Question

I have a preference that, when set, forces my application to perform some synchronization on startup.

Can I use IB to display a different initial view based on this setting?

Is there a standard way to enable this behavior?

Answer 1

Assuming you have a property on your app delegate that is set during your synchronization, in the initial view controller’s initWithNibNamed: method check the value synced by the app delegate and load the appropriate nib by calling [super initWithNibNamed:@"thisNibInsteadOfThatNib"];

EDIT: Show code to launch a different view depending on some condition at launch

// AppDelegate.h
#import <UIKit/UIKit.h>

@interface AppDelegate : NSObject <UIApplicationDelegate>
{
    UIWindow *window;
    UIViewController *firstViewController;
}
@property {nonatomic, retain} UIWindow *window;
@end

// AppDelegate.m
#import AppDelegate.h
#import ViewControllerOne.h
#import ViewControllerTwo.h

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    BOOL shouldLoadViewOne = \\ some value from preferences

    if (shouldLoadViewOne) {
        firstViewController = [[ViewOneController alloc] initWithNibName:@"ViewOneController" bundle:nil];
    } else {
        firstViewController = [[ViewTwoController alloc] initWithNibName:@"ViewTwoController" bundle:nil];
    }

    UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:firstViewController];

    [window addSubView:[navController view]];

    [window makeKeyAndVisible];

    return YES;
}

EDIT 2:

Make use of NSClassFromSting() and save the name of the firstViewController to load in the preferences.

// AppDelegate.h
#import <UIKit/UIKit.h>

@interface AppDelegate : NSObject <UIApplicationDelegate>
{
    UIWindow *window;
    id firstViewController;
}
@property {nonatomic, retain} UIWindow *window;

- (NSString *)firstViewControllerName;

@end

// AppDelegate.m
#import AppDelegate.h
#import ViewControllerOne.h
#import ViewControllerTwo.h

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    NSString *viewControllerName = [self firstViewControllerName];

    firstViewController = [[NSClassFromString(viewControllerName) alloc] initWithNibName:viewControllerName  bundle:nil];

    UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:firstViewController];

    [window addSubView:[navController view]];

    [window makeKeyAndVisible];

    return YES;
}

- (NSString *)firstViewControllerName
{
    NSString *defaultViewController = @"ViewOneController";
    NSString *savedFirstViewController = // string retrieved from preferences or other persistent store

    if (!savedFirstViewController)
        return defaultViewController;

    return savedFirstViewController;
}