How to Pass Data Backwards to a View Controller After Passing Forward

Pass data back to previous viewcontroller

You can use a delegate. So in your ViewController B you need to create a protocol that sends data back to your ViewController A. Your ViewController A would become a delegate of ViewController B.

If you are new to objective C, please look at What is Delegate.

Create protocol in ViewControllerB.h :

#import <UIKit/UIKit.h>

@protocol senddataProtocol <NSObject>

-(void)sendDataToA:(NSArray *)array; //I am thinking my data is NSArray, you can use another object for store your information. 

@end

@interface ViewControllerB : UIViewController

@property(nonatomic,assign)id delegate;

ViewControllerB.m

@synthesize delegate;
-(void)viewWillDisappear:(BOOL)animated
{
     [delegate sendDataToA:yourdata];

}

in your ViewControllerA : when you go to ViewControllerB

ViewControllerA *acontollerobject=[[ViewControllerA alloc] initWithNibName:@"ViewControllerA" bundle:nil];
acontollerobject.delegate=self; // protocol listener
[self.navigationController pushViewController:acontollerobject animated:YES];

and define your function:

-(void)sendDataToA:(NSArray *)array
{
   // data will come here inside of ViewControllerA
}

Edited :

You can See this example : How you can Pass data back to previous viewcontroller: Tutorial link

Swift passing calculated data back to previous view controller

My suggestion is to use a callback closure. It's less code and easier to handle than protocol / delegate.

In AddSubtractMoney declare a callback variable and call it in sendBackUpdatedNumber passing the Double value

class AddSubtractMoney: UIViewController {

   // ...

    var callback : ((Double)->())?

  // ...

    func sendBackUpdatedNumber(){

        let newestUpdate = UserInfo(whatYouSpentToday: runningNumber, oldDailyBudgetPassed: dailyBudgetPassedThrough)
        amountPassedBackToUserInfo = dailyBudgetPassedThrough - Double(runningNumber)!
        newestUpdate.goalToSaveDaily = amountPassedBackToUserInfo
        print(amountPassedBackToUserInfo)
        callback?(amountPassedBackToUserInfo)
    }
}

In prepare(for segue assign the closure to the callback variable and add the code to be executed on return

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    if segue.identifier == "addOrSubtractMoney"{
        let addOrSubtractMoneyVC = segue.destination as! AddSubtractMoney
        addOrSubtractMoneyVC.callback = { result in
             print(result)
            // do something with the result
        }
        addOrSubtractMoneyVC.dailyBudgetPassedThrough = userDailyBudgetPassedOver
    }
}

Transferring data back to the root ViewController

If you are using segues, you could create an unwind segue and use it instead of popToRootViewController. Here you can see how to create an unwind segue.

Otherwise, based on your hierarchy, before popToRootViewController, you could access your view controller like this:

if let rootVC = navigationController?.viewControllers.first as? YourViewControllerClass {
    rootVC.someProperty = dataToPass
}
navigationController?.popToRootViewController(animated: true)

Passing data from Side Menu back to its original View Controller

Instead of creating a new instance of CountryDetailsVC in tableView(:didSelectRowAt:), you should store a reference to CountryDetailsVC in your parent view controller in a variable, for example in prepare(for:sender:) of the embed segue and then call your function on that variable later on.

Swift 3 - Passing data between a View Controller and after that to another 2

Before calling presentViewController add :

nextViewController.name = yourTextField.text

You could also delete the segue call. That is redundant.

Here is an example that I've used in the past :

    @IBAction func doSegue(_ sender: UIButton) {
        buttonTag = sender.tag

        let storyboard = UIStoryboard (name: "Main", bundle: nil)
        let resultVC = storyboard.instantiateViewController(withIdentifier: "ResultViewController")as! ResultViewController

        // Communicate with new VC - These values are stored in the destination
        // you can set any value stored in the destination VC here
        resultVC.firstValue = buttonTag
        resultVC.secondValue = randomOpponentValue()
        self.navigationController?.pushViewController(resultVC, animated: true)
    }

Swift, Pass data back from popover to view controller

You can use delegate(protocol) methods to send back data to previous view controller.

IN CURRENT VC:

protocol MyProtocol: class
{
    func sendArrayToPreviousVC(myArray:[AnyObject])
}

Make a var in your class.

weak var mDelegate:MyProtocol?

Now call the protocol method when you pop the view controller, with your "properties" array as parameter.

mDelegate?.sendArrayToPreviousVC(properties)

IN PREVIOUS VC:

In your previous VC, set the mDelegate property to self, when you push the current VC.

currentVC.mDelegate = self
//PUSH VC

Now implement the protocol method in your previous VC.

func sendArrayToPreviousVC(myArray:[AnyObject]) {
    //DO YOUR THING
}