Question

I couldn’t find out why sorting NSArray of DBMetadata (NSObject) doesn’t work. Here is my code. What is wrong? I even tried adding a category to add compare: but it doesn’t work.

- (void)restClient:(DBRestClient *)client loadedMetadata:(DBMetadata *)metadata {
    if (metadata.isDirectory) {
        NSLog(@"Folder '%@' contains:", metadata.path);
        for (DBMetadata *file in metadata.contents) {
            NSLog(@"\t%@  is directory? %d", file.filename, file.isDirectory);
            if (file.isDirectory) {
                [self.availableBackups addObject:file];
                DLog(@"llastModifiedDate %@", file.lastModifiedDate);
            }
        }
    }
//    NSLog(@"before sorting: %@", self.availableBackups); //lastModifiedDate //filename

    NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"lastModifiedDate"  ascending:YES selector:@selector(compare:)];
    [self.availableBackups sortedArrayUsingDescriptors:[NSArray arrayWithObjects:descriptor,nil]];

//    NSLog(@"after sorting: %@", self.availableBackups);
}

self.availableBackups is NSMutableArray

@property (nonatomic, retain) NSMutableArray *availableBackups;

Dropbox – DBMetadata.h

Commented NSLog just print the address of obj, you can see the output of address is still the same after sorting regardless of YES or NO for ascending:

output

2013-01-31 17:20:12.423 Dropbox[7366:c07] before sorting: (
    "<DBMetadata: 0x6bbf010>",
    "<DBMetadata: 0x6bbfb50>",
    "<DBMetadata: 0x6bc1660>",
    "<DBMetadata: 0x6bc17b0>",
    "<DBMetadata: 0x6bc14f0>",
    "<DBMetadata: 0x6bc0dd0>",
    "<DBMetadata: 0x6bc1de0>"
)
2013-01-31 17:20:12.424 Dropbox[7366:c07] after sorting: (
    "<DBMetadata: 0x6bbf010>",
    "<DBMetadata: 0x6bbfb50>",
    "<DBMetadata: 0x6bc1660>",
    "<DBMetadata: 0x6bc17b0>",
    "<DBMetadata: 0x6bc14f0>",
    "<DBMetadata: 0x6bc0dd0>",
    "<DBMetadata: 0x6bc1de0>"
)

with ascending NO

Last Modified file at 0: 2013-01-30 08:00:22 +0000
Last Modified file at 1: 2013-01-30 08:02:54 +0000
Last Modified file at 2: 2013-01-31 09:08:26 +0000
Last Modified file at 3: 2013-01-31 09:14:55 +0000
Last Modified file at 4: 2013-01-31 09:14:08 +0000
Last Modified file at 5: 2013-01-31 09:16:43 +0000
Last Modified file at 6: 2013-01-31 10:36:13 +0000

Answer 1

sortedArrayUsingDescriptors: returns an array, it does not modify the array you’re applying it on. If you need to use NSArray, try:

self.availableBackups = [self.availableBackups sortedArrayUsingDescriptors:[NSArray arrayWithObjects:descriptor,nil]];    

If you can use NSMutableArray, you could use:

[self.availableBackups sortUsingDescriptors:[NSArray arrayWithObjects:descriptor,nil]];