Ios 更新帧时，UITextView跳到屏幕底部，位于键盘后面

我正在实现一个UITextView textInput，其效果与iOS消息窗口类似，其中textview根据文本内容展开/收缩

当我在textViewDidChange函数中更新UITextView框架时，UITextView跳到屏幕底部，隐藏在键盘后面。它不会出现在指定的帧中

这是我的密码

 func textViewDidChange(textView: UITextView)
{
    print ("textview did changed")

    let fixedWidth : CGFloat = textView.frame.size.width
    let newSize : CGSize = textView.sizeThatFits(CGSizeMake(fixedWidth, CGFloat(MAXFLOAT)))
    var newFrame : CGRect = textView.frame
    newFrame.size = CGSizeMake(CGFloat(fmaxf((Float)(newSize.width), (Float)(fixedWidth))),newSize.height)
    textView.frame = newFrame       
}

另外，这里还有keyboardWillAppear（）和keyboardWillAppear（）函数，它们工作正常

func keyboardWillAppear(notification: NSNotification){

    print ("keyboard will appear")

    let userInfo:NSDictionary = notification.userInfo!
    let keyboardSize:CGSize = userInfo.objectForKey(UIKeyboardFrameBeginUserInfoKey)!.CGRectValue().size

    let contentInsets:UIEdgeInsets = UIEdgeInsetsMake(0, 0, keyboardSize.height, 0)

    self.tableView.contentInset = contentInsets
    self.tableView.scrollIndicatorInsets = contentInsets
    scrollToBottomOfTheTable()

    var messageFrame:CGRect = self.textInput.frame
    messageFrame.origin.y -= keyboardSize.height
    self.textInput.frame = messageFrame
}

func keyboardWillDisappear(notification: NSNotification) {

    print ("keyboard will disappear")

    let userInfo:NSDictionary = notification.userInfo!
    let keyboardSize:CGSize = userInfo.objectForKey(UIKeyboardFrameBeginUserInfoKey)!.CGRectValue().size

    UIView.beginAnimations(nil, context: nil)
    UIView.setAnimationDuration(0.25)
    self.tableView.contentInset = UIEdgeInsetsZero
    UIView.commitAnimations()

    self.tableView.scrollIndicatorInsets = UIEdgeInsetsZero

    var messageFrame:CGRect = self.textInput.frame
    messageFrame.origin.y += keyboardSize.height
    self.textInput.frame = messageFrame
}

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请帮忙！谢谢。

您正在使用自动布局吗？不，我没有。没有xib文件，我正在swift文件中构建所有ui元素。