Xcode 3.x to 4.2 transition - Runs once then stuck

Question

I am teaching myself Xcode from a good book.  However I ran into a strange thing where a code example runs once in Xcode 4.2 and after that builds clean but gets in a loop when running and never even brings up the screen I set up in XIB.  It doesn't matter if I change the code or not.  The message showing in the debugger is [Switching to process 5521 thread 0x0] - the number seems to be rather random.  The first run was clearly stopped using the menu quit command, but it is like it is trying to write over itself or something.
It finally dawned on me that perhaps this has something to do with the upgrade from Xcode 3.x to Xcode 4.2.  The book example I am following was written to Xcode 3.  The book examples had similar errors with NSDictionary and NSArray examples.
The code is pretty short, so I am including it all.  It really is beginner level.  I am sure I just need an experienced eye to point out some mis-direction on my part.  Thanks for any coaching I can get.  I only wrote the first method and added a line to the init method. 
Document.h
#import <Cocoa/Cocoa.h>
@interface Document : NSDocument
    NSMutableDictionary *mainDictionary;
    IBOutlet NSTextField *kRefInField;
    IBOutlet NSTextField *dataInField;
- (IBAction)storeRefAndData: (id)sender;
@end
Document.m
#import "Document.h"
@implementation Document
- (IBAction)storeRefAndData: (id)sender
    NSString *kRefToStore = [kRefInField stringValue];
    NSString *dataToStore = [dataInField stringValue];
    [mainDictionary setValue:dataToStore forKey:kRefToStore];
- (id)init
    self = [super init];
    if (self) {
        // Add your subclass-specific initialization here.
        // If an error occurs here, return nil.
        mainDictionary = [[NSMutableDictionary alloc] init];
    return self;
- (NSString *)windowNibName
    // Override returning the nib file name of the document
    // If you need to use a subclass of NSWindowController or if your document supports multiple NSWindowControllers, you should remove this method and override -makeWindowControllers instead.
    return @"Document";
- (void)windowControllerDidLoadNib:(NSWindowController *)aController
    [super windowControllerDidLoadNib:aController];
    // Add any code here that needs to be executed once the windowController has loaded the document's window.
- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError
     Insert code here to write your document to data of the specified type. If outError != NULL, ensure that you create and set an appropriate error when returning nil.
    You can also choose to override -fileWrapperOfType:error:, -writeToURL:ofType:error:, or -writeToURL:ofType:forSaveOperation:originalContentsURL:error: instead.
    NSException *exception = [NSException exceptionWithName:@"UnimplementedMethod" reason:[NSString stringWithFormat:@"%@ is unimplemented",NSStringFromSelector(_cmd)]userInfo:nil];
    @throw exception;
    return nil;
- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName error:(NSError**)outError
    Insert code here to read your document from the given data of the specified type. If outError != NULL, ensure that you create and set an appropriate error when returning NO.
    You can also choose to override -readFromFileWrapper:ofType:error: or -readFromURL:ofType:error: instead.
    If you override either of these, you should also override -isEntireFileLoaded to return NO if the contents are lazily loaded.
    NSException *exception = [NSException exceptionWithName:@"UnimplementedMethod" reason:[NSString stringWithFormat:@"%@ is unimplemented",NSStringFromSelector(_cmd)]userInfo:nil];
    @throw exception;
    return YES;
+ (BOOL)autosavesInPlace
    return YES;
@end

Answer 1

I am teaching myself Xcode from a good book.  However I ran into a strange thing where a code example runs once in Xcode 4.2 and after that builds clean but gets in a loop when running and never even brings up the screen I set up in XIB.  It doesn't matter if I change the code or not.  The message showing in the debugger is [Switching to process 5521 thread 0x0] - the number seems to be rather random.  The first run was clearly stopped using the menu quit command, but it is like it is trying to write over itself or something.
It finally dawned on me that perhaps this has something to do with the upgrade from Xcode 3.x to Xcode 4.2.  The book example I am following was written to Xcode 3.  The book examples had similar errors with NSDictionary and NSArray examples.
The code is pretty short, so I am including it all.  It really is beginner level.  I am sure I just need an experienced eye to point out some mis-direction on my part.  Thanks for any coaching I can get.  I only wrote the first method and added a line to the init method. 
Document.h
#import <Cocoa/Cocoa.h>
@interface Document : NSDocument
    NSMutableDictionary *mainDictionary;
    IBOutlet NSTextField *kRefInField;
    IBOutlet NSTextField *dataInField;
- (IBAction)storeRefAndData: (id)sender;
@end
Document.m
#import "Document.h"
@implementation Document
- (IBAction)storeRefAndData: (id)sender
    NSString *kRefToStore = [kRefInField stringValue];
    NSString *dataToStore = [dataInField stringValue];
    [mainDictionary setValue:dataToStore forKey:kRefToStore];
- (id)init
    self = [super init];
    if (self) {
        // Add your subclass-specific initialization here.
        // If an error occurs here, return nil.
        mainDictionary = [[NSMutableDictionary alloc] init];
    return self;
- (NSString *)windowNibName
    // Override returning the nib file name of the document
    // If you need to use a subclass of NSWindowController or if your document supports multiple NSWindowControllers, you should remove this method and override -makeWindowControllers instead.
    return @"Document";
- (void)windowControllerDidLoadNib:(NSWindowController *)aController
    [super windowControllerDidLoadNib:aController];
    // Add any code here that needs to be executed once the windowController has loaded the document's window.
- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError
     Insert code here to write your document to data of the specified type. If outError != NULL, ensure that you create and set an appropriate error when returning nil.
    You can also choose to override -fileWrapperOfType:error:, -writeToURL:ofType:error:, or -writeToURL:ofType:forSaveOperation:originalContentsURL:error: instead.
    NSException *exception = [NSException exceptionWithName:@"UnimplementedMethod" reason:[NSString stringWithFormat:@"%@ is unimplemented",NSStringFromSelector(_cmd)]userInfo:nil];
    @throw exception;
    return nil;
- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName error:(NSError**)outError
    Insert code here to read your document from the given data of the specified type. If outError != NULL, ensure that you create and set an appropriate error when returning NO.
    You can also choose to override -readFromFileWrapper:ofType:error: or -readFromURL:ofType:error: instead.
    If you override either of these, you should also override -isEntireFileLoaded to return NO if the contents are lazily loaded.
    NSException *exception = [NSException exceptionWithName:@"UnimplementedMethod" reason:[NSString stringWithFormat:@"%@ is unimplemented",NSStringFromSelector(_cmd)]userInfo:nil];
    @throw exception;
    return YES;
+ (BOOL)autosavesInPlace
    return YES;
@end