Question

I have a class that has a NSMutableDictionary as a property:

@interface Alibi : NSObject <NSCopying>
@property (nonatomic, copy) NSMutableDictionary * alibiDetails;
@end

With the following constructor:

- (Alibi *)init
{
    self = [super init];
    _alibiDetails = [NSMutableDictionary dictionary];
    return self;
}

and copy method:

- (Alibi *)copyWithZone:(NSZone *)zone
{
    Alibi *theCopy = [[Alibi alloc] init];
    theCopy.alibiDetails = [self.alibiDetails mutableCopy];    
    return theCopy;
}

When I try to call setObject:ForKey: I get a runtime error mutating method sent to immutable object.

I have the Alibi object declared in the view controller as @property (copy, nonatomic) Alibi * theAlibi; and I initialize it with self.theAlibi = [[Alibi alloc] init]; in viewDidLoad.

The line which crashes is:

NSString * recipient;
recipient = @"Boss";
[self.theAlibi.alibiDetails setObject:recipient forKey:@"Recipient"];

Please let me know what I am doing wrong here. I am coding for iOS 5 on iPhone.

Answer 1

You have a ‘copy’ property, which means exactly that – your NSMutableDictionary will get the -copy method called and return a regular NSDictionary before being assigned to the synthesized instance variable. This thread provides some information on some of your options as to solving this.