我正在创建一个OSX应用程序，我正在尝试从名为Service的CoreData Entity中加载我的实体。我正在使用默认的Xcode模板，它可以保存我的实体。然而，检索它们会引发此错误。
+ entityForName：nil不是合法的NSManagedObjectContext参数，用于搜索实体名称“Service”
以下是抛出错误的代码，此函数在 awakeFromNib
中调用-( NSMutableArray * )getServices {
//NSManagedObjectContext *context = [(SAAppDelegate *)[[NSApplication sharedApplication] delegate] managedObjectContext];
SAAppDelegate *delegate = (SAAppDelegate*)[[NSApplication sharedApplication] delegate];
NSManagedObjectContext *context = [delegate managedObjectContext];
NSLog(@"After managedObjectContext: %@", context);
NSEntityDescription *entity = [ NSEntityDescription entityForName:@"Service" inManagedObjectContext: context ];
NSSortDescriptor *sortDescriptor = [ [ NSSortDescriptor alloc] initWithKey: @"service_name" ascending: YES ];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];
[request setSortDescriptors:[ NSArray arrayWithObject: sortDescriptor]];
[context processPendingChanges];
NSError *error;
return [ NSMutableArray arrayWithArray: [ context executeFetchRequest:request error:&error ] ];
}
此处的参考是AppDelegate.m文件中的managedObjectContext。
//
// SAAppDelegate.m
// ServerAngel
//
// Created by Adam Bulmer on 29/10/2013.
// Copyright (c) 2013 Adam Bulmer. All rights reserved.
//
#import "SAAppDelegate.h"
@implementation SAAppDelegate
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize managedObjectContext = _managedObjectContext;
@class SAServerListWindowController;
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
// Insert code here to initialize your application
}
// Returns the directory the application uses to store the Core Data store file. This code uses a directory named "com.adambulmer.ServerAngel" in the user's Application Support directory.
- (NSURL *)applicationFilesDirectory
{
NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *appSupportURL = [[fileManager URLsForDirectory:NSApplicationSupportDirectory inDomains:NSUserDomainMask] lastObject];
return [appSupportURL URLByAppendingPathComponent:@"com.adambulmer.ServerAngel"];
}
// Creates if necessary and returns the managed object model for the application.
- (NSManagedObjectModel *)managedObjectModel
{
if ( _managedObjectModel == nil ) {
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"ServerAngel" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
}
return _managedObjectModel;
}
// Returns the persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it. (The directory for the store is created, if necessary.)
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
if ( _persistentStoreCoordinator == nil ) {
NSManagedObjectModel *mom = [ self managedObjectModel ];
NSFileManager *fileManager = [ NSFileManager defaultManager ];
NSURL *applicationFilesDirectory = [ self applicationFilesDirectory ];
NSError *error = nil;
NSDictionary *properties = [ applicationFilesDirectory resourceValuesForKeys:@[ NSURLIsDirectoryKey ] error:&error ];
if ( ! properties ) {
BOOL ok = NO;
if ( [ error code ] == NSFileReadNoSuchFileError ) {
ok = [ fileManager createDirectoryAtPath:[ applicationFilesDirectory path ] withIntermediateDirectories:YES attributes:nil error:&error ];
}
if ( ! ok ) {
[ [ NSApplication sharedApplication ] presentError:error ];
NSLog( @"1 - test" );
return nil;
}
} else {
if ( ! [ properties[ NSURLIsDirectoryKey ] boolValue ] ) {
// Customize and localize this error.
NSString *failureDescription = [NSString stringWithFormat:@"Expected a folder to store application data, found a file (%@).", [applicationFilesDirectory path]];
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setValue:failureDescription forKey:NSLocalizedDescriptionKey];
error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:101 userInfo:dict];
[ [ NSApplication sharedApplication ] presentError:error ];
NSLog( @"2 - test" );
return nil;
}
}
NSURL *url = [applicationFilesDirectory URLByAppendingPathComponent:@"ServerAngel.storedata"];
NSPersistentStoreCoordinator *coordinator = [ [ NSPersistentStoreCoordinator alloc ] initWithManagedObjectModel:mom ];
if ( ! [ coordinator addPersistentStoreWithType:NSXMLStoreType configuration:nil URL:url options:nil error:&error ] ) {
[ [ NSApplication sharedApplication] presentError:error ];
return nil;
}
NSLog(@"AppDelegate coordinator: %@", coordinator);
_persistentStoreCoordinator = coordinator;
}
return _persistentStoreCoordinator;
}
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
- (NSManagedObjectContext *)managedObjectContext
{
if ( _managedObjectContext == nil ) {
_managedObjectContext = [ [ NSManagedObjectContext alloc ] init ];
NSPersistentStoreCoordinator *coordinator = [ self persistentStoreCoordinator ];
if ( coordinator != nil ) {
[ _managedObjectContext setPersistentStoreCoordinator: coordinator ];
}
NSLog(@"AppDelegate coordinator: %@", coordinator);
}
NSLog(@"AppDelegate managedObjectContext: %@", _managedObjectContext);
return _managedObjectContext;
}
// Returns the NSUndoManager for the application. In this case, the manager returned is that of the managed object context for the application.
- (NSUndoManager *)windowWillReturnUndoManager:(NSWindow *)window
{
return [[self managedObjectContext] undoManager];
}
// Performs the save action for the application, which is to send the save: message to the application's managed object context. Any encountered errors are presented to the user.
