Objective-C - Directly call method from array of objects

Question

I'm new to Objective C, and I'm trying to call a method on an array (NSArray) of objects directly like this:

[[myPeople objectAtIndex: 0] setName: @"Shane"];

But this doesn't seem to work, and returns a warning saying "Multiple methods named 'setName' found"

I can successfully perform the operation in this manner:

Person* person = [myPeople objectAtIndex: 0];
[person setName: @"Shane"];

Is my syntax simply incorrect in the first case, or should the second piece of code be used? Or is there a better way that I'm not aware of?

Thanks, any help is greatly appreciated

Note that if you have two declarations of setName: where the argument or return type are different, then you are writing code against the recommended conventions of the system. Rename one of the methods. — bbum
– bbum, Commented Sep 22, 2011 at 5:52

Julian · Accepted Answer · 2016-04-05 09:10:19Z

8

You can do it to all objects in the array like this:

[myPeople makeObjectsPerformSelector:@selector(setName:) withObject:@"Shane"];

edited Apr 5, 2016 at 9:10

Julian

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answered Sep 22, 2011 at 7:20

Michael Frederick

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Comments

Adam Rosenfield · Accepted Answer · 2011-09-22 04:13:03Z

The first syntax is correct and will work correctly, despite the warning. The compiler is warning you because it can't verify the type of object that you're calling setName: on.

The method objectAtIndex: of the NSArray class returns the type id, which is a generic pointer to an Objective-C object of unknown type. So, when you call setName: on the id that is returned, the compiler doesn't know what the actual class of the object is. In your code, there are multiple classes that define the setName: method (possibly as a synthesized setter for a property named name), so it issues a warning.

The second code snippet compiles without warning because the id type can be implicitly cast to any other Objective-C pointer type. When you say Person* person = [myPeople objectAtIndex: 0];, you're taking the id returned by objectAtIndex: and casting it (implicitly) to Person*. Then, when you call setName: on that Person, the compiler knows what type you have, so it can verify that the class Person does in fact implement the setName: method.

The Lazy Coder · Accepted Answer · 2011-09-22 04:19:51Z

3

if you want to bypass the compiler warning. There are two other approaches then the one you demonstrated.

you can call performSelector:withObject on it.

[[myPeople objectAtIndex: 0] performSelector:@selector(setName:) withObject: @"Shane"];

usually with this method, you want to make sure it responds to the selector.

if ([[myPeople objectAtIndex: 0] respondsToSelector:@selector(setName:)])

another option is to cast the result

[(Person*)[myPeople objectAtIndex: 0] setName: @"Shane"];

these should eliminate the compiler warnings.

answered Sep 22, 2011 at 4:19

The Lazy Coder

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