Ios 将文本字段移到键盘上方

我一直在实现文档中给出的代码，用于将UIView（如文本字段）推到键盘上方以使其可见-我理解并成功地实现了代码，但我只是对特定函数中的某些行感到困惑。谁能给我解释一下吗？我已经评论了我对编码的看法。如果我错了，请纠正我

func keyboardWasShown(notification: NSNotification)
    {
        //Need to calculate keyboard exact size due to Apple suggestions
        self.scrollView.scrollEnabled = true//enable the scrol view
        let info : NSDictionary = notification.userInfo!//get the userinfo for height of the keyboard
        let keyboardSize = (info[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.CGRectValue().size//get the keyboard height
        let contentInsets : UIEdgeInsets = UIEdgeInsetsMake(0.0, 0.0, keyboardSize!.height, 0.0)

        self.scrollView.contentInset = contentInsets//adjusts the bottom content inset of the scroll view by the height of the keyboard , contentInset - The distance that the content view is inset from the enclosing scroll view.

        self.scrollView.scrollIndicatorInsets = contentInsets//scrollIndicatorInsets - The distance the scroll indicators are inset from the edge of the scroll view.

        var aRect : CGRect = self.view.frame
        aRect.size.height -= keyboardSize!.height
        if let activeFieldPresent = activeField//check for the textfield that is active
        {
            if (!CGRectContainsPoint(aRect, activeField!.frame.origin))
            {
                self.scrollView.scrollRectToVisible(activeField!.frame, animated: true)
            }
        }


    }

现在我的问题是这部分代码中发生了什么-

var aRect : CGRect = self.view.frame
            aRect.size.height -= keyboardSize!.height
            if let activeFieldPresent = activeField//check for the textfield that is active
            {
                if (!CGRectContainsPoint(aRect, activeField!.frame.origin))
                {
                    self.scrollView.scrollRectToVisible(activeField!.frame, animated: true)
                }
            }

---

请逐行解释一下。谢谢你的回答，我会很有帮助。

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