CODEWITHSUNDEEP
iosobjective-c
DarthGalm
DarthGalm

Reputation: 45

"variable is not assignable (missing __block type specifier)" error when using a variable from method declaration in method block

I'm developing a small iOs application which retrieves information from a server, and I found the pretty useful NSURLSessionDataTask. First I used a @property (nonatomic, strong) NSMutableArray *objectArray; which I called in my method: 

    - (void) createObjectsArrayFromUrl: (NSString *) url {
NSURL *URL = [NSURL URLWithString:url];
NSURLRequest *request = [NSURLRequest requestWithURL:URL];
NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *task = [session dataTaskWithRequest:request
                                        completionHandler:
                              ^(NSData *data, NSURLResponse *response, NSError *error) {
                                  if(error) {
                                      //error handling
                                  }
                                  dispatch_async(dispatch_get_main_queue(), ^{

                                     NSMutableDictionary *jsonDataDictionary = [objectModel getJsonData];

                    self.objectArray = [objectModel arrayFromDictionary:jsonDataDictionary];

                                      [[self collectionView] reloadData];

                                  });
                              }];
[task resume];
}

And it all went smooth. Now I want to create a universal method, for more arrays, and I thought to do it by passing the array to the method, and updating it inside, like this:

- (void) createObjectsArrayFromUrl: (NSString *) url inArray: (NSMutableArray *) objectArray{
    NSURL *URL = [NSURL URLWithString:url];
    NSURLRequest *request = [NSURLRequest requestWithURL:URL];
    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request
                                            completionHandler:
                                  ^(NSData *data, NSURLResponse *response, NSError *error) {
                                      if(error) {
                                          //error handling
                                      }
                                      dispatch_async(dispatch_get_main_queue(), ^{

                                         NSMutableDictionary *jsonDataDictionary = [objectModel getJsonData];

                        objectArray = [objectModel arrayFromDictionary:jsonDataDictionary];

                                          [[self collectionView] reloadData];

                                      });
                                  }];
    [task resume];
    }

but it gives me the error in the title in the following line: objectArray = [objectModel arrayFromDictionary:jsonDataDictionary]; and I don't know how to proceed. So my idea is, instead of creating a method for every array I have, like before, I want to pass the array as a variable and update it in the method. How to achieve this? Thanks.

Upvotes: 3

Views: 8104

Answers (2)

Sean Lintern
Sean Lintern

Reputation: 3141

Instead of 

objectArray = [objectModel arrayFromDictionary:jsonDataDictionary];

try 

[objecyArray removeAllObjects];
[objectArray addObjectsFromArray:[objectModel arrayFromDictionary:jsonDataDictionary]];

This is because the variable coming in does not have __block in front of it thus allowing it to be used in a block, this is only available for local variables and not parameters. I believe __block does so under the hood stuff to allowing to be referenced inside a block.

Upvotes: 1

Ketan Parmar
Ketan Parmar

Reputation: 27448

If you want to access variable in block then you should assign it as block first like __block NSArray *arr;. then you can access that variable in block means in your completion handler.

In your code you can add one line at start of the method body like,

__block NSArray *arr =  objectArray;

And then use this arr in block like,

 arr = [objectModel arrayFromDictionary:jsonDataDictionary];

Hope this will help :)

Upvotes: 17

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