Creates a new SimpleButton instance.
Any or all of the display objects that represent the various button states can be set as parameters in the constructor.
Source
SimpleButton([this.upState, this.overState, this.downState, this.hitTestState]) {
this.useHandCursor = true;
this.onMouseOver.listen(_onMouseEvent);
this.onMouseOut.listen(_onMouseEvent);
this.onMouseDown.listen(_onMouseEvent);
this.onMouseUp.listen(_onMouseEvent);
this.onTouchOver.listen(_onTouchEvent);
this.onTouchOut.listen(_onTouchEvent);
this.onTouchBegin.listen(_onTouchEvent);
this.onTouchEnd.listen(_onTouchEvent);
}