The slider button on the side of the iPad can, optionally, be used to lock the device’s orientation. This means that if you want the screen to stay in portrait mode, it won’t move when you turn it sideways if locked. However despite the presence of the rotation lock (and unlike the iPhone where many applications only supported Portrait mode) an iPad application is expected to support all orientations equally.

To implement basic support for all interface orientations, you should implement the shouldAutorotateToInterfaceOrientation: method in all of your application’s view controllers, returning YES for all orientations. Additionally, you should configure the auto-resizing mark property of your views inside Interface Builder so that they correctly respond to layout changes (i.e. rotation of the device).

We cover the camera in detail in Chapter 2, however it is simple matter to determine whether a camera is present in the device:

BOOL available = [UIImagePickerController
  isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera];

Once you have determined that a camera is present you can enquire whether it supports video by making a call to determine the available media types the camera supports:

NSArray *media = [UIImagePickerController availableMediaTypesForSourceType:
                  UIImagePickerControllerSourceTypeCamera];

If the kUTTypeMovie media type is returned as part of the array, then the camera will support video recording:

if ( [media containsObject:(NSString *)kUTTypeMovie ] ){
    NSLog(@"Camera supports movie capture.");
}

An initial poll of whether audio input is available can be done using the AVAudioSession class by checking the inputIsAvailable class property:

AVAudioSession *audioSession = [AVAudioSession sharedInstance];
BOOL audioAvailable = audioSession.inputIsAvailable;

#import <AVFoundation/AVFoundation.h>

You can also be notified of any changes in the availability of audio input, e.g., if a second generation iPod touch user has plugged in headphones with microphone capabilities. First, nominate your class as a delegate:

audioSession.delegate = self;

And then declare it as implementing the AVAudioSessionDelegate protocol in the declaration:

@interface YourAppDelegate : NSObject <UIApplicationDelegate,
  AVAudioSessionDelegate >

Then implement the inputIsAvailableChanged: in the implementation:

- (void)inputIsAvailableChanged:(BOOL)audioAvailable {
      NSLog(@"Audio availability has changed");
}

The short answer to a commonly asked question is that the Core Location framework does not provide any way to get direct information about the availability of specific hardware such as the GPS at application run time, although you can check whether location services are enabled:

BOOL locationAvailable = [CLLocationManager locationServicesEnabled];

However, you can require the presence of GPS hardware for your application to load (see ).

Fortunately Core Location does allow you to check for the presence of the magnetometer (digital compass) fairly simply:

BOOL magnetometerAvailable = [[CLLocationManager headingAvailable];

If your application requires a persistent WiFi connection you can set the Boolean UIRequiresPersistentWiFi key in the Application’s Info.plist file to ensure that WiFi is available. If set to YES the operating system will open a WiFi connection when your application is launched and keep it open while the application is running. If this key is not present, or is set to NO, the Operating System will close the active WiFi connection after 30 minutes.

Setting the UIBackgroundModes key in the Application’s Info.plist file notifies the operating systems that the application should continue to run in the background, after the user closes it, since it provides specific background services.

There are three possible key values: audio, location, and voip. The audio key indicates that after closing the application will continue to play audible content. The location key indicates that the application provides location-based information for the user using the standard Core Location services, rather than the newer significant location change service. Finally, the voip key indicates that the application provides Voice-over-IP services. Applications marked with this key are automatically launched after system boot so that the application can attempt to re-establish VoIP services.