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Registering Your Application

Signing an application with a push-compatible mobile provision is just the first step to working with push notifications. The application must request to register itself with the iPhone's remote notification system. You do this with a single UIApplication call, as follows. The application did finish launching delegate method provides a particularly convenient place to call this.

[[UIApplication sharedApplication]
    registerForRemoteNotificationTypes:types];

This call tells the iPhone OS that your application wants to accept push messages. The types you pass specify what kinds of alerts your application will receive. The iPhone offers three types of notifications:

  • UIRemoteNotificationTypeBadgeThis kind of notification adds a red badge to your application icon on SpringBoard.
  • UIRemoteNotificationTypeSoundSound notifications let you play sound files from your application bundle.
  • UIRemoteNotificationTypeAlertThis style displays a text alert box in SpringBoard or any other application with a custom message using the alert notification.

Choose the types you want to use and or them together. They are bit flags, which combine to tell the notification registration process how you want to proceed. For example, the following flags allow alerts and badges but not sounds.

types = UIRemoteNotificationTypeBadge | UIRemoteNotificationTypeAlert;

Performing the registration updates user settings. As Figure 16-6 shows, a Notifications pane gets added to Settings if one has not already been created by another program. Your application appears as a subpane, offering user control over notification types. Switches appear only for those notifications that you registered. If your application uses just two types, then two switches appear in that pane. Figure 16-6 shows an application that has registered for all three.

Figure 16-6

Figure 16-6 Remote notification controls appear for each application that has registered with the iPhone for push support. These controls are removed when applications unregister.

To remove your application from active participation in push notifications, send unregisterForRemoteNotifications. This unregisters your application for all notification types and does not take any arguments.

[[UIApplication sharedApplication] unregisterForRemoteNotifications];

Retrieving the Device Token

Your application cannot receive push messages until it generates and delivers a device token to your server. It must send that device token to the offsite service that pushes the actual notifications. Recipe 16-1, which follows this section, does not implement server functionality. It provides only the client software.

Recipe 16-1. Push Client Skeleton

#define TEXTVIEWTAG    11

NSString *pushStatus ()
{
    return [[UIApplication sharedApplication]
        enabledRemoteNotificationTypes] ?
        @"Remote notifications were active for this application" :
        @"Remote notifications were not active for this application";
}

@implementation TestBedController

// Fetch the current switch settings
- (NSUInteger) switchSettings
{
    NSUInteger which = 0;
    if ([(UISwitch *)[self.view viewWithTag:101] isOn])
        which = which | UIRemoteNotificationTypeBadge;
    if ([(UISwitch *)[self.view viewWithTag:102] isOn])
        which = which | UIRemoteNotificationTypeAlert;
    if ([(UISwitch *)[self.view viewWithTag:103] isOn])
        which = which | UIRemoteNotificationTypeSound;
    return which;
}

// Change the switches to match reality
- (void) updateSwitches
{
    NSUInteger rntypes = [[UIApplication sharedApplication]
        enabledRemoteNotificationTypes];
    [(UISwitch *)[self.view viewWithTag:101] setOn:
        (rntypes & UIRemoteNotificationTypeBadge)];
    [(UISwitch *)[self.view viewWithTag:102] setOn:
        (rntypes & UIRemoteNotificationTypeAlert)];
    [(UISwitch *)[self.view viewWithTag:103] setOn:
        (rntypes & UIRemoteNotificationTypeSound)];
}

// Little hack work-around to catch the end when the
// confirmation dialog goes away. Apple has given this
// the thumbs up for use after I filed a technical query
- (void) confirmationWasHidden: (NSNotification *) notification
{
    [[UIApplication sharedApplication]
        registerForRemoteNotificationTypes: [self switchSettings]];
    [self updateSwitches];
}

