iOS - Passing blocks to functions

Question

I have a method call (it's a call from AFNetworking): ``` AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) { NSLog(@"IP Address: %@", [JSON valueForKeyPath:@"origin"]); } failure:^(NSURLRequest *request , NSURLResponse *response , NSError *error , id JSON) { NSLog(@"Failed: %@",[error localizedDescription]); }]; ``` and I'm trying to pull the sucess and failure blocks out into a separate variable, that I can later pass into the method. But I can't figure out how to declare the blocks as variables. I'm looking to do something like this: ``` IDontKnowWhatKindOfDataTypeGoesHere successBlock = ^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) { NSLog(@"IP Address: %@", [JSON valueForKeyPath:@"origin"]); } ``` and the same for the failureBlock. So then I'm looking to make the `AFJSONRequestOperation` call like: ``` AFJSONRequestOperation *operation = [AFJSO…

Accepted Answer

It's awkward until you get used to it. The variable name appears mixed in with the type...

```
void (^success)(NSURLRequest *, NSHTTPURLResponse *, id) = ^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
   NSLog(@"request is %@, response is %@ and json is %@", request, response, JSON);
};
```

The stack variable name in this case is success. You can now refer to it in subsequent expressions that take the same type, like ...

```
AFJSONRequestOperation *operation = [AFJSONRequestOperationJSONRequestOperationWithRequest:request
                                        success:success];
```

You can also make a block an property, like this:

```
@property (copy, nonatomic) void (^success)(NSURLRequest *, NSHTTPURLResponse *, id);
```

And call it like this:

```
self.success(aRequest, aResponse, someJSON);
```

Remember to nil it out when you're done calling it, so the caller has less to worry about creating a retain cycle.

Edit: good suggestion in commentary about using typedef to make this easier on the eyes and fingers:

```
typedef void (^SuccesBlock)(NSURLRequest *, NSHTTPURLResponse *, id);
```

So the stack variable looks like this:

```
SuccessBlock success = ^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
   NSLog(@"request is %@, response is %@ and json is %@", request, response, JSON);
};
```

and the property looks like this:

```
@property (copy, nonatomic) SuccessBlock success;
```

iOS - Passing blocks to functions

Solution

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