How to sort two different objects in an NSArray?

Question

In my NSArray, I have two types of objects, let's say objects of class A and class B. I want to sort these objects, by comparing "startingDate" property of class A to "endingDate" property of class B. And I don't know how to make a comparison based on two different properties of different classes.

What's the best way to do this?

score 2 · Accepted Answer · edited May 23 '17 at 12:03

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Blocks are what you want, take a look at this question: How to sort an NSMutableArray with custom objects in it?

In the blocks example on that question, just have class A use startingDate and class B use ending date.

edited May 23 '17 at 12:03

Community

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answered Feb 10 '12 at 15:32

rooftop

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Yes I saw that, but all the block methods were comparing the same type of objects. I mean the block's arguments are id obj1 and id obj2, but then they're cast to the same classes. Now that I have two different types of objects, won't casting be a problem? How will I know which argument to cast to my first class? – aslı Feb 10 '12 at 17:08
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You could check to see what kind of class obj1 and obj2 are by using [[(obj1/obj2) class] isSubclassofClass: [TargetClass class]] and then dealing with appropriately. – SushiGrass Jacob Feb 10 '12 at 17:25
Of course, but it's kind of messy to do so. I'll go that way if there aren't any better options though, thanks. – aslı Feb 10 '12 at 17:31
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@Jacob use `isKindOfClass` since both objects are probably subclasses of `NSObject`, or they could be subclasses of some other higher level object. – Jack Lawrence Feb 16 '12 at 22:59

score 0 · Answer 2 · answered Feb 16 '12 at 22:57

I would recommend an if/else block and the use of the statement

[myObject isKindOfClass:[ClassA class]]

Which returns a BOOL

If you'd rather (or in conjunction), Apple recommends using

[myObject respondsToSelector:@selector(startingDate)]

Which also returns a BOOL.

Blocks aren't really relevant in this situation; You could use this design pattern inside a plain method implementation, blocks, a for/while loop, or anywhere else.

How to sort two different objects in an NSArray?

2 Answers2