Why am I unable to access the methods of an object via is ObjectContainer - actionscript-3

Question

first of all, i'm not a native english speaker but, still, i'll try my best to be understandable and as clear as possible.
So, in my programming class, I need to make a Tile based game (like zelda, for exemple) with animate cc (flash). On a map, I want to make a dance floor with tiles that changes on the rhythm of a music. these tiles are movieclip with two frame, one white and one red.
This is how the tiles are generated:
private function createGrid(): void {
grid = new MovieClip();
addChild(grid);
for (var r: int = 0; r < nbRow; r++) {
for (var c: int = 0; c < nbCol; c++) {
var t: Tiles = new Tiles();
t.x = t.width * c;
t.y = t.height * r;
grid.addChild(t);
}
}
grid.x = 15; //center the grid on x
grid.y = 35; //center the grid on y
}
This is the Tiles Class :
package {
import flash.display.MovieClip;
import flash.events.*;
public class Tiles extends MovieClip {
private var rand:int;
public function Tiles() {
// constructor code
getTiles();
}
public function getTiles():void {
random();
setColor();
}
private function random() : void{
rand = Math.floor(Math.random()*100)+1;
}
private function setColor() : void{
if(rand<=30){
gotoAndStop(8); //red frame
}else{
gotoAndStop(7); //white frame
}
}
}
}
createGrid() place the tiles as soon as the map is placed on the stage and stock every tiles in the MovieClip grid. Now, I want the tiles to change randomly between red and white on the beat of a streamed music (and keep the ratio of 30% red tiles and 70% white tiles)
var s: Sound = new Sound();
var sc: SoundChannel;
s.load(new URLRequest("GameSong_mixdown.mp3"));
sc = s.play(0, 1000);
I know i need the leftpeek properties of my soundchannel to achieve that but,for now, I do my test with a button that trigger this function:
private function setTiles(e: Event): void {
// loop through all child element of a movieclip
for (var i: int = 0; i < grid.numChildren; i++) {
grid.getChildAt(i).getTiles();
}
}
Right now, the problem is : I'm unable to acces my Tiles method. I did a trace on grid,getChildAt(i), and saw all instances of my tiles in the console. So, i know for sure that every instances of my tiles are stored in grid. But, I don't know why, grid.getChildAt(i).getTiles(); doesn't work (and every other method from Tiles). The error message is: Call to a possibly udefined method getTiles through a reference with static type flash.display:DisplayObject
Does someone know what i'm doing wrong ?
ps: I translated all my class name, var name, etc from french to
english to make the code clearer.

Answer 1

Your mistake is that getChildAt(...) method has a return type of DisplayObject which is neither dynamic (will not let you access random properties) nor it have DisplayObject.getTiles() method.
All you need is to tell the program that this object is actually of Tiles class:
private function setTiles(e:Event):void
{
// loop through all child element of a movieclip
for (var i: int = 0; i < grid.numChildren; i++)
{
// Cast display objects to Tiles class.
var aTiles:Tiles = grid.getChildAt(i) as Tiles;
// Call the method.
aTiles.getTiles();
}
}