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