Replacing the button to a custom one as suggested on another answer is possibly not a great idea as you will lose the default behavior and style.

One other option you have is to implement the viewWillDisappear method on the View Controller and check for a property named isMovingFromParentViewController. If that property is true, it means the View Controller is disappearing because it's being removed (popped).

Should look something like:

override func viewWillDisappear(_ animated: Bool) {

    super.viewWillDisappear(animated)



    if self.isMovingFromParentViewController {

        // Your code...

    }

}

In swift 4.2

override func viewWillDisappear(_ animated: Bool) {

    super.viewWillDisappear(animated)



    if self.isMovingFromParent {

        // Your code...

    }

}

override func willMove(toParentViewController parent: UIViewController?)

{

    super.willMove(toParentViewController: parent)

    if parent == nil

    {

        print("This VC is 'will' be popped. i.e. the back button was pressed.")

    }

}

I created this (swift) class to create a back button exactly like the regular one, including back arrow. It can create a button with regular text or with an image.

Usage

weak var weakSelf = self



// Assign back button with back arrow and text (exactly like default back button)

navigationItem.leftBarButtonItems = CustomBackButton.createWithText("YourBackButtonTitle", color: UIColor.yourColor(), target: weakSelf, action: #selector(YourViewController.tappedBackButton))



// Assign back button with back arrow and image

navigationItem.leftBarButtonItems = CustomBackButton.createWithImage(UIImage(named: "yourImageName")!, color: UIColor.yourColor(), target: weakSelf, action: #selector(YourViewController.tappedBackButton))



func tappedBackButton() {



    // Do your thing



    self.navigationController!.popViewControllerAnimated(true)

}

CustomBackButtonClass

(code for drawing the back arrow created with Sketch & Paintcode plugin)

class CustomBackButton: NSObject {



    class func createWithText(text: String, color: UIColor, target: AnyObject?, action: Selector) -> [UIBarButtonItem] {

        let negativeSpacer = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.FixedSpace, target: nil, action: nil)

        negativeSpacer.width = -8

        let backArrowImage = imageOfBackArrow(color: color)

        let backArrowButton = UIBarButtonItem(image: backArrowImage, style: UIBarButtonItemStyle.Plain, target: target, action: action)

        let backTextButton = UIBarButtonItem(title: text, style: UIBarButtonItemStyle.Plain , target: target, action: action)

        backTextButton.setTitlePositionAdjustment(UIOffset(horizontal: -12.0, vertical: 0.0), forBarMetrics: UIBarMetrics.Default)

        return [negativeSpacer, backArrowButton, backTextButton]

    }



    class func createWithImage(image: UIImage, color: UIColor, target: AnyObject?, action: Selector) -> [UIBarButtonItem] {

        // recommended maximum image height 22 points (i.e. 22 @1x, 44 @2x, 66 @3x)

        let negativeSpacer = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.FixedSpace, target: nil, action: nil)

        negativeSpacer.width = -8

        let backArrowImageView = UIImageView(image: imageOfBackArrow(color: color))

        let backImageView = UIImageView(image: image)

        let customBarButton = UIButton(frame: CGRectMake(0,0,22 + backImageView.frame.width,22))

        backImageView.frame = CGRectMake(22, 0, backImageView.frame.width, backImageView.frame.height)

        customBarButton.addSubview(backArrowImageView)

        customBarButton.addSubview(backImageView)

        customBarButton.addTarget(target, action: action, forControlEvents: .TouchUpInside)

        return [negativeSpacer, UIBarButtonItem(customView: customBarButton)]

    }



    private class func drawBackArrow(frame frame: CGRect = CGRect(x: 0, y: 0, width: 14, height: 22), color: UIColor = UIColor(hue: 0.59, saturation: 0.674, brightness: 0.886, alpha: 1), resizing: ResizingBehavior = .AspectFit) {

        /// General Declarations

        let context = UIGraphicsGetCurrentContext()!



        /// Resize To Frame

        CGContextSaveGState(context)

        let resizedFrame = resizing.apply(rect: CGRect(x: 0, y: 0, width: 14, height: 22), target: frame)

        CGContextTranslateCTM(context, resizedFrame.minX, resizedFrame.minY)

        let resizedScale = CGSize(width: resizedFrame.width / 14, height: resizedFrame.height / 22)

        CGContextScaleCTM(context, resizedScale.width, resizedScale.height)



        /// Line

        let line = UIBezierPath()

        line.moveToPoint(CGPoint(x: 9, y: 9))

        line.addLineToPoint(CGPoint.zero)

        CGContextSaveGState(context)

        CGContextTranslateCTM(context, 3, 11)

        line.lineCapStyle = .Square

        line.lineWidth = 3

        color.setStroke()

        line.stroke()

        CGContextRestoreGState(context)



        /// Line Copy

        let lineCopy = UIBezierPath()

        lineCopy.moveToPoint(CGPoint(x: 9, y: 0))

        lineCopy.addLineToPoint(CGPoint(x: 0, y: 9))

        CGContextSaveGState(context)

        CGContextTranslateCTM(context, 3, 2)

        lineCopy.lineCapStyle = .Square

        lineCopy.lineWidth = 3

        color.setStroke()

        lineCopy.stroke()

        CGContextRestoreGState(context)



        CGContextRestoreGState(context)

