Flex AIR compile error access of undefined property - apache-flex

Question

Working through a series of Adobe AIR examples I have encountered a compilation error with one of them that I have distilled into the following demo application file
<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication
xmlns:mx="http://www.adobe.com/2006/mxml">
<mx:Script>
<![CDATA[
import mx.events.MenuEvent;
private static const MENU_DEMO:String = "Demo...";
private function onMenuItemClick(evt:MenuEvent):void
{
switch(evt.label)
{
case MENU_DEMO:
break;
}
}
]]>
</mx:Script>
<mx:VBox width="100%" height="100%" paddingBottom="5">
<mx:MenuBar id="menuBar"
width="100%"
labelField="#label"
itemClick="onMenuItemClick(event);">
<mx:XMLList>
<menuitem label="Error">
<menuitem label="{MENU_DEMO}" />
</menuitem>
</mx:XMLList>
</mx:MenuBar>
</mx:VBox>
</mx:WindowedApplication>
for which the descriptor file is
<?xml version="1.0" encoding="UTF-8"?>
<application xmlns="http://ns.adobe.com/air/application/1.0.M6">
<id>ErrorDemo</id>
<filename>ErrorDemo</filename>
<name>Error Demo</name>
<version>v0.1</version>
<description>Demo undefined property error</description>
<copyright></copyright>
<initialWindow>
<title>Error Demo</title>
<content>ErrorDemo.swf</content>
<systemChrome>standard</systemChrome>
<transparent>false</transparent>
<visible>true</visible>
</initialWindow>
</application>
Compilation produces the following output
C:\Projects\AIR\ErrorDemo>amxmlc ErrorDemo.mxml
Loading configuration file C:\Projects\flex_sdk_4.6\frameworks\air-config.xml
C:\Projects\AIR\ErrorDemo\ErrorDemo.mxml(28): Error: Access of undefined property _ErrorDemo_XMLList1.
<menuitem label="{MENU_DEMO}" />
The problem seems to be down to the use of the static const {MENU_DEMO} bound to the menuitem tag's label attribute because substituting it with text leads to no compilation error. Adobe's Using Flex 4.6 documentation states that static constants can be used as data binding sources, but maybe not in the way they're used here. Does anyone know what the problem is with using them in this way?
To clarify: replacing the bound constant reference {MENU_DEMO} with the string literal Demo... produces the following expected output. But using a string literal in place of the bound constant reference defeats the purpose of using a bound constant. Which is what seems to generate the error, and is the point of this post.

Answer 1

try adding [Bindable] before private static const MENU_DEMO:String = "Demo...";
it becomes:
[Bindable]
private static const MENU_DEMO:String = "Demo...";

Answer 2

I don't use Flex but from some research about your problem I noticed...
(1)
Your code has:
<menuitem label="{MENU_DEMO}" />
Try setting that as:
<menuitem label text="{MENU_DEMO}" />
(2)
Also since you say itemClick="onMenuItemClick(event);" shouldn't that be backed up by:
import mx.events.ItemClickEvent;
(3)
What is the expected result if your code compiled correctly?
I can't (or won't) test any Flex code so let me know if this works or errors...
<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication
xmlns:mx="http://www.adobe.com/2006/mxml">
<mx:Script>
<![CDATA[
import mx.events.MenuEvent;
import mx.events.ItemClickEvent; //add this
[Bindable]
public var MENU_DEMO:String = "Demo...";
public function onMenuItemClick(evt:MenuEvent):void //or try... (evt:MenuEvent = null):void
{
if (evt.label.text == MENU_DEMO) //untested
{
//do something here
evt.label.text = "Changed...";
}
}
]]>
</mx:Script>
<mx:VBox width="100%" height="100%" paddingBottom="5">
<mx:MenuBar id="menuBar"
width="100%"
labelField="#label"
itemClick="onMenuItemClick(event);">
<mx:XMLList xmlns="">
<menuitem label="Error" />
<menuitem label text="{MENU_DEMO}" />
</menuitem>
</mx:XMLList>
</mx:MenuBar>
</mx:VBox>
</mx:WindowedApplication>

Answer 3

For anyone interested in what a Flex 4 version of the mxml code looks like, here is what I came up with, following #ProgrammerDancuk's suggestion, who really should receive credit
<?xml version="1.0" encoding="utf-8"?>
<s:WindowedApplication
xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:mx="library://ns.adobe.com/flex/mx"
xmlns:s="library://ns.adobe.com/flex/spark">
<fx:Script>
<![CDATA[
import mx.events.MenuEvent;
private static const MENU_DEMO:String = "Demo...";
private function onMenuItemClick(evt:MenuEvent):void
{
switch(evt.label)
{
case MENU_DEMO:
break;
}
}
]]>
</fx:Script>
<fx:Declarations>
<!-- Place non-visual elements (e.g., services, value objects) here -->
<fx:XMLList id="demoMenu">
<menuitem label="Error">
<menuitem label="{MENU_DEMO}" />
</menuitem>
</fx:XMLList>
</fx:Declarations>
<mx:VBox width="100%" height="100%" paddingBottom="5">
<mx:MenuBar id="menuBar"
width="100%"
labelField="#label"
itemClick="onMenuItemClick(event);">
<mx:dataProvider>
{demoMenu}
</mx:dataProvider>
</mx:MenuBar>
</mx:VBox>
</s:WindowedApplication>