Swift：通过NSNotificationCenter的键盘观察器不起作用

Question

我正在尝试在我的iOS 8 Swift应用程序中实现一个简单的键盘观察器，但它确实不起作用。 这是我目前正在使用的代码：

override func viewDidAppear(animated: Bool) {
    NSNotificationCenter().addObserver(self, selector: Selector(keyboardWillAppear()), name: UIKeyboardWillShowNotification, object: nil)
    NSNotificationCenter().addObserver(self, selector: Selector(keyboardWillHide()), name: UIKeyboardWillHideNotification, object: nil)
}

override func viewDidDisappear(animated: Bool) {
    NSNotificationCenter().removeObserver(self)
}

func keyboardWillAppear() {
    logoHeightConstraint.constant = 128.0
}

func keyboardWillHide() {
    logoHeightConstraint.constant = 256.0
}

奇怪的是，在启动应用程序后，两个对键盘作出反应的功能都会被调用。 当我进入或离开文本字段时没有任何反应。 我究竟做错了什么？ 顺便说一下：改变约束是改变图像大小的最佳解决方案吗？

我真的很感谢你的帮助！

Answer 1

每次调用NSNotificationCenter()调用NSNotificationCenter()都会实例化一个新的NSNotificationCenter 。 请尝试使用NSNotificationCenter.defaultCenter() 。

Answer 2

//keyboard observers 
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillAppear"), name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide"), name: UIKeyboardWillHideNotification, object: nil)




func keyboardWillAppear() {
    println("Keyboard appeared")
}

func keyboardWillHide() {
    println("Keyboard hidden")
}

Answer 3

我更喜欢使用UIKeyboardWillChangeFrameNotification，因为如果大小发生变化，您会收到通知，例如，当隐藏/显示建议时

//keyboard observers 
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(keyboardWillChange), name: UIKeyboardWillChangeFrameNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(keyboardWillHide), name: UIKeyboardWillHideNotification, object: nil)

func keyboardWillChange(notification:NSNotification)
{
    print("Keyboard size changed")
}

func keyboardWillHide(notification:NSNotification)
{
    print("Keyboard hidden")
}

Answer 4

Swift 4.0，闭包😍：

NotificationCenter.default.addObserver(forName: .UIKeyboardDidShow, object: nil, queue: nil, using: { notification in
   // do stuff
})

Answer 5

Swift 3及以上代码。 添加了获取键盘高度的代码

func addObservers() {
    //keyboard observers
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidAppear(notification:)), name: NSNotification.Name.UIKeyboardDidShow, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(notification:)), name: NSNotification.Name.UIKeyboardDidHide, object: nil)
}

@objc func keyboardDidAppear(notification: NSNotification) {
    print("Keyboard appeared")
    let keyboardSize:CGSize = (notification.userInfo![UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue.size
    print("Keyboard size: \(keyboardSize)")

    let height = min(keyboardSize.height, keyboardSize.width)
    let width = max(keyboardSize.height, keyboardSize.width)
    print(height)
    print(width)
}

@objc func keyboardWillHide(notification: NSNotification) {
    print("Keyboard hidden")
}