How to subclass UIApplication?

The iPhone Reference Libary - UIApplication says I can subclass UIApplication, but if I try this I will get an exception:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'There can only be one UIApplication instance.'

This reminds me of the Highlander "There can be only one,. :-)

Do I have to pass other argurments to UIApplicationMain? Or did I missread somthing in the libary?

Solution 1:

Did you pass the name of your subclass to UIApplicationMain? Let's assume you have

@interface MyUIApp : UIApplication 
...

then in main() you should do:

NSString* appClass = @"MyUIApp";
NSString* delegateClass = nil;
int retVal = UIApplicationMain(argc, argv, appClass, delegateClass);

Solution 2:

In your app's info.plist, make sure you change the NSPrincipalClass key to the name of your subclass. This'll make Cocoa instantiate the correct class when the applications loads - you shouldn't have to do anything other than that to get your subclass working.

Solution 3:

I know this is an old one and accepted answer is o.k., but to make it clear...

Let's say you have:

UIApplication subclassed as MyApplication

UIApplicationDelegate subclassed as MyAppDelegate

Then your main.m would look like:

#import <UIKit/UIKit.h>

#import "MyApplication.h"
#import "MyAppDelegate.h"

int main(int argc, char * argv[])
{
    @autoreleasepool
    {
        return UIApplicationMain(argc,
                                 argv,
                                 NSStringFromClass([MyApplication class]),
                                 NSStringFromClass([MyAppDelegate class]));                
    }
}

In case you did not subclass UIApplication or UIApplicationDelegate you simply pass nil to the UIApplicationMain as the respective parameter.