ios - managedObjectContext 无法识别的选择器发送到实例

Question

我正在按照教程开发 iOS 应用程序。我正在使用核心数据。应用程序的第一个 View 是 RootViewController。所有核心数据堆栈都在 AppDelegate 文件中。这是 AppDelegate.m 中调用 RootViewController 文件的代码部分:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  // Fetch the data to see if we ought to pre-populate
  NSError *error = nil;
  if (![[self fetchedResultsController] performFetch:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
  }

  [self loadFavoriteThingsData];        

  RootViewController *rootViewController = (RootViewController *)[navigationController topViewController];
  [rootViewController setManagedObjectContext:[self managedObjectContext]];       

  [window addSubview:[navigationController view]];
  [window makeKeyAndVisible];
  return YES;
}

现在，在应用程序的另一部分，我需要打开一个新的 View Controller ，它是 RootViewController 的副本，名为 DoneViewController，但使用其他 NSPredicate s 显示其他核心数据对象。

在 RootViewController 中有一个按钮可以打开 MenuViewController 文件，从那里我尝试使用以下方法打开 DoneViewController:

- (IBAction)doneToDoaction:(id)sender {
    DoneViewController *viewController = [[DoneViewController alloc] init];

    [self presentViewController:viewController animated:YES completion:nil];
}

但是一个异常被触发了:

[MenuViewController managedObjectContext]: unrecognized selector sent to instance 0x145a0c00
2013-12-26 22:58:23.688  *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MenuViewController managedObjectContext]: unrecognized selector sent to instance

我想我必须将 managedObjectContext 从 RootViewController 传递到 MenuViewController，然后从 MenuViewController 传递到 DoneViewController，但我不知道该怎么做。

Answer 1

这是因为您没有使用 NSObject 类。为此，您必须在 AppDelegate.h 中实现 NSObject。像这样..

@interface AppDelegate : UIResponder <UIApplicationDelegate,NSObject>{
    NSManagedObjectModel *managedObjectModel;
    NSManagedObjectContext *managedObjectContext;
    NSPersistentStoreCoordinator *persistentStoreCoordinator;
}

并添加属性。

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

- (NSString *)applicationDocumentsDirectory;

同时在 AppDelegate.m 文件中添加代码...

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

    return managedObjectContext;
}

 - (NSManagedObjectModel *)managedObjectModel {
    if (managedObjectModel != nil) {
        return managedObjectModel;
    }
    managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil] ;

    return managedObjectModel;
}

 - (NSPersistentStoreCoordinator *)persistentStoreCoordinator

 {

    if (persistentStoreCoordinator != nil) {
        return persistentStoreCoordinator;
    }
    NSURL *storeUrl = [NSURL fileURLWithPath: [[self  applicationDocumentsDirectory]
                                               stringByAppendingPathComponent: @"<Project Name>.sqlite"]];
    NSError *error = nil;
    persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]
                                  initWithManagedObjectModel:[self managedObjectModel]];
        if(![persistentStoreCoordinator      addPersistentStoreWithType:NSSQLiteStoreType configuration:nil   URL:storeUrl options:nil error:&error]) 
  {
        /*Error for store creation should be handled in here*/
  }

    return persistentStoreCoordinator;
}
- (NSString *)applicationDocumentsDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}

这对我 100% 有效。希望它对你有用。