内容简介：Swift iOS : NotificationCenter
类NotificationCenter提供了一种轻耦合的消息传递机制。可以发起一个通知，在多处监听此通知。比如说一个App的主题样式被修改，就可以通过此类来通知多个相关UI，做响应的处理。
如下案例展示了这种可能：
import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
self.window = UIWindow();
self.window?.frame=UIScreen.main.bounds;
self.window?.makeKeyAndVisible();
NotificationCenter.default.addObserver(self, selector: #selector(themeChange), name: Notification.Name("themeChange"), object: nil)
self.window?.rootViewController = Page()
return true
}
func themeChange(){
print("themeChange2")
}
}
class Page: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .blue
NotificationCenter.default.addObserver(self, selector: #selector(themeChange), name: Notification.Name("themeChange"), object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(themeChange1), name: Notification.Name("themeChange"), object: nil)
NotificationCenter.default.post(name: Notification.Name("themeChange"), object: nil)
}
func themeChange(){
print("themeChange")
}
func themeChange1(){
print("themeChange1")
}
}
执行此代码，输出应该是：
themeChange2 themeChange themeChange1
通过 NotificationCenter.default.addObserver在类Page1做了两处对“themeChange”通知的监听，在类AppDelegate做了一处对此通知的监听。然后当：
NotificationCenter.default.post(name: Notification.Name("themeChange"), object: nil)
执行时，三处监听函数都会被调用。
NotificationCenter还可以监听系统通知，比如App进入前景和背景，按如下方法监听即可：
import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
self.window = UIWindow();
self.window?.frame=UIScreen.main.bounds;
self.window?.makeKeyAndVisible();
self.window?.rootViewController = Page()
return true
}
}
class Page: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .blue
NotificationCenter.default.addObserver(self, selector: #selector(applicationWillEnterForeground), name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(applicationDidEnterBackground), name: NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
}
func applicationWillEnterForeground(){
print("applicationWillEnterForeground")
}
func applicationDidEnterBackground(){
print("applicationDidEnterBackground")
}
}
应用执行后，按HOME按钮，可以看到输出：
applicationDidEnterBackground
再度执行App可以看到输出：
applicationWillEnterForeground
以上所述就是小编给大家介绍的《Swift iOS : NotificationCenter》，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对 码农网 的支持！
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