CoreData: Accessing the instance of NSManagedObject - ios

Question

I have 3 Scenes each collecting User's input. Each Scene has 5 UITextFields. The 4th Scene shows all the 15 Text Field in a UITableView.
I'm not sure if this is the best way to do do this, but I have the following code for scene 1:
//Meetings is NSManagedObject class. Meetings.h and .m was created from the Meetings entity from Core Data
//I have this code once in the file right before I start saving the data
Meetings *meetings = (Meetings *) [NSEntityDescription insertNewObjectForEntityForName:#"Meetings" inManagedObjectContext:self.managedObjectContext];
// I have similar code below for each user's input.
NSString *date = [[NSString alloc] initWithFormat:#"%#", [dateFormatter stringFromDate:selectedDate]];
DateLabel.text = date;
[meetings setDateLabel:date];
...
[meetings setTimeLabel:time];
..
//Code below is to save. I have this once at the end of the file to save the data
NSError *error = nil;
if (![managedObjectContext save:&error]) {
// Handle the error.
}
//The log below shows the saved data fine. Thus, the data is being saved in managnedObjectContext.
NSLog (#"This is the DateLabel %#", meetings.DateLabel);
Question: How do I access the pointer *meetings from Scene 2 and 3 to save rest of the fields in managedObjectContext? I did a NSLog from Scene 2 and it shows as Null:
//In Scene 2 viewDidLoad method I did the following to check:
self.managedObjectContext = [(STAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
Meetings *meetings = (Meetings *) [NSEntityDescription insertNewObjectForEntityForName:#"Meetings" inManagedObjectContext:self.managedObjectContext];
NSLog (#"This is the DateLabel from Scene 2 %#", meetings.DateLabel);
The log shows:
2013-02-11 18:04:05.447 MyApp[3505:c07] This is the DateLabel from Scene 2 (null)

Answer 1

You either need to pass a pointer to the Meetings object from the previous screens forward to the next by storing them in a property, or you can pass the object's id's and fetch them as needed for the final screen.
Assume the following is a reflection of your code. The class names may not be identical, but I think you will be able follow and change them as needed.
Scene 1 Header File:
//
// Scene1ViewController.h
// ... etc.
#import <UIKit/UIKit.h>
#import "Meetings.h"
#interface Scene1ViewController : UIViewController
#property (nonatomic, strong) Meetings *meetingsForScene1;
// ... etc.
#end
Scene 2 Header File:
//
// Scene2ViewController.h
// ... etc.
#import <UIKit/UIKit.h>
#import "Meetings.h"
#interface Scene2ViewController : UIViewController
#property (nonatomic, strong) Meetings *meetingsFromScene1;
#property (nonatomic, strong) Meetings *meetingsForScene2;
// ... etc.
#end
meetingsForScene2 may or may not be appropriate depending on your requirements. You might just add data from Scene2 to the meetingsFromScene1 and pass that instance on to the next scene.
Scene 1 Implementation's -prepareForSegue:sender::
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
UIViewController *destinationViewController = segue.destinationViewController;
if ([segue.identifier isEqualToString:#"YourSegueIdentifierForTransistionFromScene1ToScene2"]) {
Scene2ViewController *scene2 = [destinationViewController isKindOfClass:[Scene2ViewController class]] ? (Scene2ViewController *)destinationViewController : nil;
NSAssert(scene2, #"scene2 should not be nil");
NSAssert(self.meetingsForScene1, #"self.meetingsForSecen1 should not be nil");
scene2.meetingsFromScene1 = self.meetingsForScene1;
}
}
Note you might have two properties on Scene2. One for the current scene's data and one for the previous scene's data. The important property is the one that holds the data from the previous scene. The -prepareForSegue:sender: method in Scene1 is an appropriate time to set Scene1's data to the property on Scene2.
I've included some NSAssert calls to do some checking. Consider removing those in your production code. Also, note the check when assigning *scene2. If your destination controller is not the right "kind", you'll find out right away.
I am not necessarily advocating this approach as the "best" for your problem, but this approach will at least provide a path to a solution, if not address the issue entirely.

Answer 2

Well, what you do in your viewDidLoad method is creating a new object in your NSManagedObjectContext instance.
What you should do is to make a fetch request for your previously created Meetings object.
Maybe you should read a tutorial about Core Data. The following is very easy to understand: http://www.raywenderlich.com/934/core-data-on-ios-5-tutorial-getting-started