// Register application for the services set out by the switches
- (void) doOn
{
    UITextView *tv = (UITextView *)[self.view viewWithTag:TEXTVIEWTAG];
    if (![self switchSettings])
    {
        tv.text = [NSString stringWithFormat:
            @"%@\nNothing to register. Skipping.\n            (Did you mean to press Unregister instead?)",
            pushStatus()];
        [self updateSwitches];
        return;
    }

    NSString *status = [NSString stringWithFormat:
        @"%@\nAttempting registration", pushStatus()];
    tv.text = status;
    [[UIApplication sharedApplication]
         registerForRemoteNotificationTypes:[self switchSettings]];
}

// Unregister application for all push notifications
- (void) doOff
{
    UITextView *tv = (UITextView *)[self.view viewWithTag:TEXTVIEWTAG];
    NSString *status = [NSString stringWithFormat:
        @"%@\nUnregistering.", pushStatus()];
    tv.text = status;

    [[UIApplication sharedApplication]
        unregisterForRemoteNotifications];
    [self updateSwitches];
}

- (void)loadView
{
    self.view = [[[NSBundle mainBundle] loadNibNamed:@"view" owner:self
        options:NULL] objectAtIndex:0];
    self.title = @"Push Client";

    self.navigationItem.rightBarButtonItem = BARBUTTON(@"Register",
        @selector(doOn);
    self.navigationItem.leftBarButtonItem = BARBUTTON(@"Unregister",
        @selector(doOff);
    [self updateSwitches];
    [[NSNotificationCenter defaultCenter] addObserver:self
        selector:@selector(confirmationWasHidden)
        name:@"UIApplicationDidBecomeActiveNotification" object:nil];
}
@end
@interface SampleAppDelegate : NSObject <UIApplicationDelegate>
@end

@implementation SampleAppDelegate
- (void) showString: (NSString *) aString
{
    UITextView *tv = (UITextView *)[[[UIApplication sharedApplication]
        keyWindow] viewWithTag:TEXTVIEWTAG];
    tv.text = aString;
}

// Retrieve the device token
- (void)application:(UIApplication *)application
        didRegisterForRemoteNotificationsWithDeviceToken:
           (NSData *)deviceToken
{
    NSUInteger rntypes = [[UIApplication sharedApplication]
       enabledRemoteNotificationTypes];
    NSString *results = [NSString stringWithFormat:
        @"Badge: %@, Alert:%@, Sound: %@",
        (rntypes & UIRemoteNotificationTypeBadge) ? @"Yes" : @"No",
        (rntypes & UIRemoteNotificationTypeAlert) ? @"Yes" : @"No",
        (rntypes & UIRemoteNotificationTypeSound) ? @"Yes" : @"No"];

    NSString *status = [NSString stringWithFormat:
        @"%@\nRegistration succeeded.\n\nDevice Token: %@\n%@",
        pushStatus(), deviceToken, results];
    [self showString:status];
    NSLog(@"deviceToken %@", deviceToken);
}

// Provide a user explanation for when the registration fails
- (void)application:(UIApplication *)application
       didFailToRegisterForRemoteNotificationsWithError:
          (NSError *)error
{

    NSString *status = [NSString stringWithFormat:
        @"%@\nRegistration failed.\n\nError: %@", pushStatus(),
        [error localizedDescription]];
    [self showString:status];
    NSLog(@"Error in registration. Error: %@", error);
}

// Handle an actual notification
- (void)application:(UIApplication *)application
        didReceiveRemoteNotification:(NSDictionary *)userInfo
{
    NSString *status = [NSString stringWithFormat:
        @"Notification received:\n%@",[userInfo description]];
    [self showString:status];
    CFShow([userInfo description]);
}

// Report the notification payload when launched by alert
- (void) launchNotification: (NSNotification *) notification
{

    [self performSelector:@selector(showString)
        withObject:[[notification userInfo] description]
        afterDelay:1.0f];
}

- (void)applicationDidFinishLaunching:(UIApplication *)application {
    UIWindow *window = [[UIWindow alloc]
        initWithFrame:[[UIScreen mainScreen] bounds]];
    UINavigationController *nav = [[UINavigationController alloc]
        initWithRootViewController:[[TestBedController alloc] init]];
    [window addSubview:nav.view];
    [window makeKeyAndVisible];

    // Listen for remote notification launches
    [[NSNotificationCenter defaultCenter] addObserver:self
        selector:@selector(launchNotification)
        name:@"UIApplicationDidFinishLaunchingNotification"
        object:nil];
}
@end

A token is tied to one device. In combination with the SSL certificate, it uniquely identifies the iPhone and can be used to send messages back to the phone in question. Be aware that device tokens can change after you restore iPhone firmware.

