Basic setup for a test project for debugging lazy loading / saving with NSFileWrappers in a Document based application

gistfile1.m

//
//  Document.m
//  Wrappers
//

#import "Document.h"

#define FileName01 @"testfile1.txt"
#define FileName02 @"testfile2.txt"

@interface Document () {
  
}

@property (nonatomic, retain) NSFileWrapper *myWrapper;
//@property (nonatomic, retain) NSFileWrapper *subDir;

@end

@implementation Document

- (id)init {
    self = [super init];
    if (self) {
    }
    return self;
}

- (NSString *)windowNibName {
	return @"Document";
}

- (void)windowControllerDidLoadNib:(NSWindowController *)aController {
	[super windowControllerDidLoadNib:aController];
}

+ (BOOL)autosavesInPlace {
    return YES;
}

	/**
	 *	Only called when initializing a NEW document
	 */
	-(id)initWithType:(NSString *)typeName error:(NSError *__autoreleasing *)outError {
		self = [self init];
		if (self) {
			self.myWrapper = [[NSFileWrapper alloc] initDirectoryWithFileWrappers:nil];
			
			NSLog(@"Initializing new document...");
			
			NSString *testString1 = @"Lorem ipsum first sub file";
			NSString *testString2 = @"This is the second sub file with completely unrelated contents";
			
			NSFileWrapper *w1 = [[NSFileWrapper alloc] initRegularFileWithContents:[testString1 dataUsingEncoding:NSUTF8StringEncoding]];
			NSFileWrapper *w2 = [[NSFileWrapper alloc] initRegularFileWithContents:[testString2 dataUsingEncoding:NSUTF8StringEncoding]];
			
			w1.preferredFilename = FileName01;
			w2.preferredFilename = FileName02;
			
			[self.myWrapper addFileWrapper:w1];
			[self.myWrapper addFileWrapper:w2];
			
		}
		return self;
	}

	-(NSFileWrapper *)fileWrapperOfType:(NSString *)typeName error:(NSError *__autoreleasing *)outError {
		
		// This obviously wouldn't happen here normally, but it illustrates
		// how the contents of the first file would be replaced
		NSFileWrapper *w1 = [self.myWrapper.fileWrappers objectForKey:FileName01];
		[self.myWrapper removeFileWrapper:w1];
		
		NSFileWrapper *new1 = [[NSFileWrapper alloc] initRegularFileWithContents:[@"New file contents" dataUsingEncoding:NSUTF8StringEncoding]];
		new1.preferredFilename = FileName01;
		
		[self.myWrapper addFileWrapper:new1];
		
		return self.myWrapper;
	}

	-(BOOL)readFromFileWrapper:(NSFileWrapper *)fileWrapper ofType:(NSString *)typeName error:(NSError *__autoreleasing *)outError {
		self.myWrapper = fileWrapper;
		return YES;
	}

	- (IBAction)button1Pressed:(id)sender {
		// Read from file1 and show result in field1
		NSFileWrapper *w1 = [[self.myWrapper fileWrappers] objectForKey:FileName01];
		NSString *string1 = [[NSString alloc] initWithData:w1.regularFileContents encoding:NSUTF8StringEncoding];
		[self.field1 setStringValue:string1];
	}

	- (IBAction)button2Pressed:(id)sender {
		// Read from file2 and show result in field2
		NSFileWrapper *w2 = [[self.myWrapper fileWrappers] objectForKey:FileName02];
		NSString *string2 = [[NSString alloc] initWithData:w2.regularFileContents encoding:NSUTF8StringEncoding];
		[self.field2 setStringValue:string2];
	}

-(BOOL)isEntireFileLoaded {
	return YES;
}

@end