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Asked: 2026-06-02T03:25:07+00:00

I’m currently trying to teach myself Objective-C and was playing around with an exercise

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I’m currently trying to teach myself Objective-C and was playing around with an exercise where I needed to sort an array.

I managed to complete it using the following code:

NSSortDescriptor * newSortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"title" ascending:TRUE];
NSArray *sortDescriptors = [NSArray arrayWithObject:newSortDescriptor];
[self.theBookStore sortUsingDescriptors:sortDescriptors];

My question is about what is actually happening here. I don’t really understand exactly what I’ve done.

Line 1: I understand here I’ve created a new object that has a descriptor. This has two parameters, the column I want to sort on and that it is ascending.

Line 2: This is the line I’m confused about. Why do I need an array of sort descriptors? When I read this code I suspect it creates an array with only one row is that correct?

Line 3: I understand that this is calling the sortUsingDescriptors method but again, my confusion is why this function expects an array.

I’ve read the documentation but I’m really looking for a simple explanation.

Any help is much appreciated

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1 Answer

  1. Editorial Team

    • Line 1: .. yes your right. You are creating a custom object called NSSortDescriptor. That object defines a attribute to sort after. You did enter “title”. So the objects in your array-to-sort will be sorted after that property (yourObject.title “kind-of”).

    • Line 2: Because the sorting method (sortUsingDescriptors) always needs a array, you need to create a NSArray with only one object. Okay, … looks kind of stupid. But makes absolute sense. Lets say you would like to sort after two criteria (lets say “title”, then “city”).

    • Line 3: Yes heres must be a array because of sorting after more then one criteria.

    And always keep the memory clean:
    On line 1 you did allocate/init a NSSortDescriptor.
    So clean up after using it (if you are not using ARC).
    So add a line:

    [newSortDescriptor release];
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