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https://issues.apache.org/jira/browse/FLEX-12745?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13675462#comment-13675462
]
Mark Kessler commented on FLEX-12745:
-------------------------------------
Can reproduce issue with below test application. Mouse click on tab produces
one selectedtIndex change while the programmatic change produces the 3
selectedIndex changes.
<?xml version="1.0" encoding="utf-8"?>
<!---
Test application
-->
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009";
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx"
creationComplete="onCreationComplete();" >
<fx:Script>
<![CDATA[
import mx.binding.utils.BindingUtils;
protected function onCreationComplete():void
{
BindingUtils.bindSetter(bindingDest, theTabBar, "selectedIndex");
}
private function triggerBug():void
{
theTabBar.selectedIndex = 2;
//Note: trace() will also work wrong here - it will display old
value of selectedIndex, not the one that was just set above!
trace("triggerBug(): selectedIndex now = "+theTabBar.selectedIndex);
}
private function bindingDest(newVal:*):void
{
trace("bindingDest(): binding executed! newVal="+newVal);
}
]]>
</fx:Script>
<s:layout>
<s:VerticalLayout horizontalAlign="center" verticalAlign="middle"
gap="0" />
</s:layout>
<mx:TabBar id="theTabBar" dataProvider="{['Tab1', 'Tab2', 'Tab3']}"
selectedIndex="1" />
<mx:HRule />
<mx:Button label="Trigger bug" click="triggerBug()" />
</s:Application>
> TabBar: databinding executed three times when selectedIndex set
> programatically
> -------------------------------------------------------------------------------
>
> Key: FLEX-12745
> URL: https://issues.apache.org/jira/browse/FLEX-12745
> Project: Apache Flex
> Issue Type: Bug
> Components: mx: Tab Bar
> Affects Versions: Adobe Flex SDK 2.0.1 (Release)
> Environment: Affected OS(s): All OS Platforms
> Language Found: English
> Reporter: Adobe JIRA
> Labels: easytest
>
> Description:
> When TabBar's selectedIndex is changed programatically, any bindings to
> selectedIndex are executed three times: once with previous selectedIndex
> value, and twice with new value. Changing selectedIndex by clicking tabs with
> mouse works as expected though - bindings occur once.
> This bug will therefore cause all setters, <observe> tags etc watching
> selectedIndex property to be called 3x more than necessary, which - depending
> on their purpose - sometimes can be tolerated, but definitelly is not
> optimized.
> I noticed that bug when trying to find some workaround for another bug in
> TabBar (reported as SDK-13029). It ruined quite a good workaound I was
> testing :/
> Steps to reproduce:
> Run following code to see the bug
> <?xml version="1.0" encoding="utf-8"?>
> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"; layout="vertical"
> applicationComplete="initApp()" >
> <mx:TabBar id="theTabBar" dataProvider="{['Tab1', 'Tab2', 'Tab3']}"
> selectedIndex="1" />
> <mx:HRule />
> <mx:Button label="Trigger bug" click="triggerBug()" />
> <mx:Script>
> <![CDATA[
> import mx.binding.utils.BindingUtils;
> /**
> * Setup test binding
> * The same (triple call) behaviour would happen when
> binding with <mx:Binding> tag.
> */
> private function initApp():void {
> BindingUtils.bindSetter(bindingDest, theTabBar,
> "selectedIndex");
> }
>
> /**
> * Trigger TabBar bug: programatically change its
> selectedIndex.
> * Any bindings to selectedIndex will be executed three
> times:
> * - once with old selectedIndex value
> * - twice with new value
> */
> private function triggerBug():void {
> theTabBar.selectedIndex = 2;
> //Note: trace() will also work wrong here - it
> will display old value of selectedIndex, not the one that was just set above!
> trace("triggerBug(): selectedIndex now =
> "+theTabBar.selectedIndex);
> }
>
> /**
> * Example databinding target
> * Will be bound to TabBar's selectedIndex property.
> */
> private function bindingDest(newVal:*):void {
> trace("bindingDest(): binding executed!
> newVal="+newVal);
> }
>
> ]]
> >
> </mx:Script>
> </mx:Application>
>
> Actual Results:
> After selectedIndex is changed programatically, bindings to selectedIndex
> will be executed three times: once with previous selectedIndex value, and
> twice with new value.
>
> Expected Results:
> After selectedIndex is changed programatically, bindings to selectedIndex
> will be executed once, with new value (exactly the same behaviour as if tab
> was clicked by user with a mouse).
>
> Workaround (if any):
> None found.
>
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