent(FlexEvent.VALUE_COMMIT));" in
> ListBase.commitSelection() seems to trigger the bindings now.)
> -the DropDownList could throw an error when the selectedItem cannot be found
> in the dataProvider.
> All the potential solutions above have benefits and drawbacks, but I guess it
> might be a good idea to start a discussion on what the best direction could
> be for this issue.
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