TextEventの練習C

/**
 * Copyright tsu_droid ( http://wonderfl.net/user/tsu_droid )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/2qia
 */

package {
    import flash.display.Sprite;
    import flash.text.TextField;
    import flash.text.TextFieldType;
    import flash.text.TextFieldAutoSize;
    import flash.events.TextEvent;

    public class TextEvent_TEXT_INPUTExample extends Sprite {
        private var instructionTextField:TextField = new TextField();
        private var inputTextField:TextField = new TextField(); 
        private var warningTextField:TextField = new TextField();
        private var result:String = "";

        public function TextEvent_TEXT_INPUTExample() {
            instructionTextField.x = 10;
            instructionTextField.y = 10;
            instructionTextField.background = true; 
            instructionTextField.autoSize = TextFieldAutoSize.LEFT;
            instructionTextField.text = "Please enter a value in the format A#AA#AA,\n" 
                                        + "where 'A' represents a letter and '#' represents a number.\n" +
                                        "(Note that once you input a character you can't change it.)" ;
        
            inputTextField.x = 10;
            inputTextField.y = 70;
            inputTextField.height = 20;
            inputTextField.width = 75;
            inputTextField.background = true;
            inputTextField.border = true;
            inputTextField.type = TextFieldType.INPUT; 
            
            warningTextField.x = 10;
            warningTextField.y = 100;
            warningTextField.autoSize = TextFieldAutoSize.LEFT;
 
            inputTextField.addEventListener(TextEvent.TEXT_INPUT, textInputHandler);   
           
            this.addChild(instructionTextField);
            this.addChild(inputTextField);
            this.addChild(warningTextField);
        }

        private function textInputHandler(event:TextEvent):void {
            var charExp:RegExp = /[a-zA-z]/;   
            var numExp:RegExp = /[0-9]/;

            event.preventDefault();  
            
            inputTextField.text = result;                
            inputTextField.setSelection(result.length + 1, result.length + 1);
 
            if (inputTextField.text.length == 1 || inputTextField.text.length == 4) {
            
                if(numExp.test(event.text) == true) {
                    updateCombination(event.text);
                } else {
                    warningTextField.text = "You need a single digit number.";
                }
               
            }else {
                
                if(charExp.test(event.text) == true) { 
                    updateCombination(event.text);
                } else {
                    warningTextField.text = "You need an alphabet character.";
                }
            }
 
            if(inputTextField.text.length == 7) {
                inputTextField.type = TextFieldType.DYNAMIC;
                instructionTextField.text = "CONGRATULATIONS. You've done.";                
            }          
        }

        private function updateCombination(s:String):void {
                    warningTextField.text = "";
                    result += s;           
                    inputTextField.text = result;
                    inputTextField.setSelection(result.length + 1, result.length + 1);
        }
    }
}