How to perform asynchronous request using JSON?

Question

Scenario, I have a data request using JSON but I would like this request to be performed outside the main thread of the app, so that it does not catch and that the user can perform other operations while the data is downloaded.

In the code below I can already download the data normally, but I only need it to be done in a secondary thread.

-(void)recebeTodosOsDadosPorFuncionarioDoWebService{        
    NSMutableString* strURL =[[NSMutableString alloc]initWithFormat:@"http://localhost/advphp/ArquivosFuncionando/pegaDadosNaoLidosPorFuncionario.php?funcionario=%@",funcionarioCadastrado];           
    NSURL* url = [NSURL URLWithString: strURL];        
    NSData* data = [NSData dataWithContentsOfURL:url];        
    NSError*erro;

    arraySalvaDadosProcessos = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&erro];

    if(arraySalvaDados == (id)[NSNull null]|| [arraySalvaDados count] == 0){

       NSLog(@"Erro para receber dados do webservice: \n\n%@", arraySalvaDados);

    }else{

        [self salvaTodosOsDadosRecebidosNoBancoLocal];
    }
}

Answer 1

Sets its class as delegate of <NSURLConnectionDelegate, NSURLConnectionDataDelegate>

Making the requisition:

-(void)performRequest{  
    NSString * urlConnection = [[NSString alloc] initWithFormat:
                                @"Linkaqui"];
    urlConnection = [urlConnection stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    url = [[NSURL alloc] initWithString: urlConnection];
    request = [NSMutableURLRequest requestWithURL: url
                                      cachePolicy: NSURLRequestReloadIgnoringLocalAndRemoteCacheData
                                  timeoutInterval: 4000];
    connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    [connection start];
}

Taking the answer and concatenating into your receivedResponse of the kind NSData declared on its class properties:

-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    [receivedResponse appendData: data];
}

Capturing an error if it occurs:

-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
    NSLog(@"-----> Error %@ <-----", error);
}

When you finish receiving all the data:

-(void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSError       * error     = nil;
    if (receivedResponse != nil && !error) {
        //Chamada assincrona para a manipulação dos dados que obteve com a resposta
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            [self updatingBackground];
        });
    }else{

    }
}

-(void) updatingBackground{
     //Salva todos os dados que receber/mostra, enfim faz todas as operações
}

Answer 2

A simple way to execute background code is by using Grand Central Dispatch (GDC). The dispatch_async method executes a code block asynchronously and returns immediately, that is, it does not block execution in the current stream. You can create your own Dispatch queues or use those defined by default.

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
  //realize aqui o trabalho em background
        dispatch_async(dispatch_get_main_queue(), ^{ 
       //quando as operações em background forem concluídas, execute aqui o código na thread principal para atualização da tela, caso necessário
        });
    });