Question

Reward: Has been claimed.

Overview: The code giving me the problem is deployed here: http://www.johnuckele.com/MastersOfTime.html

The problem I am running into is that a certain sequence of actions (I don’t fully understand how or why) is causing my calls to invalidateDisplayList to fail to produce a subsequent call to updateDisplayList. What I know is that during this period, some other visual effects will fail to occur (such as changing the width of a component or the addition of a new child).

Example: The program below draws two columns of horizontal lines. The column on the left is drawn during commitProperties, the column on the right is drawn during updateDisplayList. A certain sequence of actions can cause the right column to stop updating.

To trigger this bug: First add a new item. Now hit the start button and a bar starts filling up. If you press the add row button, the right column and the filling bar both stop growing. The left column continues unfettered. The extra component won’t appear until the last line of the if statement in TEComputeRow.tick() doesn’t execute for a frame. Click on the stop button to halt the execution of the block inside the if statement in TEComputeRow.tick() and everything goes back to normal.

Question: What is going on here?

I can force it to behave by using validate now but it doesn’t cure the problem, it merely covers it up for a frame. It also seems like a really sloppy hack. Is there a nicer way to deal with the loss of updateDisplayList than using validateNow? Are there any ways to accurately identify the state of the world?

MastersOfTime.mxml

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
    layout="absolute"
    backgroundColor="white"
    backgroundGradientAlphas="[1,1]"
    initialize="init()"
    enterFrame="tick()"
    creationComplete="addComputeArray()">
    <mx:Script>
        <![CDATA[
            import mx.containers.HBox;
            import mx.controls.Button;
            import mx.containers.VBox;
            import flash.utils.getTimer;
            private var global:int = 0;

            private function addComputeArray():void
            {
                var addButton:Button = new Button;
                addButton.label = "Add Row Item";
                addButton.addEventListener(MouseEvent.CLICK, addComputeBox);
                box.addChild(addButton);
            }

            private function addComputeBox(a:* = null):void
            {
                box.addChild(new TEComputeRow());
            }

            private function init():void
            {
                box.clipContent = false;
                box.graphics.lineStyle(1);
            }

            private function tick():void
            {
                global++;
                this.invalidateDisplayList();
                this.invalidateProperties();
                //this.validateNow();
            }
            protected override function commitProperties():void
            {
                super.commitProperties();
                box.graphics.moveTo(100, (global*3)%800);
                box.graphics.lineTo(200, (global*3)%800);
            }
            protected override function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void
            {
                super.updateDisplayList(unscaledWidth, unscaledHeight);
                box.graphics.moveTo(200, (global*3)%800);
                box.graphics.lineTo(300, (global*3)%800);
            }
        ]]>
    </mx:Script>
    <mx:VBox id="box"/>
</mx:Application>

TEComputeRow.mxml

<?xml version="1.0" encoding="utf-8"?>
<mx:VBox xmlns:mx="http://www.adobe.com/2006/mxml"
    height="60"
    width="352"
    verticalGap="0"
    borderStyle="solid"
    enterFrame="tick()">
    <mx:Script>
        <![CDATA[
            public var doStuff:Boolean = false;
            private var parameter:Number = 0;

            private function tick(e:Event = null):void
            {
                var value:*;
                if(doStuff)
                {
                    parameter = parameter+1;

                    value = parameter;

                    fill.width = value;
                }
            }
        ]]>
    </mx:Script>
    <mx:Button label="turn on" click="{doStuff = true;}" height="20"/>
    <mx:Container id="fill" x="7" width="0" height="20" backgroundColor="0x8888AA"/>
    <mx:Button label="turn off" click="{doStuff = false;}" height="20"/>
</mx:VBox>

Answer 1

The use of .width is what is triggering this problem. If I replace .width with .setActualSize the problem stops. These pieces of code travel through separate paths and .width and .height apparently have the capacity to skip part of the frame cycle (the updateDisplayList part).