从视图控制器传递后，传递的管理对象上下文为null

Question

I'm trying to do a simple core data app. I have the following code in the app delegate:

#import <UIKit/UIKit.h>

@interface HEFTAppDelegate : UIResponder <UIApplicationDelegate>{

}


@property (strong, nonatomic) UIWindow *window;

@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;


@end

Then in the implementation

#import "HEFTAppDelegate.h"
#import "HEFTMasterViewController.h"
#import "HEFTTestdatabaseMasterViewController.h"
#import "HEFTData_Manager.h"

@implementation HEFTAppDelegate

@synthesize window = _window;
@synthesize managedObjectContext = __managedObjectContext;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPad) {

        //ipad init

    } else {
        HEFTTestdatabaseMasterViewController *testDatabaseMasterViewController = [[HEFTTestdatabaseMasterViewController alloc]initWithStyle:UITableViewStylePlain];
        HEFTData_Manager *dataManager = [[HEFTData_Manager alloc]init];

        self.managedObjectContext = [dataManager mainObjectContext];

        // Pass the managed object context to the view controller.

        testDatabaseMasterViewController.managedObjectContext = self.managedObjectContext ;


    }
    return YES;
}

The HEFTData_Manager class sets up the context etc

Looking at the debugger the context appears to get set correctly in the app delegate and when the

testDatabaseMasterViewController.managedObjectContext = self.managedObjectContext ;

Message is issued.

However when the table view appears the HEFTTestdatabaseMasterViewController managedObjectContext is NULL

Any ideas on whats happening and pointers would be gratefully received.

Debugger output

At:

testDatabaseMasterViewController.managedObjectContext = self.managedObjectContext ;

testDatabaseMasterViewController    HEFTTestdatabaseMasterViewController
*   0x06d74b50 UITableViewController    UITableViewController    managedObjectContext   NSManagedObjectContext *    0x06d778e0
fetchedResultsController    NSFetchedResultsController *    0x00000000

At:

- (void)viewDidLoad
{
    [super viewDidLoad];

   // NSManagedObjectContext *context = self.managedObjectContext;

    NSLog(@"context : %@",self.managedObjectContext);

    self.navigationItem.leftBarButtonItem = self.editButtonItem;

    UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(insertNewObject:)];
    self.navigationItem.rightBarButtonItem = addButton;

}

self HEFTTestdatabaseMasterViewController *const 0x06d705a0 UITableViewController UITableViewController
UIViewController UIViewController
_tableViewStyle UITableViewStyle UITableViewStylePlain _keyboardSupport id 0x00000000 _staticDataSource id 0x00000000 _tableViewControllerFlags managedObjectContext NSManagedObjectContext * 0x00000000 fetchedResultsController NSFetchedResultsController * 0x00000000

Answer 1

您应该分配您managedObjectContext属性里面viewDidLoad的方法HEFTTestdatabaseMasterViewController类，或者如果是，你不应该简单地编辑继承它，并把它在一个库文件viewDidLoad的自定义类。

Answer 2

Added:

id appDelegate = (id)[[UIApplication sharedApplication] delegate]; self.managedObjectContext = [appDelegate managedObjectContext];

To the viewDidLoad method of the HEFTTestDatabaseMasterVIewController

Worked and will also work in other classes that need access to the managedObjectContext