iOS App Clarification for The Verge

Posted by pete42 on October 24, 2012 02:43 pm 1

Yesterday I was watching the Vergecast Live and wanted to clarify a few things that both The Verge staff and Andrew S. Allen from fiftythree didn't understand about iOS app development. The thing that was not understood was about targeting an app for a specific device (i.e. screen size/resolution). Up until the iPhone 5 and now the iPad mini there was no need to target different devices since they all had 3.5 or 9.7 inch screens. The retina devices were just more pixel dense without changing the size of the screen. Andre Allen was right in saying that naming images with the @2x suffix will make the app retina ready but you can actually make completely different apps for retina and non retina.

For example this happens with universal apps since it is one binary that points to different files based on what device is using it. The following piece of code shows how Xcode does this when creating universal app is created.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.


  if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        self.viewController = [[MainViewController alloc] initWithNibName:@"MainViewController_iPhone" bundle:nil];
    } else {
        self.viewController = [[MainViewController alloc] initWithNibName:@"MainViewController_iPad" bundle:nil];
    }


    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

This piece of code (in bold) allows the app to detect if its a phone or not and run the right file when the app launches. We all know that this can be done but what The Verge staff do not know is that the [UIDevice currentDevice] has some other properties that can specify the exact device the developer wants to target. The model attribute of the [UIDevice currentDevice] returns whether the device is an iPad, iPhone or iPod. With this you can target each one individually. But there is also a much more granular way to target devices that require a third party extension for UIDevice made by Erica Sadun which can be found here.

In order to understand how to do this, one must understand how apple identifies its product. For example the first iPhone was iPhone1,1 while the iPhone 5 comes in two variants the iPhone5,1 and iPhone5,2. By simply calling [[UIDevice currentDevice] platform] you will get this model identifier and make an app just for one device. The simplified code looks like this for finding the id:

size_t size;
sysctlbyname("hw.machine", NULL, &size, NULL, 0);

char *answer = malloc(size);

sysctlbyname("hw.machine", answer, &size, NULL, 0);

NSString *results = [NSString stringWithCString:answer encoding: NSUTF8StringEncoding];
//result = iPad3,1 on 3rd generation iPad


free(answer);

With all these tools it is simple to create an iPad Mini or iPhone 5 specific app. The code would look something like the following:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.

    NSString *modelID = [[UIDevice currentDevice] platform];

    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {

 if ([modelID isEqualToString: @"iPhone5,1"] || [modelID isEqualToString: @"iPhone5,2"]) {
             self.viewController = [[MainViewController alloc] initWithNibName:@"MainViewController_iPhone_5" bundle:nil];
        }

        else {
             self.viewController = [[MainViewController alloc] initWithNibName:@"MainViewController_iPhone" bundle:nil];
        }
    }

    else {
 if ([modelID isEqualToString: @"iPad5,1"]) { //the model identifier for the iPad mini is not known yet
            self.viewController = [[MainViewController alloc] initWithNibName:@"MainViewController_iPad_Mini" bundle:nil];
        }

        else {
            self.viewController = [[MainViewController alloc] initWithNibName:@"MainViewController_iPad" bundle:nil];
        }
    }
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

The code in first bold section shows how to set up the app so that if an iPhone 5 runs the app then the app will point to a special iPhone 5 version of the app. The second bolded part shows that if the device has the model identifier for the iPad Mini (not yet know but probably iPad5,1 or iPad4,4) then the app will run the iPad Mini version. The basic flow of the piece of code is that it checks whether the device is a phone (iPod/iPhone) or a tablet (iPad) and then inside that check it checks if the device is an iPhone 5 or iPad Mini. Hopefully this will clear up some confusion about whether or not you can create an iOS app for a specific device. Feel free to leave your questions in the comments if you have any.

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iOS App Clarification for The Verge

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