Basic Sensors in iOS

Determining Device Orientation

Apple provide an easy way of determining the device orientation, a call to UIDevice will return the current orientation of the device:

UIDevice *device = [UIDevice currentDevice];
UIDeviceOrientation orientation = device.orientation;

This call will return a UIDeviceOrientation that can be: UIDeviceOrientationUnknown, UIDeviceOrientationPortrait, UIDeviceOrientationPortraitUpsideDown, UIDeviceOrientationLandscapeLeft, UIDeviceOrientationLandscapeRight or UIDeviceOrientationFaceUp. The sensor underlying this call is the accelerometer, and you’ll see later in this chapter how to retrieve the device orientation directly from the raw accelerometer readings.

Warning

As of the time of writing under iOS 4.3 the device does not correctly report a proper orientation when your application is first launched, with UIDevice returning null when queried.

Lets go ahead and modify the Accelerometer application to display the device orientation. Click on the AccelerometerViewController.h interface file to open it in the Standard Editor and add the following code, highlighted below, to the class interface:

@interface AccelerometerViewController : 
      UIViewController <UIAccelerometerDelegate> {

    IBOutlet UILabel *xLabel;
    IBOutlet UILabel *yLabel;
    IBOutlet UILabel *zLabel;

    IBOutlet UIProgressView *xBar;
    IBOutlet UIProgressView *yBar;
    IBOutlet UIProgressView *zBar;
    IBOutlet UILabel *orientationLabel;

    UIAccelerometer *accelerometer;
}

- (NSString *)stringFromOrientation:(UIDeviceOrientation) ...