iOS通知中心
它是iOS程序内部的一种消息广播机制，通过它，可以实现无引用关系的对象之间的通信。通知中心他是基于观察者模式，它只能进行程序内部通信，不能跨应用程序进程通信。
当通知中心接受到消息后会根据设置，将消息发送给订阅者，这里的订阅者可以有多个
通知中心原理
看完上图你应该明白通知中心所做的事情了吧, 接下来我们就来看看通知中心。
首先必须了解2个类:
// 这个类用来传递发送通知过程中传递信息的载体 NSNotification // 这是iOS中通知中心的灵魂, 由该类实现了观察者模式, 并给开发者提供了诸如注册、删除观察者的接口, 我们可以通过一个单例来获得它的实例 NSNotificationCenter
代码实现
注册一个通知观察者
// 注册一个通知观察者 NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.refreshText(_:)), name: kRefreshTextNotification, object: nil) self: 观察者 selector: 收到通知执行的方法 name: 通知名 object: // 收到通知后执行的方法 func refreshText(notification: NSNotification) { if notification.object is NSError { return } textField.text = String(notification.object!) }
向观察者发送通知
NSNotificationCenter.defaultCenter().postNotificationName(kRefreshTextNotification, object: "fffffff", userInfo: nil) kRefreshTextNotification: 通知名 object: 参数 userInfo: 其他参数
移除观察者
deinit { NSNotificationCenter.defaultCenter().removeObserver(self, name: kRefreshTextNotification, object: nil) }
除了上面这种方式系统还有一个
NSNotificationCenter.defaultCenter().addObserverForName(kRefreshTextNotification, object: self, queue: NSOperationQueue.mainQueue()) { (notification) in}
但是在项目中并不多用, 所以就不详细介绍了,其实用法差不多, 只不过用的时候需要注意循环引用问题, 比如你在内部用self, 这个self对应的class对象就不会被释放
移除观察者需要注意 不能用 NSNotificationCenter.defaultCenter().removeObserver(self, name: kRefreshTextNotification, object: nil), 需要用 NSNotificationCenter.defaultCenter().removeObserver(observer)
系统通知
除了自定义的通知名, 系统其实还有一部分通知名
UIDevice通知
UIDeviceOrientationDidChangeNotification // 设备旋转 UIDeviceBatteryStateDidChangeNotification // 电池状态改变 UIDeviceBatteryLevelDidChangeNotification // 电池电量改变 UIDeviceProximityStateDidChangeNotification // 近距离传感器(比如设备贴近了使用者的脸部)
键盘通知
UIKeyboardWillShowNotification // 键盘即将显示 UIKeyboardDidShowNotification // 键盘显示完毕 UIKeyboardWillHideNotification // 键盘即将隐藏 UIKeyboardDidHideNotification // 键盘隐藏完毕 UIKeyboardWillChangeFrameNotification // 键盘的位置尺寸即将发生改变 UIKeyboardDidChangeFrameNotification // 键盘的位置尺寸改变完毕
系统发出键盘通知时, 会附带一下跟键盘有关的额外信息(字典),字典常见的key如下:
UIKeyboardFrameBeginUserInfoKey // 键盘刚开始的frame UIKeyboardFrameEndUserInfoKey // 键盘最终的frame(动画执行完毕后) UIKeyboardAnimationDurationUserInfoKey // 键盘动画的时间 UIKeyboardAnimationCurveUserInfoKey // 键盘动画的执行节奏(快慢)
app通知
// These notifications are sent out after the equivalent delegate message is called @available(iOS 4.0, *) public let UIApplicationDidEnterBackgroundNotification: String @available(iOS 4.0, *) public let UIApplicationWillEnterForegroundNotification: String public let UIApplicationDidFinishLaunchingNotification: String public let UIApplicationDidBecomeActiveNotification: String public let UIApplicationWillResignActiveNotification: String public let UIApplicationDidReceiveMemoryWarningNotification: String public let UIApplicationWillTerminateNotification: String public let UIApplicationSignificantTimeChangeNotification: String public let UIApplicationWillChangeStatusBarOrientationNotification: String // userInfo contains NSNumber with new orientation public let UIApplicationDidChangeStatusBarOrientationNotification: String // userInfo contains NSNumber with old orientation public let UIApplicationStatusBarOrientationUserInfoKey: String // userInfo dictionary key for status bar orientation public let UIApplicationWillChangeStatusBarFrameNotification: String // userInfo contains NSValue with new frame public let UIApplicationDidChangeStatusBarFrameNotification: String // userInfo contains NSValue with old frame public let UIApplicationStatusBarFrameUserInfoKey: String // userInfo dictionary key for status bar frame @available(iOS 7.0, *) public let UIApplicationBackgroundRefreshStatusDidChangeNotification: String @available(iOS 3.0, *) public let UIApplicationLaunchOptionsURLKey: String // userInfo contains NSURL with launch URL @available(iOS 3.0, *) public let UIApplicationLaunchOptionsSourceApplicationKey: String // userInfo contains NSString with launch app bundle ID @available(iOS 3.0, *) public let UIApplicationLaunchOptionsRemoteNotificationKey: String // userInfo contains NSDictionary with payload @available(iOS 4.0, *) public let