Using AFNetworking to query an API endpoint in the AppDelegate before any view controllers appear

AppDelegate.h

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

ViewController.m

#import "AppDelegate.h"
#import "ViewController1.h"
#import "ViewController2.h"
#import "AFHTTPClient.h"
#import "AFHTTPRequestOperation.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    ViewController1 *vc1 = [[ViewController1 alloc] init];
    ViewController2 *vc2 = [[ViewController2 alloc] init];
    
    NSURL *baseURL = [NSURL URLWithString:@"http://jonfriskics.com/"];
    
    // alloc init the AFHTTPClient for your baseURL
    AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:baseURL];
    
    // setup the request to use the GET method for a specific API endpoint (I just made this one up) and don't send any parameters
    NSURLRequest *request = [httpClient requestWithMethod:@"GET"
                                                     path:@"http://jonfriskics.com/webserviceVersionApiEndpoint"
                                               parameters:nil];
    
    // setup the AFHTTPRequestOperation
    AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
    
    // need to let the httpClient know that we're performing an AFHTTPRequestOperation
    [httpClient registerHTTPOperationClass:[AFHTTPRequestOperation class]];
    
    // perform the operation
    [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
                
        // store the response string in an NSString variable so you can use a conditional to check the value
        NSString *versionNumber = [NSString stringWithUTF8String:[responseObject bytes]];
        if([versionNumber isEqualToString:@"1.3b"]) {
            self.window.rootViewController = vc1;
        } else {
            self.window.rootViewController = vc2;
        }
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"error: %@",error.localizedDescription);
    }];
    [operation start];
    
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}