Cocoa 使用NSPersistentDocument读取和写入元数据的理想位置？
在我的NSPersistentDocument子类中，我需要在保存文档时将一些元数据保存到文档中，当然，在打开文档时将其读回。我确实让它工作了，但我不确定这是否是正确的处理方式。（我的测试反映了一个新的、未保存的文档被保存，然后再次打开。新的、未保存的文档在第一次保存后才分配NSPersistentStore。） 以下是我的工作代码，以及与我的测试和如何处理此问题的思考过程相关的注释：Cocoa 使用NSPersistentDocument读取和写入元数据的理想位置？,cocoa,core-data,Cocoa,Core Data,在我的NSPersistentDocument子类中，我需要在保存文档时将一些元数据保存到文档中，当然，在打开文档时将其读回。我确实让它工作了，但我不确定这是否是正确的处理方式。（我的测试反映了一个新的、未保存的文档被保存，然后再次打开。新的、未保存的文档在第一次保存后才分配NSPersistentStore。） 以下是我的工作代码，以及与我的测试和如何处理此问题的思考过程相关的注释： - (BOOL)readFromURL:(NSURL *)absoluteURL ofType:(NSStri
- (BOOL)readFromURL:(NSURL *)absoluteURL ofType:(NSString *)typeName error:(NSError **)outError
{
// No persistent store available yet
BOOL result = [super readFromURL:absoluteURL ofType:typeName error:outError];
// Persistent store available, but metadata may be already altered by configurePersistentStoreCoordinatorForURL:
// if I were set the data there instead of in writeToURL:
if (result == YES)
{
// Read metadata
NSPersistentStore *persistentStore = [self.managedObjectContext.persistentStoreCoordinator persistentStoreForURL:absoluteURL];
NSString * uuid = [persistentStore metadata][DefaultLocationUUIDKey];
self.defaultLocationUUID = uuid;
}
return result;
}
- (BOOL)writeToURL:(NSURL *)absoluteURL ofType:(NSString *)typeName forSaveOperation:(NSSaveOperationType)saveOperation originalContentsURL:(NSURL *)absoluteOriginalContentsURL error:(NSError **)error
{
// No persistent store available yet
BOOL result = [super writeToURL:absoluteURL ofType:typeName forSaveOperation:saveOperation originalContentsURL:absoluteOriginalContentsURL error:error];
// Persistent store available, but has already been saved by this point
// Get mutable copy of existing metadata and update with new data
NSPersistentStore *persistentStore = [self.managedObjectContext.persistentStoreCoordinator persistentStoreForURL:absoluteURL];
NSMutableDictionary *metadata = [persistentStore.metadata mutableCopy];
metadata[DefaultLocationUUIDKey] = self.defaultLocationUUID;
// Use this method because it saves the metadata directly to the file without having to re-save the document, is this correct? It works.
// Are their negative side effects to altering the metadata in this way while the file is open? I haven't tested all possibilities.
NSError *metadataError = nil;
[NSPersistentStoreCoordinator setMetadata:metadata forPersistentStoreOfType:typeName URL:absoluteURL error:&metadataError];
return result;
}
// Called for both open and save, but not for new documents (which is fine, use initWithType:error:)
- (BOOL)configurePersistentStoreCoordinatorForURL:(NSURL *)url ofType:(NSString *)fileType modelConfiguration:(NSString *)configuration storeOptions:(NSDictionary *)storeOptions error:(NSError **)error
{
// No persistent store available yet
BOOL result = [super configurePersistentStoreCoordinatorForURL:url ofType:fileType modelConfiguration:configuration storeOptions:storeOptions error:error];
// Persistent store available, but how to determine if opening existing or saving a new document?
// Don't want to alter existing record unless saving a new document.
return result;
}