UIApplicationLaunchOptionsLocalNotificationKey: String // userInfo contains a UILocalNotification @available(iOS 3.2, *) public let UIApplicationLaunchOptionsAnnotationKey: String // userInfo contains object with annotation property list @available(iOS 4.0, *) public let UIApplicationProtectedDataWillBecomeUnavailable: String @available(iOS 4.0, *) public let UIApplicationProtectedDataDidBecomeAvailable: String @available(iOS 4.0, *) public let UIApplicationLaunchOptionsLocationKey: String // app was launched in response to a CoreLocation event. @available(iOS 5.0, *) public let UIApplicationLaunchOptionsNewsstandDownloadsKey: String // userInfo contains an NSArray of NKAssetDownload identifiers @available(iOS 7.0, *) public let UIApplicationLaunchOptionsBluetoothCentralsKey: String // userInfo contains an NSArray of CBCentralManager restore identifiers @available(iOS 7.0, *) public let UIApplicationLaunchOptionsBluetoothPeripheralsKey: String // userInfo contains an NSArray of CBPeripheralManager restore identifiers @available(iOS 9.0, *) public let UIApplicationLaunchOptionsShortcutItemKey: String // userInfo contains the UIApplicationShortcutItem used to launch the app. // Key in options dict passed to application:[will | did]FinishLaunchingWithOptions and info for UIApplicationDidFinishLaunchingNotification @available(iOS 8.0, *) public let UIApplicationLaunchOptionsUserActivityDictionaryKey: String // Sub-Dictionary present in launch options when user activity is present @available(iOS 8.0, *) public let UIApplicationLaunchOptionsUserActivityTypeKey: String // Key in user activity dictionary for the activity type @available(iOS 8.0, *) public let UIApplicationOpenSettingsURLString: String // Keys for application:openURL:options: @available(iOS 9.0, *) public let UIApplicationOpenURLOptionsSourceApplicationKey: String // value is an NSString containing the bundle ID of the originating application @available(iOS 9.0, *) public let UIApplicationOpenURLOptionsAnnotationKey: String // value is a property-list typed object corresponding to what the originating application passed in UIDocumentInteractionController's annotation property @available(iOS 9.0, *) public let UIApplicationOpenURLOptionsOpenInPlaceKey: String // value is a bool NSNumber, set to YES if the file needs to be copied before use // Content size category constants @available(iOS 7.0, *) public let UIContentSizeCategoryExtraSmall: String @available(iOS 7.0, *) public let UIContentSizeCategorySmall: String @available(iOS 7.0, *) public let UIContentSizeCategoryMedium: String @available(iOS 7.0, *) public let UIContentSizeCategoryLarge: String @available(iOS 7.0, *) public let UIContentSizeCategoryExtraLarge: String @available(iOS 7.0, *) public let UIContentSizeCategoryExtraExtraLarge: String @available(iOS 7.0, *) public let UIContentSizeCategoryExtraExtraExtraLarge: String // Accessibility sizes @available(iOS 7.0, *) public let UIContentSizeCategoryAccessibilityMedium: String @available(iOS 7.0, *) public let UIContentSizeCategoryAccessibilityLarge: String @available(iOS 7.0, *) public let UIContentSizeCategoryAccessibilityExtraLarge: String @available(iOS 7.0, *) public let UIContentSizeCategoryAccessibilityExtraExtraLarge: String @available(iOS 7.0, *) public let UIContentSizeCategoryAccessibilityExtraExtraExtraLarge: String // Notification is emitted when the user has changed the preferredContentSizeCategory for the system @available(iOS 7.0, *) public let UIContentSizeCategoryDidChangeNotification: String // userInfo dictionary will contain new value for UIContentSizeCategoryNewValueKey @available(iOS 7.0, *) public let UIContentSizeCategoryNewValueKey: String // NSString instance with new content size category in userInfo // This notification is posted after the user takes a screenshot (for example by pressing both the home and lock screen buttons) @available(iOS 7.0, *) public let UIApplicationUserDidTakeScreenshotNotification: String // Extension point identifier constants @available(iOS 8.0, *) public let UIApplicationKeyboardExtensionPointIdentifier: String