I have a NSArray of objects. Those objects have an int attribute called "distance". I would like to sort my array by distance.
Could someone please tell me how to do that ? I can't understand how the sortUsingSelector or sortUsingDescriptor methods are working...
Thanks
I assume you're using an NSMutableArray, because an NSArray is immutable.
When you sort something, you want the end result to be arranged as
x1 <= x2 <= x3 <= x4 <= ... <= xN
How to define this <=? There are 3 solutions in ObjC.
-sortUsingSelector:[arr sortUsingSelector:@selector(foo:)] means that its elements will be compared as*
x <= y is equivalent to [x foo:y] <= 0
For example, to sort a list of strings case-insensitively, you use [arr sortUsingSelector:@selector(caseInsensitiveCompare:)].
-sortUsingFunction:context:This is similar to -sortUsingSelector:, but it uses a function pointer as input. [arr sortUsingFunction:funcptr context:ctx] means that its elements will be compared as
x <= y is equivalent to funcptr(x, y, ctx) <= 0
-sortUsingDescriptors:This is the most complicated one. It takes a list of NSSortDescriptors which describe the expected order of the properties. One basic example:
NSSortDescriptor* desc = [[NSSortDescriptor alloc] initWithKey:@"distance" ascending:YES];
[arr sortUsingDescriptors:[NSArray arrayWithObject:desc]];
[desc release];
the descriptor tells the sort routine to "sort by the key distance in ascending order".
Suppose there are 2 keys, integers x ascending then and strings y descending, then you may write
NSSortDescriptor* dx = [[NSSortDescriptor alloc] initWithKey:@"x" ascending:YES];
NSSortDescriptor* dy = [[NSSortDescriptor alloc] initWithKey:@"y" ascending:NO selector:@selector(caseInsensitiveCompare:)];
[arr sortUsingDescriptors:[NSArray arrayWithObjects:x, y, nil]];
[dx release];
[dy release];
and so on.
Note: * Actually you should only return -1, 0 or 1.
NSOrderedDescending, NSOrderedSame, or NSOrderedAscending.
Finnaly I found out how to do that :
after @implementation :
static NSInteger sort(Myclass *obj1, Myclass *obj2, void *context) {
if(obj1.distance < obj2.distance)
return NSOrderedAscending;
else if(obj1.distance > obj2.distance)
return NSOrderedDescending;
else
return NSOrderedSame;
Then wherever you need to sort your NSArray :
NSArray *sortedArray = [unsortedArray sortedArrayUsingFunction:sort context:NULL];