在macOS的程序开发中，经常需要知道系统一些状态的改变而去对程序 做出一定的处理！比如收到系统睡眠、唤醒、切换用户、屏幕关闭、显示屏保等系统状态。

• 大部分的系统状态，通过“NSWorkspace .shared .notificationCenter”来实现：

NSWorkspace .shared .notificationCenter .addObserver(self, selector: #selector(methodWillSleepNotification), name: NSWorkspace.willSleepNotification, object: nil)
NSWorkspace .shared .notificationCenter .addObserver(self, selector: #selector(methodDidWakeNotification), name: NSWorkspace.didWakeNotification, object: nil)
NSWorkspace .shared .notificationCenter .addObserver(self, selector: #selector(methodScreensDidSleepNotification), name: NSWorkspace.screensDidSleepNotification, object: nil)
NSWorkspace .shared .notificationCenter .addObserver(self, selector: #selector(methodScreensDidWakeNotification), name: NSWorkspace.screensDidWakeNotification, object: nil)
NSWorkspace .shared .notificationCenter .addObserver(self, selector: #selector(methodWillPowerOffNotification), name: NSWorkspace.willPowerOffNotification, object: nil)
NSWorkspace .shared .notificationCenter .addObserver(self, selector: #selector(methodSessionDidResignActiveNotification), name: NSWorkspace.sessionDidResignActiveNotification, object: nil)
NSWorkspace .shared .notificationCenter .addObserver(self, selector: #selector(methodSessionDidBecomeActiveNotification), name: NSWorkspace.sessionDidBecomeActiveNotification, object: nil)

相应的响应方法：

//睡眠                //NSWorkspace.willSleepNotification
@objc func methodWillSleepNotification () {
    print("methodWillSleepNotification")
}
//从睡眠中唤醒        //NSWorkspace.didWakeNotification
@objc func methodDidWakeNotification () {
    print("methodDidWakeNotification")
}
//屏幕睡眠          //NSWorkspace.screensDidSleepNotification
@objc func methodScreensDidSleepNotification () {
    print("methodScreensDidSleepNotification")
}
//屏幕唤醒          //NSWorkspace.screensDidWakeNotification
@objc func methodScreensDidWakeNotification () {
    print("methodScreensDidWakeNotification")
}
//当用户注销或关机      //NSWorkspace.willPowerOffNotification
@objc func methodWillPowerOffNotification () {
    print("methodWillPowerOffNotification")
}
//被切换到另一用户      //NSWorkspace.sessionDidResignActiveNotification
@objc func methodSessionDidResignActiveNotification () {
    print("methodSessionDidResignActiveNotification")
}
//被切换回到当前用户     //NSWorkspace.sessionDidBecomeActiveNotification
@objc func methodSessionDidBecomeActiveNotification () {
    print("methodSessionDidBecomeActiveNotification")
}

• 对于某一些特殊系统状态(如‘屏保’/‘锁定屏幕’等)，就需要NSDistributedNotificationCenter(跨进程的通知)来实现：

//对于某一些系统状态，就需要以下的DistributedNotificationCenter(跨进程的通知)来实现：
DistributedNotificationCenter .default() .addObserver(self, selector: #selector(method_screenSaverDidStart), name: NSNotification.Name(rawValue: "com.apple.screensaver.didstart"), object: nil)
DistributedNotificationCenter .default() .addObserver(self, selector: #selector(method_screenSaverWillStop), name: NSNotification.Name(rawValue: "com.apple.screensaver.willstop"), object: nil)
DistributedNotificationCenter .default() .addObserver(self, selector: #selector(method_screenSaverDidStop), name: NSNotification.Name(rawValue: "com.apple.screensaver.didstop"), object: nil)
DistributedNotificationCenter .default() .addObserver(self, selector: #selector(method_screenIsLocked), name: NSNotification.Name(rawValue: "com.apple.screenIsLocked"), object: nil)
DistributedNotificationCenter .default() .addObserver(self, selector: #selector(method_screenIsUnlocked), name: NSNotification.Name(rawValue: "com.apple.screenIsUnlocked"), object: nil)

相应的响应方法：

//屏保开始      //"com.apple.screensaver.didstart"
@objc func method_screenSaverDidStart() {
    print("method_screenSaverDidStart")
}
//屏保将要结束    //"com.apple.screensaver.willstop"
@objc func method_screenSaverWillStop() {
    print("method_screenSaverWillStop")
}
//屏保结束      //"com.apple.screensaver.didstop"
@objc func method_screenSaverDidStop() {
    print("method_screenSaverDidStop")
}
//屏幕锁住      //"com.apple.screenIsLocked"
@objc func method_screenIsLocked() {
    print("method_screenIsLocked")
}
//屏幕解锁      //"com.apple.screenIsUnlocked"
@objc func method_screenIsUnlocked() {
    print("method_screenIsUnlocked")
}

书写好上面的代码后，开始模拟情景测试~

• A.直接选择屏幕顶部菜单栏对应的'睡眠'项：

打印如下：

methodWillSleepNotification
methodScreensDidSleepNotification
method_screenIsLocked
method_screenIsUnlocked
methodDidWakeNotification
methodScreensDidWakeNotification

其中，点击'睡眠'项后进行睡眠的打印：

methodWillSleepNotification
methodScreensDidSleepNotification
method_screenIsLocked

