Sending “NSString *_strong*to parameter of type _u

问题:

Im getting the following error

Sending "NSString *_strong*to parameter of type _unsafe_unretained id* "changes retain/release properties of pointer ...

in the following line: [theDict getObjects:values andKeys:keys]; Im trying to add an address from contacts to my app. Could someone explain to me what its complaining about? I think its an ARC issue, possibly to do with manual memory management? but im unsure how to fix it.

   - (BOOL)peoplePickerNavigationController:
(ABPeoplePickerNavigationController *)peoplePicker
  shouldContinueAfterSelectingPerson:(ABRecordRef)person
                            property:(ABPropertyID)property
                          identifier:(ABMultiValueIdentifier)identifier


 {
    if (property == kABPersonAddressProperty) {
    ABMultiValueRef multi = ABRecordCopyValue(person, property);

    NSArray *theArray = (__bridge id)ABMultiValueCopyArrayOfAllValues(multi);

    const NSUInteger theIndex = ABMultiValueGetIndexForIdentifier(multi, identifier);

    NSDictionary *theDict = [theArray objectAtIndex:theIndex];

    const NSUInteger theCount = [theDict count];

    NSString *keys[theCount];

    NSString *values[theCount];

    [theDict getObjects:values andKeys:keys]; <<<<<<<<< error here

    NSString *address;
    address = [NSString stringWithFormat:@"%@, %@, %@",
               [theDict objectForKey: (NSString *)kABPersonAddressStreetKey],
               [theDict objectForKey: (NSString *)kABPersonAddressZIPKey],
               [theDict objectForKey: (NSString *)kABPersonAddressCountryKey]];

    _town.text = address;

    [ self dismissModalViewControllerAnimated:YES ];

        return YES;
}
return YES;
 }

回答1:

The docs for NSDictionary getObjects:andKeys: show it as:

- (void)getObjects:(id __unsafe_unretained [])objects andKeys:(id __unsafe_unretained [])keys

But the two values you are passing in are strong NSString references (local variables and ivars are strong by default. This is why there is the ARC error. Your parameters don't match the expected types.

Change:

NSString *keys[theCount];
NSString *values[theCount];

to:

NSString * __unsafe_unretained keys[theCount];
NSString * __unsafe_unretained values[theCount];

should fix the compiler issue.

This change means that none of the objects in your arrays are safely retained. But as long as 'theDict' doesn't go out scope before 'keys' and 'values' then you will be OK.

回答2:

You're correct that it's an ARC error, its confused that you're trying to both assign NSArrays to NSStrings and you've tried to create an array of NSStrings, which I'm not sure will work in the way you intend.

I don't see where you're using them later, however you'll want to do

NSArray *keys, *values;

to get rid of the errors.