Sorting an array of objects of elements by an attribute of elements

Question

I have a class. Lets call this class MyObject .

MyObject has a property called item .

If I create an instance of MyObject , instanceOfObject.item is a NSMetadataItem .

NSMetadataItem s have an attribute called NSMetadataItemFSNameKey .

I have an array of MyObjects and I want to sort that array by the attribute NSMetadataItemFSNameKey .

I have tried

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:NSMetadataItemFSNameKey
                                                               ascending:YES];

[array sortUsingDescriptors:@[sortDescriptor]];

but this obviously crashes because NSMetadataItemFSNameKey is not a key of array . Like I said, NSMetadataItemFSNameKey is an attribute of instanceOfObject.item .

Is there a way to do this using NSSortDescriptors ?

Answer 1

I'm not sure if this is what you are looking for, but I use this approach to sort an array of custom objects by a specified NSString property:

//Sort the list alphabetically by propertyName
NSArray* sortedArray;
sortedArray = [startingArray sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
    NSString* first = [(WSCustomObject*)a propertyName];
    NSString* second = [(WSCustomObject*)b propertyName];
    return [first compare:second];
}];

You just need to make sure you #import the custom class header where you are making this call. You can also compare other data types using slight modifications to this approach. If you have a specific data type in mind other than NSString let me know what it is and I can help you modify this one (or I probably already have an example of it floating around I can show you).