那时我正在失去头发，所以我想我会接触到这里有过使用带有线程和核心数据的 Objective C 经验的优秀人才。我在从主线程访问的 NSPrivateQueue 上下文中的线程上插入托管对象时遇到问题。因此，在较高级别上，我使用 AFNetworking 生成一个线程来发出请求以从服务器检索 JSON 数据，然后将值插入到我的持久存储核心数据中。完成此操作后，我还有另一个线程用于使用 AFNetworking 下载一些二进制数据。我为此设置了 2 个托管上下文，如下所示：
(NSManagedObjectContext *)masterManagedContext {
if (_masterManagedContext != nil) {
return _masterManagedContext;
}
NSPersistentStoreCoordinator *coord = [self coordinator];
if (coord != nil) {
_masterManagedContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
_masterManagedContext.stalenessInterval = 0.0;
[_masterManagedContext performBlockAndWait:^{
[_masterManagedContext setPersistentStoreCoordinator:coord];
}];
}
return _masterManagedContext;
}
// Return the NSManagedObjectContext to be used in the background during sync
- (NSManagedObjectContext *)backgroundManagedContext {
if (_backgroundManagedContext != nil) {
return _backgroundManagedContext;
}
NSManagedObjectContext *masterContext = [self masterManagedContext];
if (masterContext != nil) {
_backgroundManagedContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
_backgroundManagedContext.stalenessInterval = 0.0;
[_backgroundManagedContext performBlockAndWait:^{
[_backgroundManagedContext setParentContext:masterContext];
}];
}
return _backgroundManagedContext;
}
如上所示，我正在使用子上下文和父上下文。当我打电话来获取 json 数据时，我有如下内容：
AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
//Initially delete all records in table. This will change
[[Singleton sharedInstance]removeEntityObjects:className];
for (int x=0; x < [JSON count]; x++) {
NSMutableDictionary *curDict = [JSON objectAtIndex:x];
[[CoreDatam sharedinstance] insertEmployeesWithDictionary:curDict];
}else {
/* do nothing */
}
}
}
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error,id JSON) {
[delegate performSelector:@selector(didNotCompleteSync:) withObject:className];
}];
[operations addObject:operation];
}
[self.AFClient enqueueBatchOfHTTPRequestOperations:operations progressBlock:^(NSUInteger numberOfCompletedOperations, NSUInteger totalNumberOfOperations) {
NSLog(@"Currenlty downloaded table data %d of %d!",numberOfCompletedOperations,totalNumberOfOperations);
} completionBlock:^(NSArray *operations) {
if (_syncInProgress) {
[[CoreDatam sharedInstance]updateEmpForId];
[self downloadAllFiles];
}
}];
}`
对于插入功能，我有如下内容：
insertEmployeesWithDictionary:curDict {
[[self backgroundManagedContext]performBlockAndWait:^{
Employee *emp = [NSEntityDescription insertNewObjectForEntityForName:@"Employee"
inManagedObjectContext:[self backgroundManagedContext]];
/* Issues saving null into core data based on type.*/
[emp setFirst:[dictCopy objectForKey:@"first"]];
[emp setLast:[dictCopy objectForKey:@"last"]];
NSError *error = nil;
BOOL saved;
saved = [[self backgroundManagedContext] save:&error];
if (!saved) {
NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
}
[self saveMasterContext];
}];
}
问题如下，我试图在上面完成块中的方法中访问托管对象：
updateEmpId {
[self.backgroundManagedContext performBlockAndWait:^{
NSError *error = nil;
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Employee"];
[request setSortDescriptors:[NSArray arrayWithObject:
[NSSortDescriptor sortDescriptorWithKey:@"last" ascending:YES]]];
myEmps = [self.backgroundManagedContext executeFetchRequest:request error:nil];
for (Employee *moEmp in myEmps) {
[[self backgroundManagedContext]refreshObject:moEmp mergeChanges:YES];
moEmp.photo = @'default.pic';
}
NSError *saveError = nil;
if (![self.backgroundManagedContext save:&saveError]) {
NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
}
[self saveMasterContext];
}
问题是，在查看在主线程中修改的托管对象时，我的行为非常不一致。使用父子上下文关系时是否仍然需要传递托管的objectIds？如果是这样，我该怎么做上面的例子？非常感谢任何帮助。