Objective-C: What does this code mean?

Question

In the MyViewController.h file:

@property (nonatomic, copy, nullable, class) void (^saveMetadataSuccess)(MyViewController*const _Nullable myViewController);

In the MyViewController.m file:

void (^saveMetadataSuccess)(MyViewControllerr* const myViewController) = nil;

+ (void)setSaveMetadataSuccess:(void (^)(MyViewController* const))newMetadataSaveSuccess {
    saveMetadataSuccess = [newMetadataSaveSuccess copy];
}

+ (void (^)(MyViewController* const))saveMetadataSuccess {
    return saveMetadataSuccess;
}

And finally the method which I don't understand:

- (void)success {
dispatch_async(dispatch_get_main_queue(), ^{
        MyViewController.saveMetadataSuccess(self);
    });
}

From my understanding, saveMetadataSuccess is a getter, but MyViewController.saveMetadataSuccess(self);seems to set something.

Can somebody enlighten me?

Thanks

Answer 1

MyViewController.saveMetadataSuccess is a getter and it returns a block that then being called with a param (self).

So it's like a function that returns other function.

Also you must not just call MyViewController.saveMetadataSuccess(self); because MyViewController.saveMetadataSuccess is nullable and it will crash if MyViewController.saveMetadataSuccess is null.

You have to check MyViewController.saveMetadataSuccess first:

- (void)success {
dispatch_async(dispatch_get_main_queue(), ^{
        if (MyViewController.saveMetadataSuccess) {
            MyViewController.saveMetadataSuccess(self);
        }
    });

}