How to center textfield inside MovieClip (AS3) - actionscript-3

Question

I'm having strange problems with positioning of
1) a MovieClip() I've created with AS
2) a textfield inside this MovieClip().
Problem with 1): When I set MC.x = 0; MC.y = 0 the movieClip doesn't appear in the top left corner.
Problem with 2): The text isn't centered vertically nor horizontally.
My AS3 code:
var button:ButtonMC = new ButtonMC();
button.y = 100;
button.x = 100;
button.width = 260;
button.height = 50;
button.buttonMode = true;
button.useHandCursor = true;
button.mouseChildren = false;
var tf:TextFormat = new TextFormat();
tf.size = 70;
tf.bold = true;
tf.font = "Arial"
tf.color = 0xFFFFFF;
var myText:TextField = new TextField();
myText.defaultTextFormat = tf;
myText.autoSize = TextFieldAutoSize.CENTER;
button.addChild(myText);
myText.text = 'ThisIsATestText1234';
myText.y = button.height * 0.5 - myText.textHeight * 0.5;
addChild(button);

Answer 1

Since myText is already added to the button at the point where you try to get the height of the button it might screw up the calculation. Try to align the textfield first and the add it to the button.
You are also changing the width and height of the Button which changes the scale and therefor also affects how the textfield inside looks like and behaves (since it will become a child of the button)
Best way to tackle both problems at once is to create a background-clip within the button and give that the proper size. Then create the textfield and adjust it's scale according to the background. This way the button remains it original scale and won't mess up the stuff that's inside it.
Hope this helps.
PS: useHandCursor = true is not needed when you set buttonMode = true ;)

Answer 2

remove those lines:
button.width = 260;
button.height = 50;
and you will have easier to position text - also the buttons height is affected by added textfield so better use fixed value e.g.
myText.y = 25 - (myText.height * 0.5);