Question

Using Xcode 4.2, my app runs in iOS 5.0 simulator. It runs on a 3G iPhone with iOS 4.2.1. It does not run on an iPod with iOS 3.1.3.

This is boilerplate code I got from any number of tutorials, but on the iOS 3.1.3 device, after displaying my Default.png, this line fails:

self.window.rootViewController = self.viewController;

with ‘Unrecognized selector sent to instance’ in my ykAppDelegate.m here:

#import "ykAppDelegate.h"
#import "ykViewController.h"

@implementation ykAppDelegate

@synthesize window;
@synthesize viewController;

#pragma mark -
#pragma mark Application lifecycle

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch.

    // Set the view controller as the window's root view controller and display.
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];

    return YES;
}

With a more than cursory glance at the code, I notice viewController isn’t apparently instantiated (except for @synthesize); it’s just declared in my ykAppDelegate.h:

#import <UIKit/UIKit.h>

@class ykViewController;

@interface ykAppDelegate : NSObject <UIApplicationDelegate> {
    UIWindow *window;
    ykViewController *viewController;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet ykViewController *viewController;

@end

Is there a small tweak I can make so this will work in iOS 3.1?

Answer 1

In pre-iOS5 operating systems UIWindow doesn’t have a property named ‘rootViewController’. An idiomatic solution is to simply add the view controller’s view as a subview to your application’s key window:

[window addSubview:self.myViewController.view];