如何在重新排序单元格后更改fetchresultcontroller数组中对象的顺序

Question

我有一个表视图,我刚刚实现了一个类,可以帮助我重新排序单元格,就像表视图委托附带的常规移动单元格方法一样.

现在我重新排序单元格后,我需要将保存单元格对象的数组更改为新顺序...我该怎么做？

这是我重新排序单元格的方法:

- (void)moveTableView:(FMMoveTableView *)tableView moveRowFromIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath { NSArray 

}

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,我都是这样做的:

- (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,当我获取数据时,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;

}

我想要实现的是,每当用户创建一个目标对象时,它将转到数组的末尾(因此它将像一个队列),如果用户移动单元格,那么我需要更改数组的顺序数据库...

移动单元法:

- (void)moveTableView:(FMMoveTableView *)tableView moveRowFromIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath {

    int start = 0;
    int end = 0;
    if (fromIndexPath.row > toIndexPath.row) {
        start = (int)fromIndexPath.row;
        end = (int)toIndexPath.row;
    } else {
        start = (int)toIndexPath.row;
        end = (int)fromIndexPath.row;
    }

    for (int i = start; i <= end; ++i) {
        Target *target = [self.fetchedResultController objectAtIndexPath:[NSIndexPath indexPathForRow:i inSection:0]];
        [target setOrder:@(i)];
    }

    [[CoreDataStack defaultStack] saveContext];


    // a test to see if the order is changed
    [self.fetchedResultController performFetch:nil];

    NSArray *arr = [self.fetchedResultController fetchedObjects];
    for (int i=0; i<arr.count; i++)  {
        Target *ta = [arr objectAtIndex:i];
        NSLog(@"%@",ta.body);
    }
}

日志:

2015-04-14 10:29:13.405 Lister[3163:477453] One
2015-04-14 10:29:13.406 Lister[3163:477453] Two
2015-04-14 10:29:13.406 Lister[3163:477453] Three
2015-04-14 10:29:13.407 Lister[3163:477453] Four
2015-04-14 10:29:13.407 Lister[3163:477453] Five
2015-04-14 10:29:21.070 Lister[3163:477453] 

2015-04-14 10:29:21.071 Lister[3163:477453] One
2015-04-14 10:29:21.071 Lister[3163:477453] Two
2015-04-14 10:29:21.071 Lister[3163:477453] Three
2015-04-14 10:29:21.072 Lister[3163:477453] Four
2015-04-14 10:29:21.072 Lister[3163:477453] Five
2015-04-14 10:29:25.037 Lister[3163:477453] 

2015-04-14 10:29:25.039 Lister[3163:477453] One
2015-04-14 10:29:25.039 Lister[3163:477453] Two
2015-04-14 10:29:25.040 Lister[3163:477453] Three
2015-04-14 10:29:25.040 Lister[3163:477453] Four
2015-04-14 10:29:25.041 Lister[3163:477453] Five

此外,如果将带有标签"one"的单元格移动到标签为"two"的单元格的索引,则单元格的标签现在表现得很奇怪,因此"one"的标签变为"two".所以我得到了2个单元格具有相同标签的情况.

Answer 1

那么最简单的解决方案就是

1. 向您的Target实体添加属性,比如order类型Integer32.

创建和插入新对象

2. 无论何时创建新Target对象,首先使用sortDescriptor具有键@"order"和的数据库从数据库中获取现有对象ascending=YES.获取此获取数组的最后一个对象并检查其顺序.现在,在新Target对象中递增顺序并将其插入数据库.如果fetched数组返回0个对象,则设置order=@(0).

   - (void)insertTeget {
   
       CoreDataStack *stack = [CoreDataStack defaultStack];
   
       //Fetching objects from database
       NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Target"];
       NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"order" ascending:YES];
       [fetchRequest setSortDescriptors:@[sortDescriptor]];
       NSArray *existingObjects = [stack.managedObjectContext executeFetchRequest:fetchRequest error:nil];
   
       //Creating new object
       Target *target = [NSEntityDescription insertNewObjectForEntityForName:@"Target" inManagedObjectContext:stack.managedObjectContext];
       if (self.myTextView.text != nil) {
           target.body = self.myTextView.text;
           target.order = @([(Target *)existingObjects.lastObject order].integerValue + 1);
       }
   
       [stack saveContext];
   }
   

NSFetchedResultsController

3. 使用上面定义的方法获取对象sortDescriptor.

取自你的代码

    - (NSFetchRequest *)targetsFetchRequest {

        NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Target"];
        NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"order" 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;
    }

重新排列细胞

4. 现在,当您在表视图中重新排列单元格时,您只需运行for循环并更新其顺序.您只需要更新order两个indexPath之间的对象.

   - (void)moveTableView:(FMMoveTableView *)tableView moveRowFromIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath {  
   
       int start = 0;
       int end = 0;
       if (fromIndexPath.row > toIndexPath.row) {
           start = fromIndexPath.row;
           end = toIndexPath.row;
       } else {
           start = toIndexPath.row;
           end = fromIndexPath.row;
       }
   
       for (int i = start; i <= end; ++i) {
           Target *target = [self.fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:i inSection:0]];
           [target setOrder:@(i)];
       }
   
       [[CoreDataStack defaultStack] saveContext];
   }
   

注意:上述解决方案假设您order从0开始.

在创建和插入新Target对象时,需要实现NSFetchedResultsController委托方法以为这些对象添加相应的行.由于我们已经定义sortDescriptor,新行将添加到结尾tableView.

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView beginUpdates];
}


- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
    atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex]
                            withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}


- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
    atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
    newIndexPath:(NSIndexPath *)newIndexPath {

    UITableView *tableView = self.tableView;

    switch(type) {

        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                       withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                       withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                       withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}


- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView endUpdates];
}