Cannot access UITabBarController from modal ViewController - ios

Question

I have a UITabBarController-based application in which my login page is presented modally by the default tab's VC(UITabBarController index 0), and is dismissed modally by dismissViewControllerAnimated:.
From my settings page I have a logout button, and if the user immediately logs back in I have to call [self.presentingViewController.presentingViewController dismissViewControllerAnimated:YES completion:nil]; and then reset the UITabBarController's selectedIndex property in order to get rid of the settings page and also go back to the starting tabBar tab. So I do this:
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSString* responseString = [[NSString alloc] initWithData:_responseData encoding:NSUTF8StringEncoding];
/*Succesful Login*/
if([responseString isEqualToString:#"success"])
{
UITabBarController *tabBarController = (UITabBarController *)self.presentingViewController;
if (tabBarController){
NSLog(#"I have a tab bar~");
[self.tabBarController setSelectedIndex:0];
}
else{
NSLog(#"I don't have a tab bar~");
}
//dismisses from a second, immediate, re-login attempt
[self.presentingViewController.presentingViewController dismissViewControllerAnimated:YES completion:nil];
//dismisses from first login attempt
[self dismissViewControllerAnimated:YES completion:nil];
NSLog(#"Succesful login.");
}
In this case, the method setSeletedIndex: does not work because this methodology essentially creates a new instance of the tabBarController, when it is the original that is actually displayed. I CAN NOT seem to access the already existing UITabBarController which was before my modally presented login page.
EDIT:
I have tried using this conditional to check its existence:
if (self.tabBarController){
NSLog(#"I have a tab bar~");
//[self.tabBarController setSelectedIndex:0];
}
else{
NSLog(#"I don't have a tab bar~");
}
where I have even changed self.tabBarController to self.presentingViewController.tabBarController and get nil, and self.presentingViewController.presentingViewController.tabBarController and get nil, how am I to access the previously existing UITabBarController?
Objective: Access the application's UITabBarController that is present before the presentation of the login page. (Access the Appdelegate's UITabBarController)

Answer 1

Your use case is a natural fit for delegation.
In the header file for your Login, define a delegate. E.g.,
#class Login
#protocol LoginDelegate <NSObject>
#required
- (void) userDoneWithLoginController:(Login *) controller;
#end
#interface Login: UIViewController
#property (weak, nonatomic) id<LoginDelegate> viewDelegate;
#end
Then your presenting view controller segue can set itself as the delegate to the login view controller by setting this "viewDelegate" object inside the prepareForSegue for the presenting view controller before control passes to the Login page. [Let me know if you want this clarified.]
In addition the presenting view controller will implement the required method--which can simply dismiss the login page when called
-(void) userDoneWithLoginController:(Login *) controller
{
[controller dismissViewControllerAnimated:YES completion:nil];
}
Once you've done this, the login page simply calls its delegate method when it is done, thusly:
[self.viewDelegate userDoneWithLoginController:self];
Viola!
This is preferred way to dismiss a modal view in iOS. The calling controller should be the controller dismissing the view. Try to avoid having view controllers dismiss themselves. Instead, have their calling/presenting controllers (delegates) dismiss them.

Answer 2

The following should work.
// check that the vc presenting your current modal vc is a tab bar controller
if ([self.presentingViewController isKindOfClass:[UITabBarController class]]) {
// get the pointer of type UITabBarController
UITabBarController *tabBarController = (UITabBarController *)self.presentingViewController;
// set to the desired tab
tabBarController.selectedIndex = 2;
}
// dismiss the current modal vc
[self.presentingViewController dismissViewControllerAnimated:YES completion:nil];

Answer 3

I believe I found my solution.
I was able to access the app's UITabBarController from the Appdelegate like so:
MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
[[appDelegate myTabBar] setSelectedIndex:0];