我正在使用Core Data开发iOS应用。我有一个Log实体，与Audio，Photo个实体以及与one-to-one实体的Status关系具有一对多的关系。该日志还具有text，longitude，latitude属性。我可以创建日志，更改其属性，添加status实体，这些更改将显示正确，直到我退出应用程序。所有的更改都会消失，而我正在查看sqlite数据库，所有这些更改都从未在数据库中持久化。在数据库中，只会创建status对象，但不会链接到log对象。
但是，如果我在audio或photo中添加log.audioSet或log.photoSet个对象，我对log所做的更改，包括text的更改{1}}或status将突然保存到数据库中。
因此，只有在添加了相关的one_to_many实体并且NSManagedObjectContext突然开始工作之后，才会在[[LTLogStore sharedStore] saveChanges]中维护更改。
我正在使用单身人士来管理NSManagedObjectContext。有什么想法吗？
如果相关，我会发布一些代码。感谢。
更新：我不确定这些代码是否足够。但基本上一切正常，并且显示，它只是不保存到数据库。我正在使用mogenerator设置text和latitude，但由于所有内容都在上下文中。我不确定这是您可能需要的代码。
CODE：
@interface LTLogStore : NSObject{
}
+ (LTLogStore *)sharedStore;
- (void)removeItem:(Log *)p;
- (Log *)createItem;
- (BOOL)saveChanges;
@property(nonatomic, strong) NSFetchedResultsController *resultsController;
@property(nonatomic, strong) NSManagedObjectModel *model;
@property(nonatomic, strong) NSManagedObjectContext *context;
@end
@implementation LTLogStore
@synthesize resultsController;
@synthesize context, model;
+ (LTLogStore *)sharedStore
{
static LTLogStore *sharedStore = nil;
if(!sharedStore){
sharedStore = [[super allocWithZone:nil] init];
}
return sharedStore;
}
+ (id)allocWithZone:(NSZone *)zone
{
return [self sharedStore];
}
- (id)init
{
self = [super init];
if(self) {
model = [NSManagedObjectModel mergedModelFromBundles:nil];
NSPersistentStoreCoordinator *psc =
[[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:model];
// Where does the SQLite file go?
NSString *path = [self itemArchivePath];
NSURL *storeURL = [NSURL fileURLWithPath:path];
NSError *error = nil;
if (![psc addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:storeURL
options:nil
error:&error]) {
[NSException raise:@"Open failed"
format:@"Reason: %@", [error localizedDescription]];
}
// Create the managed object context
context = [[NSManagedObjectContext alloc] init];
[context setPersistentStoreCoordinator:psc];
// The managed object context can manage undo, but we don't need it
[context setUndoManager:nil];
}
return self;
}
- (NSFetchedResultsController *)resultsController {
if (resultsController !=nil) {
return resultsController;
}
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *e = [[model entitiesByName] objectForKey:@"Log"];
[request setEntity:e];
NSSortDescriptor *sd = [NSSortDescriptor
sortDescriptorWithKey:@"created_at"
ascending:NO];
[request setSortDescriptors:[NSArray arrayWithObject:sd]];
[request setReturnsObjectsAsFaults:NO];
NSFetchedResultsController *fetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:request
managedObjectContext:context
sectionNameKeyPath:nil cacheName:@"Root"];
NSError *error;
BOOL success = [fetchedResultsController performFetch:&error];
if (!success) {
//handle the error
}
return fetchedResultsController;
}
- (NSString *)itemArchivePath
{
NSArray *documentDirectories =
NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
NSUserDomainMask, YES);
// Get one and only document directory from that list
NSString *documentDirectory = [documentDirectories objectAtIndex:0];
NSString *storePath = [documentDirectory stringByAppendingPathComponent:@"store.data"];
return storePath;
}
- (BOOL)saveChanges
{
NSError *err = nil;
BOOL successful = [context save:&err];
NSLog(@"Saving changes to the database");
if (!successful) {
NSLog(@"Error saving: %@", [err localizedDescription]);
}
return successful;
}
- (void)removeItem:(Log *)l
{
[context deleteObject:l];
[self saveChanges];
}
- (Log *)createItem
{
Log *p = [NSEntityDescription insertNewObjectForEntityForName:@"Log"
inManagedObjectContext:context];
[self saveChanges];
return p;
}
@end
@interface Log : _Log {
}
//these two are some custom convenience methods for location attributes, but it does the work of setting the longitude and latitude value in the log object, but calling the [[LTLogStore sharedStore] saveChanges] still won't save it into the database.
-(CLLocation*)location;
-(void)setLocation:(CLLocation*)location;
//this all works
-(Audio*)newAudio;
-(Audio*)newAudioWithPath:(NSString*)audioPath;
//after calling this method, even the log.text changes will be saved to the database.
-(void)addAudioWithPath:(NSString*)audioPath;
-(void)removeAudio:(Audio*)audio;
@end
#import "Log.h"
#import "Audio.h"
#import "LTLogStore.h"
@implementation Log
-(CLLocation*)location{
if (!self.longitude || !self.latitude) {
return nil;
}
CLLocation *l = [[CLLocation alloc] initWithLatitude:[self.latitude doubleValue] longitude:[self.longitude doubleValue]];
return l;
}
-(void)setLocation:(CLLocation*)location{
if (location==nil) {
self.latitude = nil;
self.longitude = nil;
}
self.latitude = [NSNumber numberWithDouble: location.coordinate.latitude];
self.longitude = [NSNumber numberWithDouble:location.coordinate.longitude];
[[LTLogStore sharedStore] saveChanges];
}
-(Audio*)newAudio{
Audio *a = [Audio new];
a.log = self;
return a;
}
-(Audio*)newAudioWithPath:(NSString*)audioPath{
Audio *new = [self newAudio];
[new setKey:audioPath];
return new;
}
-(void)addAudioWithPath:(NSString*)audioPath{
Audio *new = [self newAudio];
[new setKey:audioPath];
[[LTLogStore sharedStore] saveChanges];
}
-(void)removeAudio:(Audio*)audio{
[self.audiosSet removeObject:audio];
[[[LTLogStore sharedStore] context] deleteObject:audio];
[[LTLogStore sharedStore] saveChanges];
}
@end
更新：
问题解决了，见答案。
更新问题：为什么我的压倒一切导致问题？有人可以解释核心数据的魔力背后的原因，还是KVO幕后的原因？
答案 0 :(得分：0)
问题解决了，我覆盖了Log类中的willChangeValueForKey方法，这导致了问题，我认为代码是无关紧要的。但它是：
- (void)willChangeValueForKey:(NSString *)key{
//I added the following line to fix my problem
[super willChangeValueForKey:key];
//this is the original line, I want to have this
//because I want to have a isBlank property
//so I can see if the user modified the log
_isBlank = false;
//I tried to also add the following line to be safe.
//turns out this line is not needed, and it will make the problem occur again
//[super didChangeValueForKey:key];
}