如何在默认的通知中心中添加一个观察者?我试图移植这行代码,当电池电量变化时发送通知。
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(batteryLevelChanged:) name:UIDeviceBatteryLevelDidChangeNotification object:nil];
如何在默认的通知中心中添加一个观察者?我试图移植这行代码,当电池电量变化时发送通知。
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(batteryLevelChanged:) name:UIDeviceBatteryLevelDidChangeNotification object:nil];
当前回答
它与Objective-C API相同,但使用了Swift的语法。
Swift 4.2和Swift 5:
NotificationCenter.default.addObserver(
self,
selector: #selector(self.batteryLevelChanged),
name: UIDevice.batteryLevelDidChangeNotification,
object: nil)
如果你的观察者没有从Objective-C对象继承,你必须用@objc作为你的方法的前缀来使用它作为选择器。
@objc private func batteryLevelChanged(notification: NSNotification){
//do stuff using the userInfo property of the notification object
}
参见NSNotificationCenter类参考,与Objective-C api交互
其他回答
NSNotificationCenter在iOS 11的Swift 4.0中添加了观察者语法
NotificationCenter.default.addObserver(self, selector: #selector(keyboardShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
这是为keyboardWillShow通知名称类型。其他类型可以从可用选项中选择
选择器的类型是@objc func,它处理键盘的显示方式(这是你的用户函数)
在swift 2.2 - XCode 7.3中,我们为NSNotificationCenter使用#选择器
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(rotate), name: UIDeviceOrientationDidChangeNotification, object: nil)
使用NSNotificationCenter传递数据
也支持通过swift 3.0中的NotificationCentre和swift 2.0中的NSNotificationCenter进行数据传递。
Swift 2.0版本
使用userInfo传递信息,userInfo是一个可选的字典类型[NSObject: AnyObject]?
let imageDataDict:[String: UIImage] = ["image": image]
// Post a notification
NSNotificationCenter.defaultCenter().postNotificationName(notificationName, object: nil, userInfo: imageDataDict)
// Register to receive notification in your class
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: notificationName, object: nil)
// handle notification
func showSpinningWheel(notification: NSNotification) {
if let image = notification.userInfo?["image"] as? UIImage {
// do something with your image
}
}
Swift 3.0版本
userInfo现在需要[AnyHashable:Any]?作为一个参数,我们在Swift中作为字典字面量提供
let imageDataDict:[String: UIImage] = ["image": image]
// post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict)
// `default` is now a property, not a method call
// Register to receive notification in your class
NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)
// handle notification
func showSpinningWheel(_ notification: NSNotification) {
if let image = notification.userInfo?["image"] as? UIImage {
// do something with your image
}
}
使用NotificationCentre(swift 3.0)和NSNotificationCenter(swift 2.0)传递源数据
它与Objective-C API相同,但使用了Swift的语法。
Swift 4.2和Swift 5:
NotificationCenter.default.addObserver(
self,
selector: #selector(self.batteryLevelChanged),
name: UIDevice.batteryLevelDidChangeNotification,
object: nil)
如果你的观察者没有从Objective-C对象继承,你必须用@objc作为你的方法的前缀来使用它作为选择器。
@objc private func batteryLevelChanged(notification: NSNotification){
//do stuff using the userInfo property of the notification object
}
参见NSNotificationCenter类参考,与Objective-C api交互
Swift 5通知观察员
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(batteryLevelChanged), name: UIDevice.batteryLevelDidChangeNotification, object: nil)
}
@objc func batteryLevelChanged(notification : NSNotification){
//do here code
}
override func viewWillDisappear(_ animated: Bool) {
NotificationCenter.default.removeObserver(self, name: UIDevice.batteryLevelDidChangeNotification, object: nil)
}