是的，我是新手，但我肯定会感谢一些帮助。我有一个相当简单的示例应用程序，我正在努力学习核心数据。我有一个应用程序，它只显示四个文本字段，并允许用户在这四个字段中保存文本。
该应用程序编译，但在执行时，我得到一个“黑色”屏幕。我最初认为我的问题是我的PersitenecCoreDataViewController.xib中的视图由于某种原因没有显示。但是，在我的调试器控制台中，由于未捕获的异常，我发现我的应用程序被终止的位置：
NSInvalidArgumentException'，原因： 'executeFetchRequest：错误：获取 请求必须有实体
我现在认为我没有正确设置我的获取请求。
我的app署名和viewController类代码如下所示。提前感谢您的时间和帮助。 。
// PersistenceCoreDataAppDelegate.h
// Created by RICHARD COLEMAN on 3/21/11.
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
@class PersistenceCoreDataViewController;
@interface PersistenceCoreDataAppDelegate : NSObject <UIApplicationDelegate> {
UIWindow* window;
PersistenceCoreDataViewController* rootController;
@private
NSManagedObjectContext* managedObjectContext_;
NSManagedObjectModel* managedObjectModel_;
NSPersistentStoreCoordinator* persistentStoreCoordinator_;
}
@property (nonatomic, retain) IBOutlet UIWindow* window;
@property (nonatomic, retain, readonly) NSManagedObjectContext* managedObjectContext;
@property (nonatomic, retain, readonly) NSManagedObjectModel* managedObjectModel;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator* persistentStoreCoordinator;
@property (nonatomic, retain) IBOutlet PersistenceCoreDataViewController* rootController;
- (NSString *)applicationDocumentsDirectory;
@end
// PersistenceCoreDataAppDelegate.m
// Created by RICHARD COLEMAN on 3/21/11.
#import "PersistenceCoreDataAppDelegate.h"
#import "PersistenceCoreDataViewController.h"
@implementation PersistenceCoreDataAppDelegate
@synthesize window;
@synthesize rootController;
#pragma mark -
#pragma mark Application lifecycle
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.
[window addSubview:rootController.view];
[window makeKeyAndVisible];
return YES;
}
// applicationWillTerminate: saves changes in the application's managed object context // before the application terminates.
- (void)applicationWillTerminate:(UIApplication *)application {
NSError *error = nil;
if (managedObjectContext_ != nil) {
if ([managedObjectContext_ hasChanges] && ![managedObjectContext_ save:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
}
#pragma mark -
#pragma mark Core Data stack
- (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_;
}
NSString *modelPath = [[NSBundle mainBundle] pathForResource:@"PersistenceCoreData" ofType:@"momd"];
NSURL *modelURL = [NSURL fileURLWithPath:modelPath];
managedObjectModel_ = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return managedObjectModel_;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
if (persistentStoreCoordinator_ != nil) {
return persistentStoreCoordinator_;
}
NSURL *storeURL = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"PersistenceCoreData.sqlite"]];
NSError *error = nil;
persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return persistentStoreCoordinator_;
}
#pragma mark -
#pragma mark Applications Documents directory
- (NSString *)applicationDocumentsDirectory {
return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}
#pragma mark -
#pragma mark Memory management
- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application {
}
- (void)dealloc {
[managedObjectContext_ release];
[managedObjectModel_ release];
[persistentStoreCoordinator_ release];
[window release];
[super dealloc];
}
@end
// PersistenceCoreDataViewController.h
// Created by RICHARD COLEMAN on 3/21/11.
#import <UIKit/UIKit.h>
@interface PersistenceCoreDataViewController : UIViewController {
UITextField* line1;
UITextField* line2;
UITextField* line3;
UITextField* line4;
}
@property (nonatomic, retain) IBOutlet UITextField* line1;
@property (nonatomic, retain) IBOutlet UITextField* line2;
@property (nonatomic, retain) IBOutlet UITextField* line3;
@property (nonatomic, retain) IBOutlet UITextField* line4;
@end
// PersistenceCoreDataViewController.m
// Created by RICHARD COLEMAN on 3/21/11.
