Expected method to read array element not found on object of type 'id'

Question

I want to update XCode version.

But while updating I receive several compiler errors. The are the same as this:

id<MyProtocol> objectToDelete = group[index.unsignedIntegerValue];

Expected method to read array element not found on object of type 'id'

id<MyProtocol> _Nonnull group

@protocol MyProtocol <NSObject>

@property (copy, nonatomic) NSString* name;
@property (copy, nonatomic) NSString* id;
@property (copy, nonatomic) NSString* internalType;
@property (strong, nonatomic) NSMutableArray<id<SomeAnotherProtocol>>* objects;

- (instancetype)initWithObject:(MyProtocol*)object;
// Search
- (BOOL)isContainsObjectWithID:(NSString*)myID;
- (NSUInteger)indexForObjectID:(NSString*)myID;
- (id<SomeAnotherProtocol>)objectWithID:(NSString*)myID;
- (NSString*)groupID;

@end

This error appears only on XCode 9.3 version.

Does id<MyProtocol> objectToDelete = ((NSArray *) group)[index.unsignedIntegerValue]; the only solution?

`id objectToDelete = [group objectAtIndex:index.unsignedIntegerValue];` might do the trick too. — Larme, Apr 03 '18 at 10:06
@Larme `No known instance method for selector 'objectAtIndex:'` — Vyacheslav, Apr 03 '18 at 10:07

score 2 · Accepted Answer · answered Apr 03 '18 at 19:58

First, I'm assuming that group is not actually an NSArray, but is in fact:

id<MyProtocol> _Nonnull group

This says that group is "some object that conforms to MyProtocol". Nothing in MyProtocol says that this object can be subscripted. If you want it to be subscriptable by indexes, then you need to say this in the protocol:

@protocol MyProtocol <NSObject>
- (id<MyProtocol>)objectAtIndexedSubscript:(NSUInteger)idx;
...

And you of course need to implement objectAtIndexedSubscript: in anything that conforms (but this seems to already be the case, since it works when you cast it).

score -1 · Answer 2 · answered Apr 03 '18 at 19:23

-1

try this one: [group objectAtIndexedSubscript:idx]

answered Apr 03 '18 at 19:23

Юрий Копачевский

1
1

Care to add any information on why the poster should try that one? – Shane Ray Apr 03 '18 at 19:49
because his project worked with xcode 9.2, but failed with xcode 9.3. So if `group[...]` works, and `objectAtIndex:index` failes, I suggest, that somewhere object `group` implements `objectAtIndexedSubscript:` method. – Юрий Копачевский Apr 03 '18 at 21:08

Expected method to read array element not found on object of type 'id'

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