CODEWITHSUNDEEP
iosobjective-c
rihekopo
rihekopo

Reputation: 3350

Returning a value from a block in class method

I would like to create a simple method in one of my helper class that returns an NSString, but I can't figure out the right way to return the value. I get this error inside the if statement.

Variable is not assignable (missing __block type specifier)

+ (NSString *) photoCount {

    NSString *numberOfPhoto = [[NSString alloc] init];

    PFQuery *photoQuery = [PFQuery queryWithClassName:@"PhotoContent"];
    [photoQuery whereKey:@"usr" equalTo:[PFUser currentUser]];
    [photoQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {

        if (objects) {

            numberOfPhoto = [NSString stringWithFormat:@"%d", [objects count]];

        }
    }];

    return numberOfPhoto;

}

What did I wrong? I've tried to return the string directly from the block, but it doesn't helped.

Upvotes: 0

Views: 75

Answers (1)

Rob
Rob

Reputation: 438307

You are calling asynchronous method, so you cannot return the value immediately, but rather you want to adopt the asynchronous completion block pattern:

+ (void) photoCountWithCompletionHandler:(void (^)(NSInteger count, NSError *error))completionHandler {
    NSParameterAssert(completionHandler);

    PFQuery *photoQuery = [PFQuery queryWithClassName:@"PhotoContent"];
    [photoQuery whereKey:@"usr" equalTo:[PFUser currentUser]];
    [photoQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (objects) {
            completionHandler([objects count], nil);
        } else {
            completionHandler(-1, error);
        }
    }];
}

And then when you call it, it would be something like:

[MyClass photoCountWithCompletionHandler:^(NSInteger count, NSError *error) {
    if (error) {
        // handle the error here
        NSLog(@"photoCountWithCompletionHandler error: %@", error);
        self.textLabel.text = @"?";
    } else {
        // use `count` here
        self.textLabel.text = [NSString stringWithFormat:@"%ld", (long) count];
    }
}];

// do not use `count` here, as the above block is called later, asynchronously

Upvotes: 2

Related Questions