应用程序的单例类对象中得到应用程序委托的对象
UIApplicationDelegate* myDelegate = [[UIApplication sharedApplication] delegate];
UIApplication 接收到所有的系统事件和生命周期事件时，都会把事件传递给UIApplicationDelegate进行处理，对于用户输入事件，则传递给相应的目标对象去处理。
- (void)applicationWillResignActive:(UIApplication *)application
通知委托应用程序将进入非活动状态，在此期间，应用程序不接收消息或事件。
这个方法在用户锁住屏幕时，也会调用。
与之相适应的是应用程序重新被用户打开时的委托 方法。另外常用的就是内存不足的系统警告，此时会调用应用程序委托类的applicationDidReceiveMemoryWarning()方法， 然后我们就可以试着释放一些内存了。
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), NULL, updateEnabled, CFSTR("com.apple.iokit.hid.displayStatus"), NULL, CFNotificationSuspensionBehaviorDeliverImmediately);
// 1状态
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), NULL, lockComplete, CFSTR("com.apple.springboard.lockcomplete"), NULL, CFNotificationSuspensionBehaviorDeliverImmediately);
// 2状态
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), NULL, lockState, CFSTR("com.apple.springboard.lockstate"), NULL, CFNotificationSuspensionBehaviorDeliverImmediately);
static void updateEnabled(CFNotificationCenterRef center, void* observer, CFStringRef name, const void* object, CFDictionaryRef userInfo) {
uint64_t state;
int token;
notify_register_check("com.apple.iokit.hid.displayStatus", &token);
notify_get_state(token, &state);
notify_cancel(token);
NSLog(@"锁屏状态：%llu",state);
}
static void lockComplete(CFNotificationCenterRef center, void* observer, CFStringRef name, const void* object, CFDictionaryRef userInfo) {
uint64_t state;
int token;
notify_register_check("com.apple.springboard.lockcomplete", &token);
notify_get_state(token, &state);
notify_cancel(token);
NSLog(@"lockComplete状态：%llu",state);
}
static void lockState(CFNotificationCenterRef center, void* observer, CFStringRef name, const void* object, CFDictionaryRef userInfo) {
uint64_t state;
int token;
notify_register_check("com.apple.springboard.lockstate", &token);
notify_get_state(token, &state);
notify_cancel(token);
NSLog(@"lockState状态：%llu",state);
}