我有一个方法用于保存并将表格视图中的单元格移动到不同的索引，如下所示：
- (void)moveTableView:(FMMoveTableView *)tableView moveRowFromIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath {
NSArray *allObjects = [self.fetchedResultController fetchedObjects];
//array to hold the new order
NSMutableArray * arrayCorectOrder = [NSMutableArray new];
//the target object that is in the index we are moving from
Target *target = [self.fetchedResultController objectAtIndexPath:fromIndexPath];
}
我有一个coreDataStack类来处理所有核心数据（创建一个singelton），它看起来像这样：
#import "CoreDataStack.h"
@implementation CoreDataStack
#pragma mark - Core Data stack
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
+ (instancetype)defaultStack {
static CoreDataStack *defaultStack;
static dispatch_once_t onceTocken;
dispatch_once (&onceTocken, ^{
defaultStack = [[self alloc] init];
});
return defaultStack;
}
- (NSURL *)applicationDocumentsDirectory {
// The directory the application uses to store the Core Data store file. This code uses a directory named "digitalCrown.Lister" in the application's documents directory.
return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}
- (NSManagedObjectModel *)managedObjectModel {
// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
if (_managedObjectModel != nil) {
return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Lister" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
// The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it.
if (_persistentStoreCoordinator != nil) {
return _persistentStoreCoordinator;
}
// Create the coordinator and store
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Lister.sqlite"];
NSError *error = nil;
NSString *failureReason = @"There was an error creating or loading the application's saved data.";
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
// Report any error we got.
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
dict[NSLocalizedFailureReasonErrorKey] = failureReason;
dict[NSUnderlyingErrorKey] = error;
error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
// Replace this with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return _persistentStoreCoordinator;
}
- (NSManagedObjectContext *)managedObjectContext {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (!coordinator) {
return nil;
}
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
return _managedObjectContext;
}
#pragma mark - Core Data Saving support
- (void)saveContext {
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
NSError *error = nil;
if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
}
@end
每当我向核心数据添加新对象时，我就这样做：
- (void)insertTeget {
CoreDataStack *stack = [CoreDataStack defaultStack];
Target *target = [NSEntityDescription insertNewObjectForEntityForName:@"Target" inManagedObjectContext:stack.managedObjectContext];
if (self.myTextView.text != nil) {
target.body = self.myTextView.text;
target.time = [NSDate date];
}
[stack saveContext];
}
在表格视图中，当我提取数据时，我这样做：
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *cellIdentifier = @"StackTableViewCell";
Target *target = [self.fetchedResultController objectAtIndexPath:indexPath];
StackTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (!cell)
{
NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:@"StackTableViewCell" owner:self options:nil];
cell = [topLevelObjects objectAtIndex:0];
}
cell.cellLabel.text = target.body;
cell.cellLabel.font = [UIFont fontWithName:@"Candara-Bold" size:20];
cell.showsReorderControl = YES;
// Configure the cell...
return cell;
}
这是我在表视图控制器类中的fetchresultconroller / fetch请求配置：
- (NSFetchRequest *)targetsFetchRequest {
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Target"];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"time" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
return fetchRequest;
}
- (NSFetchedResultsController *)fetchedResultController {
if (_fetchedResultController != nil) {
return _fetchedResultController;
}
CoreDataStack *stack = [CoreDataStack defaultStack];
NSFetchRequest *fetchRequest = [self targetsFetchRequest];
_fetchedResultController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:stack.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
_fetchedResultController.delegate = self;
return _fetchedResultController;
}
现在我想知道订单是否已更改，所以我需要更改数据库中的订单......
我该怎么做？
谢谢！
答案 0 :(得分：0)
我建议您考虑向您的实体Target添加其他属性，也许称之为“sortOrder”？
获取结果时，请考虑按sortOrder进行排序。
要使其工作，您需要在创建每个实体时设置sortOrder值。这应该相对简单...在创建实体之前完成fetchedResults的计数，假设您的下一个sortOrder值将等于计数值加1。
在tableview中移动行时，可以使用代码重新分配受影响单元格的sortOrder值，使其等于indexPath.row属性。
保存后，您的新排序顺序应该会保留。
答案 1 :(得分：0)
根据我的评论，获取的结果控制器基于底层提取的排序顺序为每个对象建立indexPath - 在您的情况下为time。如果您希望用户能够覆盖此行，并对行重新排序，则更改FRC以使用不同的排序顺序。向您的实体添加一个名为sortTime的新属性（日期类型），并修改targetsFetchRequest方法以使用sortTime作为排序键。
每当您添加新的Target时，请同时设置sortTime。在重新排序行时，设置sortTime的值以确保FRC将Target放在新的indexPath上。像这样：
-(void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath {
Target *targetToMove = [self.fetchedResultsController objectAtIndexPath:sourceIndexPath];
if (destinationIndexPath.row == 0) {
// to move to row 0, the new sortTime can be any value
// that is less than the sortTime of the Target currently at
// row 0
Target *targetAtRow0 = [self.fetchedResultsController objectAtIndexPath:destinationIndexPath];
targetToMove.sortTime = [targetAtRow0.sortTime dateByAddingTimeInterval:-1];
} else {
// for any other row, set the sortTime to be half way
// between the sortTime for the row before the new position
// and the sortTime for the row at the new position
Target *targetBefore = [self.fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:(destinationIndexPath.row-1) inSection:destinationIndexPath.section]];
Target *targetAfter = [self.fetchedResultsController objectAtIndexPath:destinationIndexPath];
double lowerTimeInterval = [targetBefore.sortTime timeIntervalSinceReferenceDate];
double upperTimeInterval = [targetAfter.sortTime timeIntervalSinceReferenceDate];
double newInterval = (lowerTimeInterval + upperTimeInterval)/2;
NSDate *newSortTime = [NSDate dateWithTimeIntervalSinceReferenceDate:newInterval];
targetToMove.sortTime = newSortTime;
}
NSError *error;
if (![self.managedObjectContext save:&error]) {
NSLog(@"SaveContext: error %@, %@", error, [error userInfo]);
abort();
}
}
这应该触发您的FRC委托方法来执行必要的表视图更新。