AFNetworking: is it safe to access variable outside block?

Question

I'm trying to debug an issue when storing variable outside a block.

- (void) setObj : (NSString *) abc {
    [self postURL:@"..." params:@{"abc" : abc} completionHandler:^(id response) {

        [[SharedPref sharedInstance] setX:response];
        [[SharedPref sharedInstance] setAbc:abc]; <-- can we safely do this?

    } failureHandler:^(SBError *error) {

    }];
}

I've seen cases where when in later time I try to access abc, I'm getting empty string.

[[SharedPref sharedInstance] getAbc]; <-- this return empty string

Answer 1

It should be safe as long as the abc property in SharedPref is strong or copy. For NSString* types, it's preferred to use copy.

@interface SharedPref : NSObject
@property (copy,nonatomic) NSString* abc;
@end

The difference is as follows:

strong:

• strong indicates that the class owns the property

• strong increases the reference count of the property by 1

• instance will not be released until its reference count is 0.

copy

• copy assigns a shallow copy when assigning the property by calling [copy]

• copy ensures that you're always dealing with an immutable property. If a mutable property is passed in, it will copy it. If a immutable property is passed in, it will retain it (you would need to dealloc it).