Problem with changing textfield content

programming flash
1

Hi,
I’m new to AS3 classes and try to change the content of the textfield.
Could someone give me a tip to get this to work. Thanks

Documentclass dispatchEventExample.as


package {
    import flash.display.MovieClip;
    import flash.events.Event;

    import TextfieldMessage;
      
    public class dispatchEventExample extends flash.display.MovieClip {

        // Constructor
        public function dispatchEventExample():void {
 
            // Add new Instance to stage
            var textMessageInstanz:TextfieldMessage = new TextfieldMessage("Hello");
            addChild(textMessageInstanz);
            textMessageInstanz.x=20;
            textMessageInstanz.y=20;
             
            // Add event listener
            textMessageInstanz.addEventListener(TextfieldMessage.LISTITEM_CLICK, showText);
 
            function showText(evt:Event):void {
                
                textMessageInstanz.TextString ="Goodbye";
                this.text=textMessageInstanz.TextString;
                                
                // This line gives me:  1119: Access of possibly undefined property
                // textMessageInstanz.text = "Goodbye";
                
                // This property works fine
                textMessageInstanz.x += 5;                
                                
                trace(textMessageInstanz.TextString);
                            
            }
        }
    }
}

TextfieldMessage.as


package {
    import flash.display.Sprite;
    import flash.text.TextField;
    import flash.events.*;
  
    public class TextfieldMessage extends Sprite {
 
        // TextfiedMessage-Event
        public static const LISTITEM_CLICK:String="MY_TEXTFIELD_EVENT";
 
        // Vars
        protected var selectedTextfieldText:String;
         private var myVar:String;
 
        public function TextfieldMessage(string:String) {
            
            myVar = string;            

            // Textfield
            var lblText:TextField = new TextField();
            lblText.mouseEnabled=true;
             lblText.selectable=false;
            lblText.width=225;
            lblText.height=26;
            lblText.text="Test: " + myVar;
            
            lblText.addEventListener(MouseEvent.CLICK, Click);
            addChild(lblText);
        }
 
        // Getter function
        public function get TextString():String {
            // return selectedTextfieldText;
            return this.myVar;
        }
         
        // Setter function
        public function set TextString(value:String):void{
            this.myVar = value;
        } 
 
        // Event listener
        public function Click(evt:MouseEvent):void {
            selectedTextfieldText=evt.currentTarget.text;
            trace("Click: " + evt.currentTarget.text)
            dispatchEvent(new Event(LISTITEM_CLICK));
        } 
    }
}