SetNeedsLayout（）导致其他视图不更新

Question

func keyboardWasShown(aNotification: NSNotification)    {
    self.view.setNeedsLayout() /* */

    var info = aNotification.userInfo as NSDictionary

    var kbSize = info.objectForKey(UIKeyboardFrameBeginUserInfoKey).CGRectValue().size

    if self.containerViewController.frame != mainFrame! {
        self.containerViewController.frame = mainFrame!
    }

    var aRect = self.view.frame as CGRect

    aRect.size.height = aRect.size.height - kbSize.height

    if CGRectContainsPoint(aRect, self.textField.frame.origin) == false  {

        self.textField.frame.origin.y = aRect.height - 30
    }
}

为什么self.view.setNeedsLayout（）函数搞砸了textField的位置？它导致textField不移动。布局更新太晚了吗？如果是这样，我该如何解决这个问题。我尝试过self.view.setLayoutIfNeeded（），但这也不起作用。