How do I know the app’s web service is down?

Question

Scenario: The app consumes data from a web service, so that the app does not get "locked" I added the task of downloading the data in a secondary trhead, according to the following code:

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
        });
    });

However, when the web service is down, the app is waiting for the server to reply, and after a while without the answer, iOS shuts down my app.

I wonder if there is a Design Pattern for this type of situation, where we can control how long the app will be waiting for server response, and inform iOS to end the data request process without having to close the app!

Answer 1

For web service requests, the most used library is Afnetworking. It makes it easy to handle situations where the request fails, either because of connection or server problems. The library is already in charge of performing background operations, managing multiple requests, among other things.

To use it, add to Podfile pod "AFNetworking". If you don’t already use Cocoapods read the link.

Each request will always have a success block, called if the request successfully completes, and an error block, called when the request fails (for example due to a timeout in the operation). Example:

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:@"http://example.com/resources.json" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSLog(@"JSON: %@", responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"Error: %@", error);
}];