重新排序单元格后如何更改获取结果控制器数组中对象的顺序

Question

我有一个表格视图，我刚刚实现了一个可以帮助我重新排列单元格的类，就像表格视图委托附带的常规移动单元格方法一样。

现在，在对单元格重新排序后，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？

这是我对单元格重新排序的方法：

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

}

我有一个 coreDataStack 类来处理所有的核心数据（创建一个单例），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，我都会这样做：

- (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，当我获取数据时，我是这样做的：

- (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;

}

我想要完成的是，每当用户创建一个目标对象时，它都会走到数组的末尾（所以它就像一个队列），如果用户移动单元格，那么我需要更改数据库数组...

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

另外，单元格的标签现在表现得很奇怪，如果将带有标签“一”的单元格移动到带有标签“二”的单元格的索引，那么“一”的标签将变为“二” .所以我得到了2个单元格具有相同标签的情况。

Answer 1

最简单的解决方案是

1. 为您的Target 实体添加一个属性，例如order 类型为Integer32。

创建和插入新对象

1. 每当您创建一个新的Target 对象时，首先使用sortDescriptor 从数据库中获取现有对象，键为@"order" 和ascending=YES。取出这个获取数组的最后一个对象并检查它的顺序。现在在您的新Target 对象中增加订单并将其插入数据库。如果获取的数组返回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

1. 使用上面定义的sortDescriptor获取对象。

取自您的代码

    - (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;
    }

重新排列单元格

4. 现在，当您在表格视图中重新排列单元格时，您只需要运行一个 for 循环并更新它们的顺序。您只需更新两个 indexPath 之间的对象的order。

   - (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：上面的解决方案假设你有order从0开始。

---

当您创建和插入新的Target 对象时，您需要实现NSFetchedResultsController 委托方法来为这些对象添加相应的行。由于我们已经定义了sortDescriptor，所以新的行将添加到tableView的末尾。

- (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];
}

Answer 2

简单解决方案： Reffer Apple's Doc:

创建一个 NSMutableArray 来识别重新排序的数组。

第 1 步：在头文件或类文件中声明 NSMutableArray 属性 @property (strong, nonatomic) NSMutableArray *arrayTag。

第二步：在viewDidLoad中初始化

第 3 步：将此代码添加到 tableview 委托方法中

-(void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath
{
    NSString *stringToMove = [arrayTag objectAtIndex:sourceIndexPath.row];
    [arrayTag removeObjectAtIndex:sourceIndexPath.row];
    [arrayTag insertObject:stringToMove atIndex:destinationIndexPath.row];
}

Answer 3

试试这个

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

    NSString *str1 =  [[yourArray  objectAtIndex:fromIndexPath.row] copy];
    NSString *str2 =  [[yourArray  objectAtIndex:toIndexPath.row] copy];

    [yourArray replaceObjectAtIndex:fromIndexPath.row withObject:str2];
    [yourArray replaceObjectAtIndex:toIndexPath.row withObject:str1];

    [tableView reloadData];
}

Answer 4

如果我正确理解了您的 Q，您必须更改模型的架构。

A.一、我的理解

您有一个项目列表。最后添加新项目。现在您想让用户能够以自定义方式重新排序项目。

B.你做什么

实际上，您正在使用创建日期属性进行排序。当然，您不能将其用于重新排序，因为这将意味着更改创建日期。因此，使用创建日期的整个方法都失败了：对于不由用户更改的列表来说已经足够了，但如果您有自定义订单，则不是。

C.你能做什么

如果您有自定义订单，则需要自定义属性来反映订单。如果列表是实例对象的属性，您可以使用NSOrderedSet 和Core Data 的有序关系来执行此操作。我不会因为有回报。但是，如果对您有用，您可以这样做。

否则你必须自己处理：

一个。将属性 order 添加到您的实体类型。

b.插入新对象时，检查现有列表的计数（取决于您持有它的方式）并将值设置为新实例的 order 属性。

c。获取时，使用该属性进行排序。

d。更改时，更改实例对象的属性以及源和目标之间的所有实例对象的属性。让我解释一下：

我们有一个这样的列表：

name          order
Amin          0
Negm          1
Awad          2
Answer        3

现在，例如，Answer 向上从位置 3 移动到位置 1（在 Negm 之前）：

name          order
Amin          0
Answer        3
Negm          1
Awad          2

这意味着移动对象 (3) 的 order 属性必须更改为新的目标 (1)，并且所有具有 >=1 到

name          order
Amin          0
Answer        1
Negm          2
Awad          3

在代码中

NSUInteger oldIndex = …; // 3
NSUInteger newIndex = …; // 1

movedObject.order = newIndex;

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Target"];
NSPredicate *betweenPredicate = [NSPredicate predicateWithFormat:@"order >= %ld AND order < %ld", newIndex, oldIndex];
NSArray *objectsToChange = [context executeFetchRequest:request error:NULL];

for( Target *target in objectsToChange )
{
  target.order = @([target.order unsignedIntegerValue] + 1);
}

如果一个项目被向下移动，你必须反过来做同样的事情。

---

如果您有不同的唯一对象列表，例如 iTunes 中的播放列表，您需要一个额外的实体类型而不是一个额外的属性。让我知道，我将发布我的一本书中的代码，包括移动有间隙的项目列表。

Answer 5

如果您希望 NSFetchResultsController 接受更改，则必须更改底层数据模型以反映新订单。