ReorderableArrayControllerAndCoreData

I’m having an interesting problem. I have a basic CoreData app that uses an NSArrayController to manage some data in a table view. I wanted to add reordering of the data, so I subclassed NSArrayController, and implemented some table view data source methods, hooked them up… and it sort of works. When I drag reorder a row, I can see it appear where it should be for a second - then it’s deleted, instantly! I’ve tried this both with my code and a modified version of stuff on mmalcom’s site. At first I figured it was just a problem with my app, so I made a simple test project:

New CoreData app, add an entity called “Test”, with a string attribute for “name.” Insert an array controller, an add button, a table view. Hook them up. Insert my drag reorder stuff, reorder, row appears there for a split second, then the object is removed from the store. My code is below – any leads would be very much appreciated.

#import “DragReorderingArrayController.h”

NSString *MovedRowsType = @”MOVED_ROWS_TYPE”;

@implementation DragReorderingArrayController

(void)awakeFromNib { [tableView registerForDraggedTypes: [NSArray arrayWithObjects:MovedRowsType, nil]]; [tableView setAllowsMultipleSelection:NO]; [super awakeFromNib]; }
(BOOL)tableView:(NSTableView )tv writeRows:(NSArray)rows toPasteboard:(NSPasteboard*)pboard { NSArray *typesArray = [NSArray arrayWithObject:MovedRowsType];

[pboard declareTypes:typesArray owner:self]; [pboard setPropertyList:rows forType:MovedRowsType];

return YES; }
(NSDragOperation)tableView:(NSTableView*)tv validateDrop:(id )info proposedRow:(int)row proposedDropOperation:(NSTableViewDropOperation)op {

NSDragOperation dragOp = ([info draggingSource] == tableView) ? NSDragOperationMove : NSDragOperationCopy;

[tv setDropRow:row dropOperation:NSTableViewDropAbove];

return dragOp; }

(BOOL)tableView:(NSTableView*)tv acceptDrop:(id )info row:(int)row dropOperation:(NSTableViewDropOperation)op { if (row < 0) row = 0;

if ([info draggingSource] == tableView) { NSArray *rows = info draggingPasteboard] propertyListForType:[[MovedRowsType]; int theRow = rows objectAtIndex:0]intValue];

  id object = [[[self arrangedObjects]objectAtIndex:theRow]retain];
	
  if (row != theRow+1 && row != theRow)
  {
      if (row < theRow)
          [self removeObjectAtArrangedObjectIndex:theRow];
		
      if (row <= [[self arrangedObjects] count])
          [self insertObject:object atArrangedObjectIndex:row];
      else
          [self addObject:object];
		
      if (row > theRow)
          [self removeObjectAtArrangedObjectIndex:theRow];
		
      [object release];
		
      return YES;
  }
  return NO;   }

return NO; }

@end

Core Data uses [[NSSet and NSMutableSet, which do not support ordered indexing. There is no way to ensure data is stored or retrieved in order. The way around this is to add a property like -orderIndex to your entity and change that when rows are dragged. In other words, if #5 is moved to #3, everything from #3 and up is renumbered in the dragged order. Upon retrieval, you sort by the -orderIndex to maintain the dragged order.

Ah, well thanks for the tip.

CocoaDev