AFNetworking getting data for XML parse error

This is my AFHTTPClient singleton:

+ (API *)sharedInstance
{
static API *sharedInstance = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    sharedInstance = [[API alloc] initWithBaseURL:[NSURL URLWithString:kAPIHost]];
    [sharedInstance setParameterEncoding:AFJSONParameterEncoding];
    [sharedInstance registerHTTPOperationClass:[AFXMLRequestOperation class]];
    [sharedInstance setDefaultHeader:@"Accept" value:@"application/rss+xml"];
});

return sharedInstance;
}

And method in same class (AFHTTPClient):

- (void)requestXMLDataCompletion:(JSONResponseBlock)completionBlock
{
NSMutableURLRequest *apiRequest = [self requestWithMethod:@"GET" path:kAPIPath parameters:nil];

AFXMLRequestOperation *operation = [[AFXMLRequestOperation alloc] initWithRequest:apiRequest];

[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject){
    // success
    completionBlock(responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    // failure
    completionBlock([NSDictionary dictionaryWithObject:[error localizedDescription] forKey:@"error"]);
}];

[operation start];
}

When I call this function to get XML from RSS I get this error:

error = "Expected content type {(\n    \"application/xml\",\n    \"text/xml\"\n)}, got application/rss+xml";

Question:

1. Is whole concept of implemented singleton good and do I need any changes ?

2. Is there any suggestion if whole concept is wrong ?

3. Why am I getting this error?

Thanks.

• Concept of Singleton

  A singleton is more commonly known as a design pattern. Usually a singleton is a class and behaves exactly like any other class, the only exception being that any instances of a singleton reference the same object data. This means that any instance of a singleton class are actually all the same instance.

You can check out Singleton Pattern for more information and sample code to enforce how the singleton will be used.

• Is there any suggestion if whole concept is wrong ?

  I would suggest you to use Singleton for AFNetworking since you will have only one instance of it.

• Your Error

  The error you are getting is because AFNetworking request wants Header Content-Type as "application/xml" or "text/xml"

Try changing this code:

[self registerHTTPOperationClass:[AFXMLRequestOperation class]]; 

to

[self registerHTTPOperationClass:[AFHTTPRequestOperation class]];