Device tokens are created as a byproduct of registration. Upon receiving a registration request, the iPhone OS contacts the Apple Push Notification Service. It uses a secure socket layer (SSL) request. Somewhat obviously, the unit must be connected to the Internet. If it is not, the request will fail. The iPhone forwards the request to APNS and waits for it to respond with a device token.

APNS builds the device token and returns it to the iPhone OS, which in turn passes it back to the application via an application delegate callback, namely

application:didRegisterForRemoteNotificationsWithDeviceToken:

Your application must retrieve this token and pass it to the provider component of your service, where it needs to be stored securely. Anyone who gains access to a device token and the application's SSL certificate could spam messages to iPhones. You must treat this information as sensitive and protect it accordingly.

Handling Token Request Errors

At times, APNS is unable to create a token or your device may not be able to send a request. For example, you cannot generate tokens from the simulator. A UIApplicationDelegate method application: didFailToRegisterForRemote NotificationsWithError: lets you handle these token request errors. For the most part, you'll want to retrieve the error and display it to the user.

// Provide a user explanation for when the registration fails
- (void)application:(UIApplication *)application
    didFailToRegisterForRemoteNotificationsWithError:(NSError *)error
{
    UITextView *tv = (UITextView *)[[application keyWindow]
        viewWithTag:TEXTVIEWTAG];
    NSString *status = [NSString stringWithFormat:
        @"%@\nRegistration failed.\n\nError: %@", pushStatus(),
        [error localizedDescription]];
    tv.text = status;
}

Responding to Notifications

The iPhone uses a set chain of operations (see Figure 16-7) in responding to push notifications. When an application is running, the notification is sent directly to a UIApplicationDelegate method, application: didReceiveRemoteNotification:. The payload, which is sent in JSON format, is converted automatically into an NSDictionary, and the application is free to use the information in that payload however it wants. As the application is already running, no further sounds, badges, or alerts are invoked.

Figure 16-7

Figure 16-7 Visible and audible notification are only presented when the application is not running. Should the user click on an alert's action key (normally View), the application launches and the payload is sent as a notification to the UIApplicationDelegate.

// Handle an actual notification
- (void)application:(UIApplication *)application
    didReceiveRemoteNotification:(NSDictionary *)userInfo
{
    UITextView *tv = (UITextView *)[[application keyWindow]
        viewWithTag:TEXTVIEWTAG];
    NSString *status = [NSString stringWithFormat:
        @"Notification received:\n%@",[userInfo description]];
    tv.text = status;
    NSLog(@"%
}

When an application is not running, the iPhone performs all requested notifications that are allowed by registration and by user settings. These notifications may include playing a sound, badging the application, and/or displaying an alert. Playing a sound can also trigger iPhone vibration when a notification is received.

In the case of an alert, all two-buttoned alerts offer a pair of choices. The user can tap Close (the leftmost button) and close the alert or tap the alert's action key (the rightmost button) and launch the app. Upon launching, the application delegate receives the same remote notification callback that an already-running application would have seen (see Figure 16-8). Alerts appear on the lock screen when the iPhone is locked.

Figure 16-8

Figure 16-8 Remote alerts can appear in SpringBoard (left) or in third-party applications (right). Users may Close the alert or, by pressing the action button on the right, switch to the notifying application. In this case, that application is HelloWorld, whose name is clearly seen on the alert. The action button text is customizable.

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