Blackberry DateField positioning

I'm trying to center my date time on the screen using DateField in Blackberry. My code appears not to function as I expect it to. Can a kind soul divine what the problem might be:

setPositionChild(df, 
    (Display.getWidth()/2-(df.getContentWidth()/2)),
    (Display.getHeight()-df.getC开发者_开发技巧ontentHeight())/2);

If everything fails you can put this date field in a manager and allign it to center of the manager by both vertical and horizontal. After that you can add this field (manager) to the screen.