Question

I’m working in Xcode 4.3.2.

I’m trying to load a Nib programmatically instead of using Storyboards. Storyboards seems a lot simpler, but unfortunately they are not compatible with iOS 4 & I’m building an application that requires backwards compatibility.

Here’s my problem: I’m trying to load the main view – a simple view with a green background. Currently there is no default view.

My files are:

AppDelegate.h/.m
GreenViewController.h/.m
SwitchViewController.h/.m

I want to the green screen to load when the app begins so in AppDelegate.m I have:

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

    //UIView *switchView = self.switchViewController.view;


    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

In SwitchViewController.m I have:

- (void)viewDidLoad
{
    self.greenViewController = [[GreenViewController alloc] initWithNibName:@"GreenView" bundle:nil];
    [self.view insertSubview:self.greenViewController.view atIndex:0];
    [super viewDidLoad];
}

With the simple initWithNibName filled in with the default code.

In GreenViewController.m I have:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

Here is the main functionality of everything. When I run the app, I immediately get the error:

2012-10-09 12:34:35.586 MyViewSwitcher[5210:f803] -[AppDelegate setSwitchViewController:]: unrecognized selector sent to instance 0x6c6c310
2012-10-09 12:34:35.587 MyViewSwitcher[5210:f803] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[AppDelegate setSwitchViewController:]: unrecognized selector sent to instance 0x6c6c310'

Can someone please help me understand the cause of my error? I made sure the the “Custom Class” of the GreenView.xib is the “GreenViewController” in the Identity Inspector. Also, I made sure that the referencing outlet for “View” was the file’s owner. I want to load the GreenView nib when my app launches. Eventually, I will switch views by adding a button, but so far I haven’t been able to even load the main view. I’m not sure what I’m misunderstanding.

Thank you in advance for you help!

Answer 1

The problem is not with loading the nib. The problem is on this line:

self.switchViewController = [[SwitchViewController alloc] initWithNibName:@"GreenView" bundle:nil];

Here you are using “dot syntax“, which is explained in The Objective-C Programming Language. When you set a property using that syntax, the compiler transforms it into a regular Objective-C message like this:

[self setSwitchViewController:[[SwitchViewController alloc] initWithNibName:@"GreenView" bundle:nil]];

At runtime, the system is telling you that your AppDelegate object doesn’t understand the setSwitchViewController: method. You need to use an @synthesize directive, which is explained in The Objective-C Programming Language, to tell the compiler to implement the setSwitchViewController: method for you:

@synthesize switchViewController = _switchViewController;