iOS-UI - 假夜间模式-VC 屏幕遮住

/******* 假夜间模式 *********/

// 开关
UISwitch *sw = [[UISwitch alloc] initWithFrame:CGRectMake(100, 200, 100, 100)];
[sw addTarget:self action:@selector(swAction:) forControlEvents:UIControlEventValueChanged];
[self.view addSubview:sw];
[sw release];

• (void)swAction:(UISwitch *)sender
  {
  if (YES == sender.on) {

  // 假夜间模式
  self.nightV = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
  self.nightV.backgroundColor = [UIColor blackColor];
  self.nightV.alpha = 0.6;
  self.nightV.userInteractionEnabled = NO;
  [self.view addSubview:self.nightV];
  [self.nightV release];
  

  } else {

  // 关闭夜间模式 移除视图
  
  [self.nightV removeFromSuperview];

  }
  }