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Adobe AIR Development

New Developer
Posts: 34
Registered: ‎03-23-2011
My Device: Bold 9700
My Carrier: Rogers
Accepted Solution

Problem setting focus - stage is null?

I'm trying to programmatically set the focus of a textinput however the debugger is throwing me this error:


Cannot access a property or method of a null object reference.


I'm trying to set the focus with this line:


stage.focus = input;


For reference here is a bit of the code:


package views
	import flash.display.GradientType;
	import flash.display.Graphics;
	import flash.display.Shape;
	import flash.events.MouseEvent;
	import flash.events.TouchEvent;
	import flash.geom.Matrix;
	import flash.text.TextFormat;
	import flash.text.TextFormatAlign;
	import qnx.input.IMFConnection;
	import qnx.ui.buttons.LabelButton;
	import qnx.ui.core.UIComponent;
	import qnx.ui.display.Image;
	import qnx.ui.text.Label;
	import qnx.ui.text.TextInput;

	public class RenamePopupContainer extends UIComponent
		private var input:TextInput;
		private var file:String;
		public function RenamePopupContainer(_file:String)
			file = _file;
			setSize(1024, 600);
			setPosition(0, 0);
			stage.focus = input;
		private function createChildren():void
			var labelFormat:TextFormat = new TextFormat();
			labelFormat.color = 0xFFFFFF;
			labelFormat.size = 28;
			labelFormat.align = TextFormatAlign.CENTER;
			var mat:Matrix = new Matrix();
			mat.createGradientBox(400, 1);
			var line1:Shape = new Shape();
			line1.x = 312;
			line1.y = 92;
			line1.graphics.beginGradientFill(GradientType.LINEAR, [0xeeeeee, 0xeeeeee, 0xeeeeee], [0, 1, 0], [0, 127, 255], mat);
			line1.graphics.drawRect(0, 0, 400, 1);
			var label:Label = new Label();
			label.text = "Rename to?";
			label.setSize(450, 40);
			label.setPosition(287, 43);
			label.format = labelFormat;
			input = new TextInput();
			input.setSize(380, 40);
			input.setPosition(322, 120);
			input.text = file;
			var line2:Shape = new Shape();
			line2.x = 312;
			line2.y = 190;
			line2.graphics.beginGradientFill(GradientType.LINEAR, [0xeeeeee, 0xeeeeee, 0xeeeeee], [0, 1, 0], [0, 127, 255], mat);
			line2.graphics.drawRect(0, 0, 400, 1);
			var btnOk:LabelButton = new LabelButton();
			btnOk.setSize(120, 40);
			btnOk.setPosition(384, 210);
			btnOk.label = "Ok";
			btnOk.addEventListener(MouseEvent.CLICK, ok);
			var btnCancel:LabelButton = new LabelButton();
			btnCancel.setSize(120, 40);
			btnCancel.setPosition(519, 210);
			btnCancel.label = "Cancel";
			btnCancel.addEventListener(MouseEvent.CLICK, cancel);


Posts: 6,473
Registered: ‎12-08-2010
My Device: PlayBook, Z10
My Carrier: none

Re: Problem setting focus - stage is null?

It's a fairly common problem: a DisplayObject's stage property is null until it has been added into the display list.  There are a few solutions, but the simplest for you might be this one, if this object will only ever be added to the display list once.


// in place of your existing stage.focus line
addEventListener(Event.ADDED_TO_STAGE, onAddedToStage);


private function onAddedToStage(e:Event):void {
    removeEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
    stage.focus = input;


Peter Hansen -- (BB10 and dev-related blog posts at http://peterhansen.ca.)
Author of White Noise and Battery Guru for BB10 and for PlayBook | Get more from your battery!
New Developer
Posts: 34
Registered: ‎03-23-2011
My Device: Bold 9700
My Carrier: Rogers

Re: Problem setting focus - stage is null?

THanks for the reply, but it only sort of worked.  If I set the focus from within the container, it doesn't actually set the focus, it creates a yellow box around the textinput, but doesn't automatically allow heyboard input.


If I make the textinput public and set the focus from outside the container, in the calling class, it properly focuses.


Is there a way, or something I'm missing, to set the focus from in the container?