// 保存原来的亮度
[[NSUserDefaults standardUserDefaults] setObject:@([UIScreen mainScreen].brightness) forKey:@"brightness"];
// 保存状态，需要为用户变化屏幕亮度功能
[[NSUserDefaults standardUserDefaults] setObject:@YES forKey:@"ifNeedChangeLight"];

- (void)viewDidAppear:(BOOL)animated
{
  [super viewDidAppear:animated];
  if ([UIScreen mainScreen].brightness < 0.8) {
    [UIScreen mainScreen].brightness = 0.8;
  }
}

- (void):(BOOL)animated
{
  [super viewDidDisappear:animated];
  // 还原
  [UIScreen mainScreen].brightness = [[[NSUserDefaults standardUserDefaults] objectForKey:@"brightness"] floatValue];
  [[NSUserDefaults standardUserDefaults] setObject:@NO forKey:@"ifNeedChangeLight"];
}

- (void)applicationWillResignActive:(UIApplication *)application {
  if ([[[NSUserDefaults standardUserDefaults] objectForKey:@"ifNeedChangeLight"] boolValue]) {
    [UIScreen mainScreen].brightness = [[[NSUserDefaults standardUserDefaults] objectForKey:@"brightness"] floatValue];
  }
}
- (void)applicationDidBecomeActive:(UIApplication *)application {
  if ([[[NSUserDefaults standardUserDefaults] objectForKey:@"ifNeedChangeLight"] boolValue]) {
    if ([UIScreen mainScreen].brightness < 0.8) {
      // 颜色需要渐变的话需要另外再写
      [UIScreen mainScreen].brightness = 0.8;
    }
  }
}