将Core Data添加到现有Xcode项目时未声明的标识符错误

Question

I have an existing project and I want to use CoreData.

Upon creation of the project, the CoreData.framework is already added under my Frameworks group, and it is under Link Binary With Libraries in my project's Target -> Build Phases. I didn't check "Use Core Data" when I created this project-- the check box was not even there --it was just simply in my project. I use Xcode version 4.6.3.

Reading the tutorials, I went to my App-Prefix.pch and added an import to CoreData. It now looks like this:

#import <Availability.h>

#ifndef __IPHONE_5_0
#warning "This project uses features only available in iOS SDK 5.0 and later."
#endif

#ifdef __OBJC__
    #import <UIKit/UIKit.h>
    #import <CoreData/CoreData.h>
    #import <Foundation/Foundation.h>
#endif

Then, I added the following in my AppDelegate.h :

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

- (void)saveContext;

And now, when I override the getter for managedObjectContext , Xcode throws an error:

Use of undeclared identifier '_managedObjectContext'; did you mean 'NSManagedObjectContext'?

This is my getter method in AppDelegate.m :

- (NSManagedObjectContext *)managedObjectContext {
    if(_managedObjectContext != nil)
        return _managedObjectContext;

    NSPersistentStoreCoordinator* psc = [self persistentStoreCoordinator];

    if(psc != nil)
    {
        _managedObjectContext = [[NSManagedObjectContext alloc] init];
        [_managedObjectContext setPersistentStoreCoordinator:psc];
    }

    return _managedObjectContext;
}

I also tried putting the .pch file in my Copy Bundle Resources but to no avail. Help?

Answer 1

You've set everything up correctly (note that you don't need to add the PCH to the Copy Bundle Resources build phase). The reason you're getting that error is because the _managedObjectContext ivar is not getting synthesized, because you're overriding the getter on a read-only property. You either need to change the property to be readwrite (which I wouldn't recommend), redefine the property as readwrite in a class extension, or define the ivar manually in a class extension or the implementation block.

Answer 2

For readonly properties you Even implement there is no Ivar created by the compiler. Declare the Variable

NsmanagedObjectContext *_managedObjectContext;