使用Orientation Changed Notification遇到的问题及解决办法

有些情况下uiviewcontroller自带的rotate方法会不起作用，所以需要使用uidevice的Orientation Changed Notification方法

Orientation Changed Notification使用方法：

Orientation Changed Notification

Add to #AppDelegate.m didFinishLaunchingWithOptions

	//----- SETUP DEVICE ORIENTATION CHANGE NOTIFICATION -----
	UIDevice *device = [UIDevice currentDevice];					//Get the device object
	[device beginGeneratingDeviceOrientationNotifications];			//Tell it to start monitoring the accelerometer for orientation
	NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];	//Get the notification centre for the app
	[nc addObserver:self											//Add yourself as an observer
		   selector:@selector(orientationChanged:)
			   name:UIDeviceOrientationDidChangeNotification
			 object:device];

Function To Receive Notification Message

//********** ORIENTATION CHANGED **********
- (void)orientationChanged:(NSNotification *)note
{
	NSLog(@"Orientation  has changed: %d", [[note object] orientation]);
}

不过这样会有个问题，那就是UIDeviceOrientation是有6种，而UIInterfaceOrientation是4种，这样在使用 UIDeviceOrientationIsPortrait的时候如果取反就会包含unknown或者faceup等情况

typedef enum {
   UIDeviceOrientationUnknown,
   UIDeviceOrientationPortrait,
   UIDeviceOrientationPortraitUpsideDown,
   UIDeviceOrientationLandscapeLeft,
   UIDeviceOrientationLandscapeRight,
   UIDeviceOrientationFaceUp,
   UIDeviceOrientationFaceDown
} UIDeviceOrientation;

解决方法：在 orientationChanged:(NSNotification *)note中加入如下代码：

if ([[note object] orientation] == UIDeviceOrientationUnknown ||

        [[note object] orientation] == UIDeviceOrientationFaceUp  ||

        [[note object] orientation] == UIDeviceOrientationFaceDown) return;

这样就可以放心使用 UIDeviceOrientationIsPortrait了