After setting one NSManaged object to another it returns Null

I am trying to pass the selected object in my coredata from the ro开发者_开发知识库otviewcontroller to the edit view. The selected object is being passed but is then becoming null after the theObject=selectedObject is being called. Anyone know what im doing wrong?

This is in the edit.h

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
#import "LearningAppDelegate.h"
@interface edit : UIViewController <UITextViewDelegate, UITableViewDelegate, UITableViewDataSource, UIActionSheetDelegate>{
UITableView *tableView;
NSManagedObject *theObject;
UITextView *messageView;
}
@property(nonatomic, retain) IBOutlet UITableView *tableView;
@property(nonatomic, retain) IBOutlet UITextView *messageView;
@property(nonatomic, retain) NSManagedObject *theObject;
-(id)initWithObject:(NSManagedObject *)selectedObject;
@end

This is in the edit.m:

-(id)initWithObject:(NSManagedObject *)selectedObject {
        self = [super init];
        if (nil == self) {
            return nil;
        }
        NSLog(@"selectedObject: %@", selectedObject);
        NSLog(@"selecetedObject.message: %@", [[selectedObject valueForKey:@"message"] description]);
        theObject=selectedObject;
        NSLog(@"theObject 1: %@", theObject);
        NSLog(@"theObject.message 1: %@", [[theObject valueForKey:@"message"] description]);
        return self;
    }

    // Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
    - (void)viewDidLoad {
        NSLog(@"theObject 2: %@", theObject);
        NSLog(@"theObject.message 2: %@", [[theObject valueForKey:@"message"] description]);
        messageView.text=[[theObject valueForKey:@"message"] description];
        [super viewDidLoad];
    }

I am actually amazed that doesn't crash for you. You're assigning the variable selectedObject into the instance variable theObject without retaining it for your own use. By accessing the instance variable directly in the assignment 'theObject=selectedObject', you're bypassing the behavior granted by the @property declaration. This means that once selectedObject is finally dealloc'd, theObject will point to garbage memory.

The correct way to do this is to put theObject = [selectedObject retain]; in the -initWithObject: method and in -viewDidLoad to access it via self.theObject rather than just theObject.

In my own usage I prefer to give instance variables names different from the actual property name to avoid confusion. For example:

@interface SomeClass : NSObject
{
    @private
    NSManagedObject *_theObject;
}

@property (nonatomic, retain) NSManagedObject *theObject;

...

@end


@implementation SomeClass
@synthesize theObject = _theObject

...

- (void)dealloc
{
    [_theObject release], _theObject = nil;
    [super dealloc];
}

@end

I only have experience with Coredata on the desktop, but the problem looks like it would be with your initWithObject method. At no point do you actually insert the new object into the managed object context. You should be using this method to make new objects:

- (id)initWithEntity:(NSEntityDescription *)entity insertIntoManagedObjectContext:(NSManagedObjectContext *)context

As an example in pseudocode:

NSManagedObject *newObject = [[NSManagedObject alloc] initWithEntity:NSENTITYDESCRIPTION insertIntoManagedObjectContext:MANAGEDOBJECTCONTEXT];
[newObject setValue:@"VALUE_OF_SELECTED_OBJECT" forKey:@"APPROPRIATE_KEY"];
//REPEAT AS NECESSARY
[MANAGEDOBJECTCONTEXT save];

*Code not tested, naming conventions are ignored, etc.

The save is important. If you don't do this the object won't persist.