- (IBAction)saveAction:(id)sender
{
NSError *error = nil;
if (![[self managedObjectContext] commitEditing]) {
NSLog(@"%@:%@ unable to commit editing before saving", [self class], NSStringFromSelector(_cmd));
}
if (![[self managedObjectContext] save:&error]) {
[[NSApplication sharedApplication] presentError:error];
}
}
- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender
{
// Save changes in the application's managed object context before the application terminates.
if (!_managedObjectContext) {
return NSTerminateNow;
}
if (![[self managedObjectContext] commitEditing]) {
NSLog(@"%@:%@ unable to commit editing to terminate", [self class], NSStringFromSelector(_cmd));
return NSTerminateCancel;
}
if (![[self managedObjectContext] hasChanges]) {
return NSTerminateNow;
}
NSError *error = nil;
if (![[self managedObjectContext] save:&error]) {
// Customize this code block to include application-specific recovery steps.
BOOL result = [sender presentError:error];
if (result) {
return NSTerminateCancel;
}
NSString *question = NSLocalizedString(@"Could not save changes while quitting. Quit anyway?", @"Quit without saves error question message");
NSString *info = NSLocalizedString(@"Quitting now will lose any changes you have made since the last successful save", @"Quit without saves error question info");
NSString *quitButton = NSLocalizedString(@"Quit anyway", @"Quit anyway button title");
NSString *cancelButton = NSLocalizedString(@"Cancel", @"Cancel button title");
NSAlert *alert = [[NSAlert alloc] init];
[alert setMessageText:question];
[alert setInformativeText:info];
[alert addButtonWithTitle:quitButton];
[alert addButtonWithTitle:cancelButton];
NSInteger answer = [alert runModal];
if (answer == NSAlertAlternateReturn) {
return NSTerminateCancel;
}
}
return NSTerminateNow;
}
@end
错误日志
2013-11-14 22:01:38.267 ServerAngel[1012:303] Network check
2013-11-14 22:01:48.161 ServerAngel[1012:303] network avi
2013-11-14 22:01:48.162 ServerAngel[1012:303] After managedObjectContext: (null)
2013-11-14 22:01:48.162 ServerAngel[1012:303] +entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Service'
2013-11-14 22:01:48.163 ServerAngel[1012:303] (
0 CoreFoundation 0x00007fff877c941c __exceptionPreprocess + 172
1 libobjc.A.dylib 0x00007fff85c31e75 objc_exception_throw + 43
2 CoreData 0x00007fff8d202729 +[NSEntityDescription entityForName:inManagedObjectContext:] + 217
3 ServerAngel 0x0000000100002d9d -[SAServerListWindowController getServices] + 205
4 ServerAngel 0x0000000100003294 -[SAServerListWindowController checkServices] + 148
5 Foundation 0x00007fff894d1094 __NSFireTimer + 96
6 CoreFoundation 0x00007fff87730724 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
7 CoreFoundation 0x00007fff8773025f __CFRunLoopDoTimer + 1151
8 CoreFoundation 0x00007fff877a176a __CFRunLoopDoTimers + 298
9 CoreFoundation 0x00007fff876ebaa5 __CFRunLoopRun + 1525
10 CoreFoundation 0x00007fff876eb275 CFRunLoopRunSpecific + 309
11 HIToolbox 0x00007fff8e4b3f0d RunCurrentEventLoopInMode + 226
12 HIToolbox 0x00007fff8e4b3cb7 ReceiveNextEventCommon + 479
13 HIToolbox 0x00007fff8e4b3abc _BlockUntilNextEventMatchingListInModeWithFilter + 65
14 AppKit 0x00007fff8ef1828e _DPSNextEvent + 1434
15 AppKit 0x00007fff8ef178db -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 122
16 AppKit 0x00007fff8ef0b9cc -[NSApplication run] + 553
17 AppKit 0x00007fff8eef6803 NSApplicationMain + 940
18 ServerAngel 0x00000001000049a2 main + 34
19 libdyld.dylib 0x00007fff88cbf5fd start + 1
)
2013-11-14 22:01:48.255 ServerAngel[1012:303] Network check
答案 0 :(得分：2)
您的managedObjectContext未针对所有情况进行实例化。您可以简化访问器并确保MOC永远不会使用此访问器。
- (NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext == nil)
{
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:[self persistentStoreCoordinator]];
}
return _managedObjectContext;
}
您可能需要以类似的方式更改persistantStoreCoordinator的访问者，以确保它也懒惰地实例化。
答案 1 :(得分：2)
您的托管对象上下文的访问器方法未被调用 - 您甚至没有看到延迟加载方法中的日志。
我的猜测是应用程序委托未正确连接。如果你使用调试器，你可能会看到这一行：
SAAppDelegate *delegate = (SAAppDelegate*)[[NSApplication sharedApplication] delegate];
正在返回nil。
OS X应用程序默认没有委托，您必须专门设置它们，通常是通过向主xib文件添加一个对象，将其标识为您的委托类并将其连接到应用程序对象的委托出口。
如果已连接（并且因为你说你已经使用了默认模板，所以开箱即用的所有内容都有），那么问题必须是你从错误的{{{ 1}}方法或者您添加了一些其他没有正确设置的nib文件。