Input text issue in my Keyboard ActionScript 2.0 class

Greetings, I'm currently trying to code a Keyboard screen display here. The only thing I'm having trouble with is the input's text field which is my own input text I created: this._input._field.text:

class Keyboard extends MovieClip
{
	var remote;
	var _field;
	var _input;
	var _a;
	var _b;
	var _c;
	var _d;
	var _e;
	var _f;
	var _g;
	var _h;
	var _i;
	var _j;
	var _k;
	var _l;
	var _m;
	var _n;
	var _o;
	var _p;
	var _q;
	var _r;
	var _s;
	var _t;
	var _u;
	var _v;
	var _w;
	var __x;
	var __y;
	var _z;
	var _one;
	var _two;
	var _three;
	var _four;
	var _five;
	var _six;
	var _seven;
	var _eight;
	var _nine;
	var _zero;
	var _start;
	var profileBuildAlert;
	static var _instance;
	function Keyboard()
	{
		super();
		this.init();
	}
	function init()
	{
		this.remote = platform.nintendo.wii.WiiRemote.getInstance(platform.nintendo.wii.WiiRemote.REMOTE_1);
		this.profileBuildAlert._visible = false;
		this.profileBuildAlert.enabled = false;
		this._start._visible = false;
		this._start.enabled = false;
		this.buildKeyboard();
	}
	function buildKeyboard()
	{
		var shim = this;
		var buttons = [{button:this._one, label:"1"}, {button:this._two, label:"2"}, {button:this._three, label:"3"}, {button:this._four, label:"4"}, {button:this._five, label:"5"}, {button:this._six, label:"6"}, {button:this._seven, label:"7"}, {button:this._eight, label:"8"}, {button:this._nine, label:"9"}, {button:this._zero, label:"0"}, {button:this._a, label:"A"}, {button:this._b, label:"B"}, {button:this._c, label:"C"}, {button:this._d, label:"D"}, {button:this._e, label:"E"}, {button:this._f, label:"F"}, {button:this._g, label:"G"}, {button:this._h, label:"H"}, {button:this._i, label:"I"}, {button:this._j, label:"J"}, {button:this._k, label:"K"}, {button:this._l, label:"L"}, {button:this._m, label:"M"}, {button:this._n, label:"N"}, {button:this._o, label:"O"}, {button:this._p, label:"P"}, {button:this._q, label:"Q"}, {button:this._r, label:"R"}, {button:this._s, label:"S"}, {button:this._t, label:"T"}, {button:this._u, label:"U"}, {button:this._v, label:"V"}, {button:this._w, label:"W"}, {button:this.__x, label:"X"}, {button:this.__y, label:"Y"}, {button:this._z, label:"Z"}];
		for (var i = 0; i < buttons.length; i++)
		{
			var button = buttons[i].button;
			var label = buttons[i].label;
			button._field.text = label;
			button.onRelease = function()
			{
				shim.remote.startVibrate(50,200,3);
				shim.displayInInput(this._field.text);
			};
			button.onRollOver = function()
			{
				shim.remote.startVibrate(50,200,3);
				this._field._width = 30.35;
				this._field._height = 43.35;
				this._field._x = 4.25;
				this._field._y = -1.15;
				this.icon._width = 45;
				this.icon._height = 45;
				this.icon._x = -2;
				this.icon._y = -2;
			};
			button.onReleaseOutside = button.onRollOut = function ()
			{
				shim.remote.startVibrate(50,200,3);
				this._field._width = 28;
				this._field._height = 40;
				this._field._x = 5.75;
				this._field._y = 0.75;
				this.icon._width = 41.5;
				this.icon._height = 41.5;
				this.icon._x = 0;
				this.icon._y = 0;
			};
		}
	}
	function displayInInput(input)
	{
		this._input._field.text = input;
		if (this._input._field.text.length > 0)
		{
			this._start._visible = true;
			this._start.enabled = true;
		}
	}
}

on the displayInInput text function, if I do: this._input._field.text = input; Clicking on any number or letter button will display only one letter or number in the _input._field.text, but if I do: += input, the _input._field.text won't display anything. What I want fix and the correction here in my code is when users click letters or numbers or both, then they both get displayed in the _input._field.text like this:

for example, if I want to type in: SAMPLE, I would click on the S,A,M,P,L, and E buttons. Finally the _input._field.text says: SAMPLE, not a just single letter or a number in the input.