Add core data to an existing project in xcode 4

Adding core data to an existing project is not much different in Xcode 4. Just the model editor has changed a bit, here’s a tutorial showing the steps.

1.) Right click on Supporting Files and select New File.

2.) Choose iOS > Core Data > Data Model and click Next

3.) Name the file and click Save

4.) A new file will show up under Supporting Files

5.) Select it and the core data model editor will open up

6.) Click the Add Entity button

And name the Entity

7.) Click the Add Attribute button

Name the attribute and set it’s type

8.) Select the Album entity

9.) Select File > New File from the menu bar

Choose Core Data > NSManagedObject subclass and hit Next

10.) Click Create on the next screen, I just use the default location.

11.) Add an import to the -prefix.pch file so you don’t have to import Core Data whenever you need it

#import 

#ifndef __IPHONE_3_0
#warning "This project uses features only available in iPhone SDK 3.0 and later."
#endif

#ifdef __OBJC__
    #import 
    #import 
    #import 
#endif

12.) Declare private variables for NSManagedObjectContext, NSManagedObjectModel and NSPersistentStoreCoordinator in the app delegate header file.

#import 
#import "EnterViewController.h"

@interface CoreDataTestAppDelegate : NSObject 
{

    EnterViewController *enterViewController;

@private
    NSManagedObjectContext *managedObjectContext;
    NSManagedObjectModel *managedObjectModel;
    NSPersistentStoreCoordinator *persistentStoreCoordinator;

}

@property (nonatomic, retain) IBOutlet UIWindow *window;

@property (nonatomic, retain) IBOutlet UITabBarController *tabBarController;

@property (nonatomic, retain) IBOutlet EnterViewController *enterViewController;

@property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;

- (NSURL *)applicationDocumentsDirectory;
- (void)saveContext;

@end

13.) Implement the actions you declared in the header file, in the app delegate implementation file.

/**
 Returns the URL to the application's Documents directory.
 */
- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

- (void)saveContext
{

    NSError *error = nil;
    NSManagedObjectContext *objectContext = self.managedObjectContext;
    if (objectContext != nil)
    {
        if ([objectContext hasChanges] && ![objectContext save:&error])
        {
            // add error handling here
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}

14.) Implement the necessary core data methods in the app delegate implementation file

#pragma mark -
#pragma mark Core Data stack

/**
 Returns the managed object context for the application.
 If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
 */
- (NSManagedObjectContext *)managedObjectContext
{

    if (managedObjectContext != nil)
    {
        return managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil)
    {
        managedObjectContext = [[NSManagedObjectContext alloc] init];
        [managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return managedObjectContext;
}

/**
 Returns the managed object model for the application.
 If the model doesn't already exist, it is created from the application's model.
 */
- (NSManagedObjectModel *)managedObjectModel
{
    if (managedObjectModel != nil)
    {
        return managedObjectModel;
    }
    managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];

    return managedObjectModel;
}

/**
 Returns the persistent store coordinator for the application.
 If the coordinator doesn't already exist, it is created and the application's store added to it.
 */
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{

    if (persistentStoreCoordinator != nil)
    {
        return persistentStoreCoordinator;
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"CoreDataTabBarTutorial.sqlite"];

    NSError *error = nil;
    persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error])
    {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }  

    return persistentStoreCoordinator;
}

15.) Core data is now ready to go. You’ll still need to get the managedObjectContext to which ever view controller you want to use it in and then implement the save or retrieve processes.