Sort NSArray with custom objects - objective-c

Question

In my Xcode project I have the following classes:
Address
#interface LDAddress : NSObject{
NSString *street;
NSString *zip;
NSString *city;
float latitude;
float longitude;
}
#property (nonatomic, retain) NSString *street;
#property (nonatomic, retain) NSString *zip;
#property (nonatomic, retain) NSString *city;
#property (readwrite, assign, nonatomic) float latitude;
#property (readwrite, assign, nonatomic) float longitude;
#end
Location
#interface LDLocation : NSObject{
int locationId;
NSString *name;
LDAddress *address;
}
#property (readwrite, assign, nonatomic) int locationId;
#property (nonatomic, retain) LDAddress *address;
#property (nonatomic, retain) NSString *name;
#end
In an subclass of UITableViewController, there is a NSArray containing a lot of unsorted objects of LDLocations. Now, I want to sort the NSArray's objects ascending based on the property city of a LDAddress.
How can I sort the array using NSSortDescriptor?
I tried the following, but the app dumps when sorting the array.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"Address.city" ascending:YES];
[_locations sortedArrayUsingDescriptors:#[sortDescriptor]];

Answer 1

Try making the first key lowercase.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"address.city" ascending:YES];

Answer 2

You can also sort an array with blocks:
NSArray *sortedLocations = [_locations sortedArrayUsingComparator: ^(LDAddress *a1, LDAddress *a2) {
return [a1.city compare:a2.city];
}];

Answer 3

This will allow to sort with multiple types. Like we need to sort the Movie based on time and if the time is equal then need to sort by name.
NSArray *sortedArray = [childrenArray sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
NSNumber *first = [NSNumber numberWithLong:[(Movie*)a timeInMillis]];
NSNumber *second = [NSNumber numberWithLong:[(Movie*)b timeInMillis]];
NSComparisonResult result = [first compare:second];
if(result == NSOrderedSame){
result = [((NSString*)[(Movie*)a name] ) compare:((NSString*)[(Movie*)b name])];
}
return result;
}];

Answer 4

-(NSArray*)sortedWidgetList:(NSArray*)widgetList
{
NSSortDescriptor *firstDescriptor = [[NSSortDescriptor alloc] initWithKey:#"itemNum" ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObjects:firstDescriptor, nil];
NSArray *sortedArray = [widgetList sortedArrayUsingDescriptors:sortDescriptors];
return sortedArray;
}