Actionscript 3 MovieClip包含TextField，但跟踪为null

我正试着把一些电影剪辑到一个物体上

var br1_txt:TextField = new TextField();
br1_txt.text = "t";
br1_txt.defaultTextFormat = tfB;
br1_txt.setTextFormat(tfB);
br1_txt.textColor = 0x000000;
br1_txt.x = -3;
br1_txt.y = -3;

var br1_mc:MovieClip = new MovieClip();
br1_mc.addChild(br1_txt);
addChild(br1_mc);

var array:Array = new Array();

var object1:Object = new Object;
var s1:MovieClip = this.getChildByName("squared2") as MovieClip;
var piece1:MovieClip = this.getChildByName("br1_mc") as MovieClip;
object1.s1 = s1; // or object["movieClip"] = movieClip
object1.piece1 = piece1;
array.push(object1);
trace(s1); // Outputs [object MovieClip]
trace(piece1); // Outputs null, why?

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问题在于：this.getChildByName（“br1_-mc”）br1_-mc是一个变量名，而不是实例名。插入此br1_mc.name=“br1_mc”；在创建br1\u mc之后的某个地方，在调用this.getChildByName（“br1\u mc”）之前