Drag And Drop - droptarget

programming flash
1

Hi, im new with AS, i dont know what im doing wron , i want to make flash drag a ball onpress and if its onrelease and if its on the Suquare movieclip it should stop draggin.

my code is like this

dynamic class Ball extends MovieClip
{

function onPress()
{
    var x_pos = this._x;
    var y_pos = this._y;
    startDrag(this.Ball);
}


function onRelease()
{
    if (this._droptarget == "_root.Square")
    {
        stopDrag();
    }else {
        x_pos = 20;
        y_pos = 20;
    }
        
}

}

can someone help me out plz.

greets