Sorting an Array error ?

[stephen]

Hello,

I'm trying to sort an array, code is as follows:

NSArray *sortedArray =[listArray sortedArrayUsingFunction:intSort context:nil];


NSInteger intSort(id num1, id num2, void *dummy)
{
    int v1 = [[num1 objectForKey:@"waypoint_order"] intValue];
    int v2 = [[num2 objectForKey:@"waypoint_order"] intValue];

    if (v1 < v2)
        return NSOrderedAscending;
    else if (v1 > v2)
        return NSOrderedDescending;
    else
        return NSOrderedSame;
}

But its crashing on line int v1 = [[num1 objectForKey:@"waypoint_order"] intValue]; with '-[NSManagedObject objectForKey:]: unrecognized selector sent to instance 0x7a6b7f0'.

What am I doing wrong, I must be leaving out some functionality.

Regards, Stephen

[smithdale87]

from the looks if the error, it looks like you are assuming that num1 and num2 are dictionaries, when in fact they are NSManagedObjects

Its hard to tell you more without knowing how you populated your listArray.

[stephen]

Originally Posted by smithdale87

from the looks if the error, it looks like you are assuming that num1 and num2 are dictionaries, when in fact they are NSManagedObjects

Its hard to tell you more without knowing how you populated your listArray.

listArray was populate by a NSFetchRequest:

NSFetchRequest *request = [[NSFetchRequest alloc] init];
	
		NSEntityDescription *entity = [NSEntityDescription entityForName:@"WayPoint" inManagedObjectContext:managedObjectContext];
		[request setEntity:entity];
		
		NSPredicate *predicate = [NSPredicate predicateWithFormat:@"waypoint_map_id contains[cd] %@", sharedMapID];
		[request setPredicate:predicate];
	
		NSError *error = nil;
		NSArray *results = [managedObjectContext executeFetchRequest:request error:&error];
	
		// Check for errors from the FetchRequest
		if (nil == results || nil != error)
			NSLog(@"Error getting results : %@", error);
	
		listArray = [results mutableCopy];
		[request release];

[stephen]

*Bump*

[stephen]

*bump*

[CambridgeCoders]

Hi,

Personally, I'm very wary of manipulating NSManagedObjects outside of CoreData's control. If I wanted a sorted array in this case, I would use a sort descriptor as part of the fetch request itself to sort the data. Would be neater, probably faster and avoids manually messing with NSManagedObjects.

See:

http://developer.apple.com/library/m.../fetching.html

Best regards,

[stephen]

Originally Posted by CambridgeCoders

Hi,

Personally, I'm very wary of manipulating NSManagedObjects outside of CoreData's control. If I wanted a sorted array in this case, I would use a sort descriptor as part of the fetch request itself to sort the data. Would be neater, probably faster and avoids manually messing with NSManagedObjects.

See:

Loading…

Best regards,

Thanks, I did try that but the values in CoreData are all strings. So this was causing a problem i.e. the results were 1,10,11,12.....2,20,21,22....etc.
Is there a way to sort a string as an integer via the NSFetchRequest.

[CambridgeCoders]

Hi,

I would do the following:

- Derive a class from NSManagedData to store your entities
- Add a virtual accessor to the class which returns the string values as integers

This is covered well here:

Introduction to Core Data, Part II

(scroll to "Virtual Accessors" part-way down the page).

Obvious question though - if the strings are just integers, can you not store them this way in CoreData itself?

Best regards,