iOS 通过接受距离传感器的消息改变屏幕的明暗度（仅限用于真实的手机）

 #import "AppDelegate.h"

 @interface AppDelegate ()

 @end

 @implementation AppDelegate

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
     self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
     // Override point for customization after application launch.
     self.window.backgroundColor = [UIColor whiteColor];

     UIDevice *device = [UIDevice currentDevice];
     device.proximityMonitoringEnabled = YES;
     if (device.proximityMonitoringEnabled == YES) {
         [[NSNotificationCenter defaultCenter] addObserver:self
                                                  selector:@selector(proximityChanged:)
                                                      name:@"UIDeviceProximityStateDidChangeNotification" object:device];
     }

     [self.window makeKeyAndVisible];
     return YES;
 }

 - (void)tuneBrightness:(NSTimer *)timer
 {
     if ([UIScreen mainScreen].brightness < ) {
         [UIScreen mainScreen].brightness += 0.05;
     }else{
         [timer invalidate];
     }
 }

 - (void)proximityChanged:(NSNotification *)notification
 {
     UIDevice *device = [notification object];
     if (!device.proximityState) {
         [NSTimer scheduledTimerWithTimeInterval:0.3 target:self selector:@selector(tuneBrightness:) userInfo:nil repeats:YES];
     }
 }

 - (void)applicationWillTerminate:(UIApplication *)application {
     // 删除Observer
     [[NSNotificationCenter defaultCenter] removeObserver:self];

 }

 @end