原文  http://www.cnblogs.com/smileEvday/p/iOS8.html

1、UIWindow的bounds

iOS 7之前Window的bounds不会随着方向而变化，但是到了iOS 8以后，随着设备方向的旋转，window.bounds.size.width和window.bounds.size.height也会相应发生变化。

做个很简单的测试，代码如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  // Override point for customization after application launch.

  [[NSNotificationCenter defaultCenter] addObserver:self
                       selector:@selector(orientationChanged:)
                         name:UIDeviceOrientationDidChangeNotification
                         object:nil];

  return YES;
}

- (void)orientationChanged:(NSNotification*)noti {

  UIDeviceOrientation orientation = [UIDevice currentDevice].orientation;
  NSString *orientationDes = nil;
  switch (orientation) {
    case UIDeviceOrientationLandscapeLeft:
      orientationDes = @"UIInterfaceOrientationLandscapeRight";
      break;
    case UIDeviceOrientationLandscapeRight:
      orientationDes = @"UIInterfaceOrientationLandscapeLeft";
      break;
    case UIDeviceOrientationPortrait:
      orientationDes = @"UIInterfaceOrientationPortrait";
      break;
    case UIDeviceOrientationPortraitUpsideDown:
      orientationDes = @"UIInterfaceOrientationPortraitUpsideDown";
      break;
    default:
      orientationDes = @"";
      break;
  }

  NSLog(@"system ver: %@, \rorientaion: %@, \rwindow bounds: %@",
      [UIDevice currentDevice].systemVersion,
      orientationDes,
      NSStringFromCGRect(self.window.bounds));
}

示例代码很简单，新建一个工程，然后在delegate中直接添加以上代码即可。

iOS 8上运行结果为：

2014-06-04 09:26:32.016 SviOS8[4143:61114] system ver: 8.0,
orientaion: UIInterfaceOrientationLandscapeRight,
window bounds: {{0, 0}, {320, 480}}
2014-06-04 09:26:34.788 SviOS8[4143:61114] system ver: 8.0,
orientaion: UIInterfaceOrientationPortrait,
window bounds: {{0, 0}, {480, 320}}
2014-06-04 09:26:35.791 SviOS8[4143:61114] system ver: 8.0,
orientaion: UIInterfaceOrientationLandscapeLeft,
window bounds: {{0, 0}, {320, 480}}
2014-06-04 09:26:47.468 SviOS8[4143:61114] system ver: 8.0,
orientaion: UIInterfaceOrientationPortraitUpsideDown,
window bounds: {{0, 0}, {480, 320}}

iOS 7及之前的版本运行结果为：

2014-06-04 09:39:00.527 SviOS8[4380:70b] system ver: 7.0.3,
orientaion: UIInterfaceOrientationLandscapeRight,
window bounds: {{0, 0}, {320, 480}}
2014-06-04 09:39:00.895 SviOS8[4380:70b] system ver: 7.0.3,
orientaion: UIInterfaceOrientationPortrait,
window bounds: {{0, 0}, {320, 480}}
2014-06-04 09:39:01.225 SviOS8[4380:70b] system ver: 7.0.3,
orientaion: UIInterfaceOrientationLandscapeLeft,
window bounds: {{0, 0}, {320, 480}}
2014-06-04 09:39:11.004 SviOS8[4380:70b] system ver: 7.0.3,
orientaion: UIInterfaceOrientationPortraitUpsideDown,
window bounds: {{0, 0}, {320, 480}}

通过对比我们可以清晰的看到iOS 8中UIWindow在处理旋转时策略的变更，虽然会因为与之前的版本不同导致现有项目布局存在的bug，但是可以看到iOS 8中的处理方式更加符合我们的预期，在竖向的时候我们就获取到width < height, 在横向则是 width > height，这个符合所见即所得的原则。