[jira] [Commented] (FLEX-12745) TabBar: databinding executed three times when selectedIndex set programatically

["Mark Kessler (JIRA)" <ji...@apache.org>]

    [ 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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