Core Data Notes
两篇很不错的 Core Data Tutorial, Getting Started,How to use NSFetchedResultsController。
NSPersistentStoreCoordinator 是持久化存储, NSManagedObjectModel 指明存储数据结构和关系,NSManagedObjectContext 来读取、存储操作。
- (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;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"CDTest" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
if (_persistentStoreCoordinator != nil) {
return _persistentStoreCoordinator;
}
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"CDTest.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]);
}
return _persistentStoreCoordinator;
}
新增数据:
Person *person = [NSEntityDescription insertNewObjectForEntityForName:@"Person"
inManagedObjectContext:_managedObjectContext];
person.name = @"fannheyward";
person.age = [NSNumber numberWithInt:25];
[_managedObjectContext save:NULL];
通过 NSFetchRequest 查找,配合 NSPredicate 对数据进行过滤判断:
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Person"];
request.predicate = [NSPredicate predicateWithFormat:@"age == %@", age];;
NSArray *arr = [_managedObjectContext executeFetchRequest:request error:NULL];
for (NSManagedObject *obj in arr) {
//...
}
NSFetchedResultsController 和 UITableView 做了很好的整合,可以根据 tableView 位置进行动态查询取数据。比如一共 100 个 cell,传统方式需要一次性全部拿到 DataSource 数据到内存,数据量过大的话会占用不少内存;用 NSFetchedResultsController 可以设置一次取数据的大小,然后根据滑动位置动态读取数据。
- (NSFetchedResultsController *)fetchController
{
if (_fetchController != nil) {
return _fetchController;
}
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Place"
inManagedObjectContext:_managedContext];
request.entity = entity;
request.fetchBatchSize = 15;
NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:NO];
request.sortDescriptors = [NSArray arrayWithObject:sort];
_fetchController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
managedObjectContext:_managedContext
sectionNameKeyPath:nil
cacheName:@"Place"];
_fetchController.delegate = self;
NSError *error = nil;
if (![_fetchController performFetch:&error]) {
DLog(@"fetch error: %@", [error description]);
abort();
}
return _fetchController;
}
和 UITableView 的整合:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
id <NSFetchedResultsSectionInfo> info = [[_fetchController sections] objectAtIndex:section];
return [info numberOfObjects];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
//...
Place *place = [_fetchController objectAtIndexPath:indexPath];
return cell;
}
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