滚动 UICollectionView 以响应键盘通知

Question

我正在构建一个信使应用程序。

我目前的键盘通知功能如下：

func handleKeyboardNotification(notification: NSNotification) {

        if let userInfo = notification.userInfo {
            let keyboardFrame = userInfo[UIKeyboardFrameEndUserInfoKey]?.CGRectValue()
            print(keyboardFrame)


            let isKeyboardShowing = notification.name == UIKeyboardWillShowNotification


            bottomConstraint?.constant = isKeyboardShowing ? -keyboardFrame!.height : 0



            UIView.animateWithDuration(0, delay: 0, options: UIViewAnimationOptions.CurveEaseOut, animations: {

                self.view.layoutIfNeeded()
                }, completion: { (completed) in

                    if isKeyboardShowing {
                        let indexPath = NSIndexPath(forItem: self.messages!.count - 1, inSection: 0)
                        self.collectionView?.scrollToItemAtIndexPath(indexPath, atScrollPosition: .Bottom, animated: true)
                    }

            })

    }
}

（bottomConstraint.constant是指位于屏幕底部或键盘框架顶部的消息输入文本字段）

但是，我希望完成参数中的操作与键盘打开同时发生，而不是在键盘打开之后发生。目前，当我关闭键盘时，它似乎自动布局很好，只是在我打开它时没有。

到目前为止，我已经尝试了很多方法，但均无济于事。 有什么建议吗？

Answer 1

如果您希望在完成中编写的代码块与键盘按下同时发生，那么您不应该在完成块中编写它。 您可以在调用具有持续时间的动画之前使用 dispatch_async 函数，这样它就可以同时工作：

   func handleKeyboardNotification(notification: NSNotification) {

            if let userInfo = notification.userInfo {
                let keyboardFrame = userInfo[UIKeyboardFrameEndUserInfoKey]?.CGRectValue()
                print(keyboardFrame)


                let isKeyboardShowing = notification.name == UIKeyboardWillShowNotification


                bottomConstraint?.constant = isKeyboardShowing ? -keyboardFrame!.height : 0

DispatchQueue.main.async {
    if isKeyboardShowing {
                    let indexPath = NSIndexPath(forItem: self.messages!.count - 1, inSection: 0)
                            self.collectionView?.scrollToItemAtIndexPath(indexPath, atScrollPosition: .Bottom, animated: true)
}


            UIView.animateWithDuration(0, delay: 0, options: UIViewAnimationOptions.CurveEaseOut, animations: {self.view.layoutIfNeeded()}, completion: nil})

    }
}