重新唤醒后的打印：

method_screenIsUnlocked
methodDidWakeNotification
methodScreensDidWakeNotification

• B.直接选择顶部菜单栏对应的'锁定屏幕'项：

打印如下：

method_screenIsLocked
method_screenIsUnlocked

其中，点击'锁定屏幕'项后进行锁屏的打印：

method_screenIsLocked

重新输入该账户密码，解锁屏幕后的打印：

method_screenIsUnlocked

'系统偏好设置'里面的'桌面与屏幕保护程序'和'节能'

• C.启动'屏幕保护程序'：需要选择相应的闲置时长

启动'屏幕保护程序'，需要选择相应的闲置时间

• • C-1.自动弹出了屏幕保护，但是系统还未进入休眠：
  • • • 【一】、在系统偏好设置的'节能'中设置为'永不'—永远不进行休眠
        
        当前'节能'中设置的时长为‘永不’
  • • • 【二】、在系统偏好设置的'节能'中设置相应的放置时长—可以进行休眠
        
        当前'节能'中设置的时长为‘1分钟’

【一】、在系统偏好设置的'节能'中设置为'永不'——不管是 (已经被锁屏)需要输入用户解锁屏幕的密码、(还没有被锁屏)还不需要输入用户解锁屏幕的密码！
【二】、在系统偏好设置的'节能'中设置为‘1分钟’——只是出现了屏幕保护(系统还未休眠)就激活电脑来退出了屏幕保护！
上面的情况【一】、【二】，打印都如下：

method_screenSaverDidStart
method_screenIsLocked
method_screenSaverWillStop
method_screenSaverDidStop
method_screenIsUnlocked

其中，自动弹出了屏幕保护的打印：

method_screenSaverDidStart
method_screenIsLocked

解锁屏幕后的打印：（不管是否需要重新输入该账户密码）

method_screenSaverWillStop
method_screenSaverDidStop
method_screenIsUnlocked

• • C-2.自动弹出了屏幕保护，并再放置到系统睡眠（系统偏好设置的'节能'中，设置相应的放置时长）

当前'节能'中设置的时长为‘1分钟’

[$-1].不需要重新输入该账户密码：

method_screenSaverDidStart
method_screenIsLocked
methodScreensDidSleepNotification
method_screenSaverWillStop
method_screenSaverDidStop
method_screenSaverWillStop
method_screenSaverDidStop
method_screenIsUnlocked
methodScreensDidWakeNotification

[$-2].需要重新输入该账户密码：

method_screenSaverDidStart
method_screenIsLocked
methodScreensDidSleepNotification
method_screenSaverWillStop
method_screenSaverDidStop
method_screenSaverWillStop
method_screenSaverDidStop
methodScreensDidWakeNotification
method_screenIsUnlocked

其中，自动弹出了屏幕保护，并再放置到系统睡眠

method_screenSaverDidStart
method_screenIsLocked
methodScreensDidSleepNotification

解锁屏幕后的打印：

• [$-1].不需要重新输入该账户密码

method_screenSaverWillStop
method_screenSaverDidStop
method_screenSaverWillStop
method_screenSaverDidStop
method_screenIsUnlocked
methodScreensDidWakeNotification

• [$-2].需要重新输入该账户密码

method_screenSaverWillStop
method_screenSaverDidStop
method_screenSaverWillStop
method_screenSaverDidStop
methodScreensDidWakeNotification
method_screenIsUnlocked

更多系统状态相应响应方法的顺序——根据你自己开发App的需求，就自己试出其调用顺序再搭配使用吧~

OC代码：

[[[NSWorkspace sharedWorkspace] notificationCenter] addObserver:self selector:@selector(sleepMethod:) name:NSWorkspaceWillSleepNotification object:nil];

//其中能捕获到的状态有：
//NSWorkspaceWillSleepNotification  //睡眠
//NSWorkspaceDidWakeNotification  //从睡眠中唤醒
//NSWorkspaceWillPowerOffNotification  //当用户注销或关机
//NSWorkspaceSessionDidResignActiveNotification  //被切换到另一用户
//NSWorkspaceSessionDidBecomeActiveNotification  //被切换回到当前用户
//NSWorkspaceScreensDidSleepNotification  //屏幕睡眠
//NSWorkspaceScreensDidWakeNotification  //屏幕唤醒  

需要去实现其响应方法(sleepMethod:)~

对于某一些系统状态(如‘屏保’/‘锁定屏幕’等)，就需要NSDistributedNotificationCenter(跨进程的通知)来实现：

[[NSDistributedNotificationCenter defaultCenter] addObserver:self selector:@selector(screensaverStart:) name:@"com.apple.screensaver.didstart" object:nil];

//其中的通知名称可以是：
//com.apple.screensaver.didstart  //屏保开始
//com.apple.screensaver.willstop  //屏保将要结束
//com.apple.screensaver.didstop  //屏保结束
//com.apple.screenIsLocked  //屏幕锁住
//com.apple.screenIsUnlocked  //屏幕解锁

同样需要去实现其响应方法(screensaverStart:)~

以上便是关于macOS系统状态的讨论~
关于NSApp对应的App状态讨论，请参考《NSApp — App状态及其通知》！

goyohol's essay