Passing a parameter into a block

Question

I'm trying to pass a parameter into a block but every configuration i do is throwing errors. The parameter im trying to pass in is of type Venue as you can see below.

Here is my perhaps incorrect declaration in the header

-(void)update:(Venue* (^)(NSArray *myScenes, NSError *error))block;

Here is my implementation which i know is wrong because i cant reference the passed in variable but its the only thing not throwing an error

-(void)update:(Venue* (^)(NSArray *myScenes, NSError *error))block{ //download scenes PFQuery *query = [PFQuery queryWithClassName:@"Scenes"]; [query orderByDescending:@"createdAt"]; [query whereKey:@"venueId" equalTo:venue.objectId]; [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { if (error) { NSLog(@"Error: %@ %@", error, [error userInfo]); } else { // We found messages! scenes = objects; //[PFObject pinAllInBackground:objects]; NSLog(@"Retrieved %lu messages", (unsigned long)[scenes count]); NSLog(@"Venues = %@", scenes); } }]; }

and heres how im calling it

[_venues[0] update:^Venue *(NSArray *myScenes, NSError *error) { if (error) { NSLog(@"Error: %@ %@", error, [error userInfo]); } else { NSLog(@"myObjects are: %@", myScenes); _venues[0].scenes = myScenes; } }];

wrong again. Basically i want to know how to declare this in a way that lets me pass in a variable of type Venue*

goshdarnblocksyntax.com

matt
– matt

2015-12-23 03:06:00 +00:00
Commented Dec 23, 2015 at 3:06 — matt
– matt, Commented Dec 23, 2015 at 3:06

siburb · Accepted Answer · 2015-12-23 03:21:31Z

The format is as follows:

- (void)someMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName;

This example is from http://goshdarnblocksyntax.com/

But you're not trying to set the "returnType" of the block, I think that you just want to pass a "Venue*" into the method, and then call the block when your PFQuery finds it's objects?

In which case, you'd need to do something more like this:

- (void)updateVenue:(Venue*)venue completion:(void(^)(NSArray *myScenes, NSError *error))completion{

And then inside the method do the following:

[query findObjectsInBackgroundWithBlock:^(NSArray *scenes, NSError *error) { if (error) { NSLog(@"Error: %@ %@", error, [error userInfo]); } else { // We found messages! //[PFObject pinAllInBackground:scenes]; NSLog(@"Retrieved %lu messages", (unsigned long)[scenes count]); NSLog(@"Venues = %@", scenes); } if (completion) completion(scenes, error); }];

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