Question

My iPhone game crashed whilst on the device and I am attempting to understand what happened.

Every time a user exits the game screen it will send a message to the HomePageController (my top level controller) telling it to save the user data. This works fine all the time except for in this particular instance. The exception thrown seems to state that HomePageController did not recognize the saveUserData selector but I can’t see how that can happen as that function is definitely in that controller and it works the rest of the time.

Can anyone offer any advice?

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x00000000, 0x00000000
Crashed Thread:  0

Last Exception Backtrace:
0 CoreFoundation      0x3756a88f __exceptionPreprocess + 163
1 libobjc.A.dylib     0x35a70259 objc_exception_throw + 33
2 CoreFoundation      0x3756da9b -[NSObject doesNotRecognizeSelector:] + 175
3 CoreFoundation      0x3756c915 ___forwarding___ + 301
4 CoreFoundation      0x374c7650 _CF_forwarding_prep_0 + 48
5 P------k            0x0000ebe1 -[HomePageController saveUserData] (HomePageController.m:125)
6 P------k            0x00008a0b -[RootViewController viewDidAppear:] (RootViewController.m:102)

Line 125 in HomePageController.m:

- (void)saveUserData{
    NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                                   NSUserDomainMask, YES) objectAtIndex:0];
    //10x10
    {
        NSMutableDictionary *dict = [[[NSMutableDictionary alloc] init] autorelease];
        for (int i = 0; i < _puzzles10x10.count; i++){
            LevelData *currentPuzzle = [_puzzles10x10 objectAtIndex:i];
            /*(line 125)*/ [dict setObject:[currentPuzzle getPuzzleUserData] forKey:currentPuzzle.title];
        }

        [dict writeToFile:[documentsPath stringByAppendingPathComponent:@"userdata.dat"] atomically:YES];
    }
    // more here
}

Answer 1

If currentPuzzle doesn’t recognize the selector getPuzzleUserData then the problem is one of these two:

1. LevelData does not define a method getPuzzleUserData.
2. currentPuzzle is not an instance of LevelData

So check if the method is actually defined in the class LevelData and not in HomePageController and that when you add items to _puzzles10x10 they are actually instances of LevelData.

To debug further, split your code into as many lines as possible (one instruction per line), add a lot of NSLog calls and see what happens:

NSLog(@"_puzzles10x10: %@", _puzzles10x10);
for (int i = 0; i < _puzzles10x10.count; i++){
    LevelData *currentPuzzle = [_puzzles10x10 objectAtIndex:i];
    NSLog(@"currentPuzzle#%d: %@", i, currentPuzzle);
    UserData *userData = [currentPuzzle getPuzzleUserData]; // change UserData to the correct t class
    NSLog(@"userData#%d: %@", i, userData);
    NSString *key = currentPuzzle.title;
    NSLog(@"key#%d: %@", i, key);
    [dict setObject:userData forKey:key];
}