Giving event functions to a MC

I have a myFile MC that loads a JPG using my_mc.loadClip(run_url, “myFile”);.then, I want to add some interaction, like:

myFile.onEnterFrame = function () {
trace (“bap”);
}

but it doesn’t work. Why is that? Does the loadClip code disables the MC’s main commands?

import mx.utils.Delegate; //helps to manage scope issues within callback functions

var streamingID:Number;
var fileLoaded:Boolean;
var dBar:MovieClip = this.Bars.dBar; //downloading bar
var progBarFactor = dBar._width/100; //pixel to percents
var space:Number = 50;
var proportion:Number;
var actualW:Number;
var actualH:Number;
var actualSize:Boolean = false;

function displayStreaming (theSource:Object) {
    //check to see if track has finished downloading:
    if (fileLoaded) {
        clearInterval (streamingID);
        dBar._x = dBar._width;
    } else {
        var percentLoaded:Number = Math.floor((theSource.getBytesLoaded()/ theSource.getBytesTotal())*100);
        dBar._x = percentLoaded*progBarFactor;
    }
}

function doneStreaming():Void {
    fileLoaded = true;
}

MovieClip.prototype.screenFit = function(){
    actualW = this._width;
    actualH = this._height;
    if ((this._width/this._height) > (Stage.width/Stage.height)) {
        if (this._width > Stage.width - space*2) {
            proportion = (this._height / this._width);
            this._width = Stage.width - space*2;
            this._height = this._width * proportion;
        }
    } else {
        if (this._height > Stage.height - space) {
            proportion = (this._width / this._height);
            this._height = Stage.height - space*2;
            this._width = this._height * proportion;
        }
        this._x = (Stage.width - this._width)/2;
        this._y = (Stage.height - this._height)/2;
    }
    mask._x = this._x; mask._y = this._y;
    mask._width = this._width;
    mask._height = this._height;
    delete onEnterFrame;
};

MovieClip.prototype.actualSize = function(){
    this._height = actualH;
    this._width = actualW;
    this._x = (Stage.width - this._width)/2;
    this._y = (Stage.height - this._height)/2; 
    if (this._width < Stage.width - space*2) {
        mask._width = this._width;
        mask._x = this._x;
    } else {
        mask._width = Stage.width - space*2;
        mask._x = space;
    }
    if (this._width < Stage.width - space*2) {
        mask._height = this._height;
        mask._y = this._y;
    } else {
        mask._height = Stage.height - space*2;
        mask._y = space;
    }
}

myFile.onEnterFrame = function () {
    trace ("bap");
    if (actualSize == true && _xmouse > _parent.mask._x && _xmouse < _parent.mask._x + _parent.mask._width && _ymouse > _parent.mask._y && _ymouse < _parent.mask._y + _parent.mask._height) {
        K = (_xmouse - _parent.mask._x) / (_parent.mask._x + _parent.mask._width - _xmouse);
        targetX = _xmouse - K * this._width / (K+1);
        K = (_ymouse - _parent.mask._y) / (_parent.mask._y + _parent.mask._height - _ymouse);
        targetY = _ymouse - K * this._height / (K+1);
        speed = 5;
        this._x += (targetX - this._x) / speed;
        this._y += (targetY - this._y) / speed;
    }
}

fileLoaded = false;
my_mc = new MovieClipLoader();
my_mc.loadClip(run_url, "myFile");
my_mc.onLoadComplete = Delegate.create(this, doneStreaming);
streamingID = setInterval (displayStreaming, 100, myFile);

onEnterFrame = function(){
    if (fileLoaded){
        myFile.screenFit();
    }
}


stop();