ios - CoreData、UIManagedDocument 和空持久存储

Question

我正在使用 UIManagedDocument 读取和写入 CoreData。我有 Document 类。这是一些教程中的文档:

.h

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

typedef void (^OnDocumentReady) (UIManagedDocument *document);

@interface Document : NSObject

@property (strong, nonatomic) UIManagedDocument *document;

+ (Document *)sharedDocument;
- (void)performWithDocument:(OnDocumentReady)onDocumentReady;

@end

.m

@interface Document ()
- (void)objectsDidChange:(NSNotification *)notification;
- (void)contextDidSave:(NSNotification *)notification;
@end;

@implementation Document

@synthesize document = _document;

static Document*_sharedInstance;

+ (Document *)sharedDocument
{
    static dispatch_once_t once;
    dispatch_once(&once, ^{
        _sharedInstance = [[self alloc] init];
    });

    return _sharedInstance;
}

- (id)init {
    self = [super init];
    if (self) {
        NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
        url = [url URLByAppendingPathComponent:@"Document"];
        self.document = [[UIManagedDocument alloc] initWithFileURL:url];

        NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                                 [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                                 [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];
        self.document.persistentStoreOptions = options;

        // Register for notifications
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(objectsDidChange:)
                                                     name:NSManagedObjectContextObjectsDidChangeNotification
                                                   object:self.document.managedObjectContext];

        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(contextDidSave:)
                                                     name:NSManagedObjectContextDidSaveNotification
                                                   object:self.document.managedObjectContext];
    }
    return self;
}

- (void)performWithDocument:(OnDocumentReady)onDocumentReady
{
    void (^OnDocumentDidLoad)(BOOL) = ^(BOOL success) {
        onDocumentReady(self.document);
    };

    if (![[NSFileManager defaultManager] fileExistsAtPath:[self.document.fileURL path]]) {
        [self.document saveToURL:self.document.fileURL
                forSaveOperation:UIDocumentSaveForCreating
               completionHandler:OnDocumentDidLoad];
    } else if (self.document.documentState == UIDocumentStateClosed) {
        [self.document openWithCompletionHandler:OnDocumentDidLoad];
    } else if (self.document.documentState == UIDocumentStateNormal) {
        OnDocumentDidLoad(YES);
    }
}

- (void)objectsDidChange:(NSNotification *)notification
{
#ifdef DEBUG
    NSLog(@"NSManagedObjects did change.");
#endif
}

- (void)contextDidSave:(NSNotification *)notification
{
#ifdef DEBUG
    NSLog(@"NSManagedContext did save.");
#endif
}

@end

然后在 ViewController 中我有 NSURLConnection:

-(void)connectionDidFinishLoading:(NSURLConnection *)connection {
    DataParser *parser = [[DataParser alloc] init];
    [parser startParsingData:self.myMutableData withContext:self.moc];
}

然后我在这里打开文档:

-(void)initDocument {
    if (!self.moc) {
        [[Document sharedDocument] performWithDocument:^(UIManagedDocument *document) {
            self.moc = document.managedObjectContext;
            [[NSNotificationCenter defaultCenter] postNotificationName:UIDocumentStateChangedNotification object:self];

            NSURLRequest *request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:@"someURL"] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60];
            [NSURLConnection connectionWithRequest:request delegate:self];
        }];
    }
}

然后我尝试解析数据:

-(void)startParsingData:(NSData*)data withContext:(NSManagedObjectContext*)context {
    self.moc = context;
    self.startDate = [NSDate date];
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
    parser.delegate = self;
    [parser parse];
}

ant 尝试在 XML 解析后将其加载到核心数据中:

-(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {
    if([elementName isEqualToString:@"Item"]) {
            [self.moc performBlockAndWait:^{
                TestEntity *te = [NSEntityDescription insertNewObjectForEntityForName:@"TestEntity" inManagedObjectContext:self.moc];
                te.surname = @"5433fds";
                te.name = @"5342fdsfsd";
            }];
    }
}

我看到了日志:

2014-01-24 16:21:21.692 Ce[85149:70b] NSManagedObjects did change.
2014-01-24 16:21:36.696 Ce[85149:70b] NSManagedContext did save.

所以我假设这应该在 sqlite 文件中，但是当我尝试读取它时它完全是空的。 awl 文件有一些更大的大小，但 persistentStore 有 0 行。为什么？

Answer 1

当您第二次启动应用程序时会发生什么，您能看到应用程序中的数据吗？

在 iOS 7 中，SQLite 现在启用了日志功能。我想知道日志记录是否引起了困惑(数据存在但还没有在 sqlite 文件中)。

我还会质疑您为什么使用 UIManagedDocument。看来您在单例模式中使用核心数据(这很糟糕)，然后在该单例模式中使用 UIManagedDocument(更糟)。

UIManagedDocument 适用于基于文档的应用程序。您可能会违反该类中的一些“自动化”功能，如果您改为构建标准的 Core Data 堆栈，这些功能很容易清除。

您可能会考虑关闭 Journaling，为您的 NSPersistentStoreCoordinator 添加 vacuum 选项或切换到标准的 Core Data 堆栈。