如何在重新排序單元格後更改fetchresultcontroller數組中的對象的順序

Question

我有一個表視圖，並且我剛剛實現了一個類，該類幫助我重新排列單元格，就像表視圖委託中隨附的常規移動單元格方法。

現在我重新排序單元格後，我需要將保存單元格對象的數組更改爲新的順序......我該怎麼做？

這是我重新排序細胞的方法：

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

} 

我有一個coreDataStack類，它的所有的核心數據的東西護理（創建singelton），它看起來像這樣：

#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 

每當我新對象添加到核心數據我做這種方式：

- (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]; 

} 

表中的VIE當我獲取數據W I這樣來做：

- (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; 
} 

這是我fetchresultconroller /取表視圖控制器類的要求配置：

- (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; 

} 

我要完成什麼是每當一個用戶創建一個目標對象，它將會到達數組的末尾（所以它會像隊列一樣），並且如果用戶移動單元格，那麼我需要更改數據庫的數組順序...

活動細胞方法：

- (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); 
    } 
} 

日誌：

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，細胞的標籤，現在怪怪的，如果移動與標籤「一」與標籤「兩化」的單元格的指數的細胞，所以「one」的標籤正在變爲「two」。所以我認識到2個單元具有相同標籤的情況。

Answer 1

那麼最簡單的解決辦法是

1. 添加屬性您Target實體，說它Integer32類型的order。

創建並插入新的對象

每當創建新Target對象，首先使用sortDescriptor具有鍵@"order"和​​從數據庫讀取現有的對象。取出這個獲取數組的最後一個對象並檢查它的順序。現在在您的新Target對象中遞增訂單並將其插入數據庫。如果獲取的數組返回0個對象，則設置爲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

取使用上述的對象定義sortDescriptor。

從代碼兩者

- (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; 
    } 

重新排列細胞

現在，當重新排列在表格視圖細胞，同時，你只需要運行一個for循環並更新它們的順序。您只需要更新兩個indexPath之間的對象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：以上解決方案假定您有order從0

---

開始當你創建你需要實現NSFetchedResultsController委託方法添加插入新Target對象這些對象的相應行。由於我們已經定義了sortDescriptor，因此新行將被添加到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

如果您希望NSFetchResultsController獲取更改，您必須更改基礎數據模型以反映新的順序。

Answer 3

簡單的解決方案：Reffer Apple's Doc：

創建的NSMutableArray，以確定重新排序陣列。

步驟1：在頭文件或類文件中聲明NSMutableArray屬性@property (strong, nonatomic) NSMutableArray *arrayTag。

第2步：初始化在viewDidLoad

步驟3：在tableview委託方法添加該代碼

-(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 4

試試這個

-(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 5

如果我理解正確的您的問與答，你必須改變模型的模式。

A.首先，我的理解

你有一個項目列表。最後添加新項目。現在，您要讓用戶能夠以自定義的方式對項目進行重新排序。

B.你做

什麼其實你正在使用排序創建日期屬性。當然，你不能用這個重新排序，因爲這意味着改變創建日期。因此，使用創建日期的整個方法都會失敗：對於未由用戶更改的列表來說，這已經足夠了，但如果您有自定義的訂單，則不會。

C.你可以做

如果你有一個自定義的順序，你需要一個定製的屬性，以反映訂單。如果列表是實例對象的屬性，那麼可以使用NSOrderedSet和Core Data的有序關係來完成此操作。我不會因爲收益。但是，如果適合你，你可以做到。

否則你必須自己處理：

a。將屬性order添加到您的實體類型。

b。插入新對象時，請檢查現有列表的數量（取決於您如何保存它），並將該值設置爲新實例的order屬性。

c。提取時，使用該屬性進行排序。 d）。更改時，請更改源和目​​標之間的實例對象和所有實例對象的屬性。讓我來解釋一下：

我們有一個這樣的LIS：現在

name   order 
Amin   0 
Negm   1 
Awad   2 
Answer  3 

，例如，接聽移動向上從位置3（Negm提前）位置1：

name   order 
Amin   0 
Answer  3 
Negm   1 
Awad   2 

這意味着必須將移動對象（3）的順序屬性更改爲新目標（1），並且所有具有順序屬性> = 1至< 3的對象必須更改爲+1。 （和移動對象的順序屬性，也很明顯）

name   order 
Amin   0 
Answer  1 
Negm   2 
Awad   3 

代碼

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); 
} 

如果一個項目向下移動，你必須圓做同樣的其他方式。

---

如果您在iTunes中有不同的播放列表等獨特對象列表，則需要額外的實體類型而不是額外的屬性。讓我知道，我會從我的一本書中發佈代碼，包括移動一個有缺陷的項目列表。