adobe flash buider (flex4): Error #2025 or Error: addChild() is not available in this class. Instead, use addElement()

I'm a complete newbie to Flex, so apologies for my dumbness. I've searched for an answer but haven't found anything that seems to be doing the trick.

What I'm trying to do: port this example http://www.adobe.com/devnet/air/flex/articles/flex_air_codebase_print.html to Flash Builder 4.

All seems to be fine but for one thing. When I use the original 开发者_C百科code for the Air application

<?xml version="1.0" encoding="utf-8"?>
<s:WindowedApplication 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="onApplicationComplete()">
<fx:Script>
    <![CDATA[
        private static const neededForCompilation:AirGeneralImplementation = null;
        private function onApplicationComplete():void
        {
            var can:MainCanvas = new MainCanvas();
            this.addChild(can); 
            can.labelMessage = "Loaded in an AIR Application ";
        }
    ]]>
</fx:Script>

<fx:Declarations>
    <!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>


</s:WindowedApplication>

I get this run time error

Error: addChild() is not available in this class. Instead, use addElement() or modify the skin, if you have one. at spark.components.supportClasses::SkinnableComponent/addChild()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\supportClasses\SkinnableComponent.as:1038]

If I substitute the code with

this.addElement(can);

Everything loads well but the first time I try to press any of the buttons on the main canvas I get the following run time error

ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller. at flash.display::DisplayObjectContainer/getChildIndex() at mx.managers::SystemManager/getChildIndex()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:1665] at mx.managers.systemClasses::ActiveWindowManager/mouseDownHandler()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\systemClasses\ActiveWindowManager.as:437]

here's the super simple code for the main canvas

<?xml version="1.0" encoding="utf-8"?>
<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" minWidth="955" minHeight="600"
               creationComplete="init();">
    <fx:Declarations>
        <!-- Place non-visual elements (e.g., services, value objects) here -->
    </fx:Declarations>
    <fx:Script source="main.as" />
    <mx:Label id="lblMessage" text="The UI from the shared Flex app BothCode" x="433" y="112"/>
    <s:Button x="433" y="141" click="saveFile();" label="Save File"/>
    <s:Button x="601" y="141" click="GeneralFactory.getGeneralInstance().airOnlyFunctionality();" label="Air Only"/>
</s:Application>

Any help would be immensely appreciated. And any pointers to how to setup a project that can compile in both Air and Flash while sharing the same code, all for Flex 4, would also be immensely appreciated.

thank you!

I ran into the same problem using that tutorial for Flex 4. I did the same thing as you and used the <s:Application> component for the Main Canvas. However the tutorial uses a <mx:VBox>, the solution I found was to change the Main Canvas from an <s:Application> to an <s:Group>. The problem seems to be embedding an Application within an Application.

The code on that link was written using the flex 3.5 sdk or below. You are using the new flex 4 sdk ( which is the default for Flash Builder ). You can do the following:
1. step into the code do any necessary changes to make it work for flex 4 sdk.
2. setup a new project using the flex 3 sdk ( select "Use a specific SDK" and choose the Flex 3 from the dropdown box in the "New Project" window)
I would suggest going for the second option, make it work and once you've stepped a little deeper into flex 4 you can do the 1st option.

Cheers.