AFNetworking globally prompt user to login on 401 error code? - ios

Question

I have been struggling to find a clean solution for this problem for a few I have created an app which makes multiple restful web service requests which work fine however part of the request the login details or API Key could expire and I need to be able to handle this and present the user the login screen again.
In my API Client class I am doing the following which works fine, however because the app does multiple web service requests I am seeing the UI AlertView multiple times.
Any ideas on how I can make this block of code only run once for the first error which occurs and only show one alert view?
AFJSONRequestOperation *operation = [[AFJSONRequestOperation alloc] initWithRequest:apiRequest];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
completionBlock(responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSInteger statusCode = [operation.response statusCode];
if (statusCode == 401) {
[UIAlertView error:#"Your session has expied, please log in again."];
[[NSNotificationCenter defaultCenter]
postNotificationName:#"Logout"
object:self];
} else {
completionBlock([NSDictionary dictionaryWithObject:[error localizedDescription] forKey:#"error"]);
}
}];

Answer 1

One way would be to create a global variable which contains the current login status. You should check this login status before a request or before the success/failure blocks if the requests are not chained together.
A better approach would be to create a NSOperationQueue to manage the AFJSONRequestOperation objects. This would give you more control over the lifespan of each request. If one returns a 401 then you could cancel all the operations in the queue.
You can find more about creating and using queue here at this link.

Answer 2

Typically you encounter a similar issue when initialising the shared instance of a singleton object that you want to avoid performing the initialisation more than once.
One way to solve this is using Grand Central Dispatch's dispatch_once, as shown below, which is also included in Xcode as a default snippet (GCD: Dispatch Once). In your case you'd present the alert inside the block you pass to dispatch_once.
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
/*code to be executed once*/
});