Question

I have a TabNavigator with NavigatorContent’s in MXML. Inside the first NavigatorContent I have a Group with an id="canvas"; I load a SWFLoader here. Inside the next NavigatorContent I have another Group with the id="sheetcanvas"; I want to load a SWFLoader here. The problem is that when I do that I get error #1009 null reference on the sheetcanvas id.

If I take that same group and put it anywhere else it works with no null reference!

The same error occurs when loading dynamically to a second group that exists in a second NavigatorContent of an Accordion, also. Am I doing something wrong or is there a bug?

<mx:TabNavigator id="tabs" width="650" height="100%">
        <s:NavigatorContent width="100%" height="100%" label="Tab 1">
            <mx:DividedBox top="3" bottom="3" right="3" left="3" direction="vertical" width="100%" height="100%">

                <s:BorderContainer x="28" y="10" width="100%" height="100%">
                    <s:TextArea y="6" width="120" height="24" borderVisible="false"
                                text="{selectedNode.@label}"/>
                    <s:CheckBox y="6" right="10" label="Show Grid" selected="true"/>
                    <s:Scroller x="8" y="30" width="99%" height="90%" horizontalCenter="0">
                        <s:Group>
                            <s:Group id="canvas"/>

                        </s:Group>
                    </s:Scroller>
                </s:BorderContainer>
                <flexmd:FileEditor id="edit" width="100%" height="100%"
                                   enablePrint="true" enableSyntaxColoring="true" savePhp="/FileEditor/php/save.php"
                                   staticDemo="false"
                                   chromeColor="0xDCDCDC"
                                   />

            </mx:DividedBox>    
        </s:NavigatorContent>
        <s:NavigatorContent width="100%" height="100%" label="Tab 2">
            <mx:DividedBox top="3" bottom="3" right="3" left="3" direction="vertical" width="100%" height="100%">
                <s:BorderContainer x="28" y="10" width="100%" height="325">
                    <s:Scroller x="8" y="30" width="99%" height="100%" horizontalCenter="0">
                        <s:Group>
                            <s:Group id="scanvas"/>
                        </s:Group>
                    </s:Scroller>
                </s:BorderContainer>
            </mx:DividedBox>    
        </s:NavigatorContent>   
    </mx:TabNavigator>

Answer 1

It’s not a bug. Some containers (like TabNavigator or ViewStack) don’t initialize their child-elements until they are shown. If you need to have access to (hidden) child-elements right from the start, set the creationPolicy property to all.

Eg. <mx:TabNavigator id="tabs" width="650" height="100%" creationPolicy="all">

Here’s some more information about creationPolicy.