扩展教程材料时出现entityForName和ManagedObjectContext问题

下午所有，

我尝试在（位置）coredata教程代码中向持久性存储添加第二个数据实体，然后在新视图中访问它。 我认为我已经按照教程，并检查我正在做一个干净的构建等，但无法看到要改变什么，以防止它崩溃。

我担心我会因为这个而斗智斗勇，似乎无法找到我错过的那一步。 我已粘贴下面的标题和代码文件，如果我需要共享更多代码，请告诉我。 崩溃似乎发生在线上：

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Album" inManagedObjectContext:[self managedObjectContext]]; 

代码中还有另一行引用了galleryviewcontroller，这是在主应用程序委托中：

 galleryViewController.managedObjectContext = [self managedObjectContext]; 

GalleryViewController.h

 #import  @interface GalleryViewController : UIViewController { NSManagedObjectContext *managedObjectContext; int rowNumber; IBOutlet UILabel *lblMessage; UIBarButtonItem *addButton; NSMutableArray *imagesArray; } @property (readwrite) int rowNumber; @property (nonatomic,retain) UILabel *lblMessage; @property (nonatomic,retain) NSMutableArray *imagesArray; @property (nonatomic, retain) NSManagedObjectContext *managedObjectContext; @property (nonatomic, retain) UIBarButtonItem *addButton; -(void)updateRowNumber:(int)theIndex; -(void)addImage; @end 

GalleryViewController.m

 #import "RootViewController.h" #import "LocationsAppDelegate.h" #import "Album.h" #import "GalleryViewController.h" #import "Image.h" @implementation GalleryViewController @synthesize lblMessage,rowNumber,addButton,managedObjectContext; @synthesize imagesArray; /* // The designated initializer. Override if you create the controller programmatically and want to perform customization that is not appropriate for viewDidLoad. - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { if ((self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil])) { // Custom initialization } return self; } */ -(void)updateRowNumber:(int)theIndex{ rowNumber=theIndex; LocationsAppDelegate *mainDelegate =(LocationsAppDelegate *)[[UIApplication sharedApplication] delegate]; Album *anAlbum = [mainDelegate.albumsArray objectAtIndex:rowNumber]; lblMessage.text = anAlbum.uniqueAlbumIdentifier; } // Implement viewDidLoad to do additional setup after loading the view, typically from a nib. - (void)viewDidLoad { [super viewDidLoad]; addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addImage)]; addButton.enabled = YES; self.navigationItem.rightBarButtonItem = addButton; /* Found this in another answer, adding it to the code didn't help. if (managedObjectContext == nil) { managedObjectContext = [[[UIApplication sharedApplication] delegate] managedObjectContext]; } */ NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Album" inManagedObjectContext:[self managedObjectContext]]; [request setEntity:entity]; // Order the albums by creation date, most recent first. NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"imagePath" ascending:NO]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; [request setSortDescriptors:sortDescriptors]; [sortDescriptor release]; [sortDescriptors release]; // Execute the fetch -- create a mutable copy of the result. NSError *error = nil; NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy]; if (mutableFetchResults == nil) { // Handle the error. } [self setImagesArray:mutableFetchResults]; int a = 5; int b = 10; for( int i=0; i<[imagesArray count]; i++ ) { if( a == 325 ) { a = 5; b += 70; } UIImageView *any = [[UIImageView alloc] initWithFrame:CGRectMake(a,b,70,60)]; any.image = [imagesArray objectAtIndex:i]; any.tag = i; [self.view addSubview:any]; [any release]; a += 80; } } -(void)addImage{ NSString *msg = [NSString stringWithFormat:@"%i",rowNumber]; UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Add image to" message:msg delegate:self cancelButtonTitle:@"No" otherButtonTitles:@"Yes", nil]; [alert show]; [alert release]; } - (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use. } - (void)viewDidUnload { [super viewDidUnload]; } - (void)dealloc { [lblMessage release]; [managedObjectContext release]; [super dealloc]; } @end 

Answer 1

它有助于发布您获得的错误。

您是否尝试过以下方法：

• 清理项目的构建
• 重置模拟器以删除旧的sqlite数据文件

如果这些都没有解决问题，那么将您收到的错误发布为您的问题的更新。

更新

我正在寻找的信息将在控制台中打印出来，而调试器是一个无限有用的工具，我建议学习它，在这种情况下，您的问题将通过查看应用程序的控制台输出来解决。