Flex / ActionScript3 - Object Attribute / Variable null - apache-flex

Question

If I execute the code below in FlashBuilder, I get the following error (I translate it)
TypeError: Error #1009: Access to an Attribute or Method of an null-Object is not possible.
at components::NumDisplay()[\src\components\NumDisplay.mxml:39]
This line in NumDisplay.mxml is the problem:
[Bindable]
public var oneled_top:OneDisplay = new OneDisplay(numberData.led_top);
If i change it from the above to:
[Bindable]
public var oneled_top:OneDisplay = new OneDisplay(1);
It is working, because I send a real Number.
So how can I access the value from numberData.led_top?
If I test the access in the samefile NumDisplay.mxml with the line
<s:Label text="{numberData.led_top}" color="#FF0000">
</s:Label>
it accesses the value, the same as if I put it in my component
<components:oneLedDisplay showData="{numberData.led_top}" x="10" y="10" />
I don't get it after searching a couple of hours...
Thanks in advance.
My main method tasachenrechner.mxml:
<?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="600" minHeight="500" xmlns:components="components.*">
<fx:Script>
<![CDATA[
import components.NumberDisplay;
[Bindable]
protected var firstNumber:NumberDisplay = new NumberDisplay(1);
[Bindable]
protected var secondNumber:NumberDisplay = new NumberDisplay(2);
]]>
</fx:Script>
<components:NumDisplay
numberData="{firstNumber}"
x="10"
y="20"/>
<components:NumDisplay
numberData="{secondNumber}"
x="73"
y="20"/>
</s:Application>
My AS-Class NumberDisplay.as:
package components
{
import flash.display.DisplayObject;
[Bindable]
public class NumberDisplay
{
public var num:Number;
public var led_top:Number=0;
public var led_r1:Number=0;
public var led_r2:Number=0;
public var led_middle:Number=0;
public var led_l1:Number=0;
public var led_l2:Number=0;
public var led_bottom:Number=0;
public function NumberDisplay(num:Number)
{
this.num = num;
switch(this.num)
{
case 0:
trace("ZERo");
break;
case 1:
led_top = 1;
led_r1 = 1;
led_r2 = 1
trace("EINS" + led_top + " num:" + num);
break;
//[... some more cases]
default:
break;
}
}
}
}
My NumDisplay.mxml:
<?xml version="1.0" encoding="utf-8"?>
<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx" width="45" height="59"
xmlns:components="components.*">
<fx:Style>
#namespace s "library://ns.adobe.com/flex/spark";
#namespace mx "library://ns.adobe.com/flex/mx";
#namespace components "components.*";
</fx:Style>
<fx:Script>
<![CDATA[
import components.NumberDisplay;
import components.OneDisplay;
[Bindable]
public var numberData:NumberDisplay;
[Bindable]
public var oneled_top:OneDisplay = new OneDisplay(numberData.led_top);
// some more init calls of data-objects same type
]]>
</fx:Script>
<s:Label text="{numberData.led_top}" color="#FF0000">
</s:Label>
<components:oneLedDisplay showData="{oneled_top}" x="10" y="10" />
// some more objects of same type
</s:Group>
My AS-Class OneDisplay.as:
package components
{
import flash.display.DisplayObject;
public class OneDisplay
{
[Bindable]
public var show:Number;
[Bindable]
public var value:Number=0;
public function OneDisplay(show:Number)
{
this.show = show;
switch(this.show)
{
case 0:
value = 0.3;
trace(value);
break;
case 1:
value = 1.0;
trace(value);
break;
}
}
}
}
My oneLedDisplay.mxml:
<?xml version="1.0" encoding="utf-8"?>
<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx">
<fx:Script>
<![CDATA[
import components.OneDisplay;
[Bindable]
public var showData:OneDisplay;
]]>
</fx:Script>
<s:Rect id="stroke" width="40" height="6" alpha="{showData.value}">
<s:fill>
<s:SolidColor color="#000000"/>
</s:fill>
</s:Rect>
<s:Label text="{showData.value}" color="#FF0000">
</s:Label>
</s:Group>

Answer 1

Remember that you are not only assigning a value, but declaring the member variable oneled_top. At that point, you cannot access numberData because it has not been instantiated (there is no call to new NumberData()! You have to find a way to make your call to new OneDisplay (numberData.led_top) at a later time, when there actually is a value to access.

Answer 2

You provided lots of code which I don't want to reverse engineer.
The answer is that oneled_top is being initialized before numberData. You have no control over initialization of variables when using MXML.
Set default values in the commitProperties() method, or if oneled_Top is supposed to be a skin part, set the default values in the PartAdded method.
You'll benefit from reading up on the Component Lifecycle.

Answer 3

You can use BindingUtils.bindSetter() to detect changes to numberData and then initialize oneled_top
BindingUtils.bindSetter(_setOneLabel_top, this, "numberData");
and setter:
function _setOneLabel_top(disp:NumberDisplay):void
{
/* if(this.oneled_top == null) */
this.oneled_top = new OneDisplay(disp.led_top);
}
But I think, that u're using [Bindable] where you shouldn't have to need it.