#import "PersistenceCoreDataViewController.h"
#import "PersistenceCoreDataAppDelegate.h"
@implementation PersistenceCoreDataViewController
@synthesize line1;
@synthesize line2;
@synthesize line3;
@synthesize line4;
- (void)applicationWillTerminate:(NSNotification *)notification {
// Get a reference to our application delegate, which we then use to get the managed object context,
// i.e. context, that was created for us
// Remember an application delegate performs a specific action at a certain predefined time on behalf
// of the application
PersistenceCoreDataAppDelegate* appDelegate = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext* context = [appDelegate managedObjectContext];
NSError* error;
// Loop to execute 4x, ie. once for each line
for (int i = 1; i <= 4; i++) {
// Obtain field name by appending value of i to line
NSString* fieldName = [NSString stringWithFormat:@" line%d", i];
// Obtain reference to the correct field
UITextField* theField = [self valueForKey:fieldName];
// Create fetch request; remember a fetch request is just a predefined query
NSFetchRequest* request = [[NSFetchRequest alloc] init];
// Create entity description (describing Line entity using correct context we retrieved
// from application delegate) that will be fed to fetch request so it knows what type
// of entity to look for
NSEntityDescription* entityDescription = [NSEntityDescription entityForName:@" Line"
inManagedObjectContext:context];
[request setEntity:entityDescription];
// Create a predicate that identifies the right object for the field (this will help us
// find out if there is already a managed object in the persistent store that corresponds
// to this field
// managed object - instance of entity
// persistent store - area where managed objects exist
NSPredicate* pred = [NSPredicate predicateWithFormat:@"(lineNum = %d)", i];
[request setPredicate:pred];
// Declared pointer and set to nil b/c we don't know yet if we're going to load a managed object
// from the persistent store or create a new one
NSManagedObject* theLine = nil;
// Actually exec the fetch against the given context; rememeber the fetch request is just a query
// and the context is where we manage the state, access, info about properties, etc.
NSArray* objects = [context executeFetchRequest:request error:&error];
// Checking to see if objects are nil; if nil there was an error; handle appropriately
if (objects == nil) {
NSLog(@" There was an error!");
// Do whatever error handling is appropriate
}
// Was an object returned that matched our criteria; if there is one, load it; if not create one
if ([objects count] > 0)
theLine = [objects objectAtIndex:0];
else
theLine = [NSEntityDescription insertNewObjectForEntityForName:@" Line"
inManagedObjectContext:context];
// use key-value coding to set the line number and text for this managed object
[theLine setValue:[NSNumber numberWithInt:i] forKey:@" lineNum"];
[theLine setValue:theField.text forKey:@" lineText"];
[request release];
}
// looping is complete, save changes
[context save:&error];
}
// this method needs to determine if there is any existing data and if so, load it
- (void)viewDidLoad {
// get a reference to the application delegate and use it to get a pointer to the application's
// default context
PersistenceCoreDataAppDelegate* appDelegate = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext* context = [appDelegate managedObjectContext];
// Create an Entity Description that describes our entity
NSEntityDescription* entityDescription = [NSEntityDescription entityForName:@" Line"
inManagedObjectContext:context];
// Create a fetch request, i.e. a query, and pass it the entity description so it knows what type
// of objects to retriev
NSFetchRequest* request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
// We don't create a predicate as we want to retrieve all Line objects in the persistent store
NSError* error;
NSArray* objects = [context executeFetchRequest:request error:&error];
// Ensure we get back a valid array
if (objects == nil) {
NSLog(@" There was an error!");
// Do whatever error handling is appropriate
}
// Using fast enumeration to loop thru array of retrieved managed objects pulling out the lineNum
// and lineText and updating one of the text fields on our user interface
for (NSManagedObject* oneObject in objects) {
NSNumber* lineNum = [oneObject valueForKey:@" lineNum"];
NSString* lineText = [oneObject valueForKey:@" lineText"];
NSString* fieldName = [NSString stringWithFormat:@" line%@", lineNum];
UITextField* theField = [self valueForKey:fieldName];
theField.text = lineText;
}
[request release];
// Register to be notified when the app is about to terminate so you can save any changes the user
// has made to the data
UIApplication *app = [UIApplication sharedApplication];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(applicationWillTerminate:)
name:UIApplicationWillTerminateNotification
object:app];
[super viewDidLoad];
}
// Override to allow orientations other than the default portrait orientation.
-(BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
// Return YES for supported orientations
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
- (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 {
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
self.line1 = nil;
self.line2 = nil;
self.line3 = nil;
self.line4 = nil;
[super viewDidUnload];
}
- (void)dealloc {
[line1 release];
[line2 release];
[line3 release];
[line4 release];
[super dealloc];
}
@end
答案 0 :(得分：0)
@ Julien和fluchtpunkt ..我也很新，我想知道是否有空间会导致问题？
我可能错了但看到你的错误消息“获取请求必须有一个实体”让我想知道你是否确实使用核心数据创建了实体和相关属性？这是我想到的第一件事。让我知道..