    }



    private class func imageOfBackArrow(size size: CGSize = CGSize(width: 14, height: 22), color: UIColor = UIColor(hue: 0.59, saturation: 0.674, brightness: 0.886, alpha: 1), resizing: ResizingBehavior = .AspectFit) -> UIImage {

        var image: UIImage



        UIGraphicsBeginImageContextWithOptions(size, false, 0)

        drawBackArrow(frame: CGRect(origin: CGPoint.zero, size: size), color: color, resizing: resizing)

        image = UIGraphicsGetImageFromCurrentImageContext()

        UIGraphicsEndImageContext()



        return image

    }



    private enum ResizingBehavior {

        case AspectFit /// The content is proportionally resized to fit into the target rectangle.

        case AspectFill /// The content is proportionally resized to completely fill the target rectangle.

        case Stretch /// The content is stretched to match the entire target rectangle.

        case Center /// The content is centered in the target rectangle, but it is NOT resized.



        func apply(rect rect: CGRect, target: CGRect) -> CGRect {

            if rect == target || target == CGRect.zero {

                return rect

            }



            var scales = CGSize.zero

            scales.width = abs(target.width / rect.width)

            scales.height = abs(target.height / rect.height)



            switch self {

                case .AspectFit:

                    scales.width = min(scales.width, scales.height)

                    scales.height = scales.width

                case .AspectFill:

                    scales.width = max(scales.width, scales.height)

                    scales.height = scales.width

                case .Stretch:

                    break

                case .Center:

                    scales.width = 1

                    scales.height = 1

            }



            var result = rect.standardized

            result.size.width *= scales.width

            result.size.height *= scales.height

            result.origin.x = target.minX + (target.width - result.width) / 2

            result.origin.y = target.minY + (target.height - result.height) / 2

            return result

        }

    }

}

SWIFT 3.0

class CustomBackButton: NSObject {



    class func createWithText(text: String, color: UIColor, target: AnyObject?, action: Selector) -> [UIBarButtonItem] {

        let negativeSpacer = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.fixedSpace, target: nil, action: nil)

        negativeSpacer.width = -8

        let backArrowImage = imageOfBackArrow(color: color)

        let backArrowButton = UIBarButtonItem(image: backArrowImage, style: UIBarButtonItemStyle.plain, target: target, action: action)

        let backTextButton = UIBarButtonItem(title: text, style: UIBarButtonItemStyle.plain , target: target, action: action)

        backTextButton.setTitlePositionAdjustment(UIOffset(horizontal: -12.0, vertical: 0.0), for: UIBarMetrics.default)

        return [negativeSpacer, backArrowButton, backTextButton]

    }



    class func createWithImage(image: UIImage, color: UIColor, target: AnyObject?, action: Selector) -> [UIBarButtonItem] {

        // recommended maximum image height 22 points (i.e. 22 @1x, 44 @2x, 66 @3x)

        let negativeSpacer = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.fixedSpace, target: nil, action: nil)

        negativeSpacer.width = -8

        let backArrowImageView = UIImageView(image: imageOfBackArrow(color: color))

        let backImageView = UIImageView(image: image)

        let customBarButton = UIButton(frame: CGRect(x: 0, y: 0, width: 22 + backImageView.frame.width, height: 22))

        backImageView.frame = CGRect(x: 22, y: 0, width: backImageView.frame.width, height: backImageView.frame.height)

        customBarButton.addSubview(backArrowImageView)

        customBarButton.addSubview(backImageView)

        customBarButton.addTarget(target, action: action, for: .touchUpInside)

        return [negativeSpacer, UIBarButtonItem(customView: customBarButton)]

    }



    private class func drawBackArrow(_ frame: CGRect = CGRect(x: 0, y: 0, width: 14, height: 22), color: UIColor = UIColor(hue: 0.59, saturation: 0.674, brightness: 0.886, alpha: 1), resizing: ResizingBehavior = .AspectFit) {

        /// General Declarations

        let context = UIGraphicsGetCurrentContext()!



        /// Resize To Frame

        context.saveGState()

        let resizedFrame = resizing.apply(CGRect(x: 0, y: 0, width: 14, height: 22), target: frame)

        context.translateBy(x: resizedFrame.minX, y: resizedFrame.minY)

        let resizedScale = CGSize(width: resizedFrame.width / 14, height: resizedFrame.height / 22)

        context.scaleBy(x: resizedScale.width, y: resizedScale.height)



        /// Line

        let line = UIBezierPath()

        line.move(to: CGPoint(x: 9, y: 9))

        line.addLine(to: CGPoint.zero)

        context.saveGState()

        context.translateBy(x: 3, y: 11)

        line.lineCapStyle = .square

        line.lineWidth = 3

        color.setStroke()

        line.stroke()

        context.restoreGState()



        /// Line Copy

        let lineCopy = UIBezierPath()

        lineCopy.move(to: CGPoint(x: 9, y: 0))

        lineCopy.addLine(to: CGPoint(x: 0, y: 9))

        context.saveGState()

        context.translateBy(x: 3, y: 2)

        lineCopy.lineCapStyle = .square

        lineCopy.lineWidth = 3

        color.setStroke()

        lineCopy.stroke()

        context.restoreGState()



        context.restoreGState()

    }



    private class func imageOfBackArrow(_ size: CGSize = CGSize(width: 14, height: 22), color: UIColor = UIColor(hue: 0.59, saturation: 0.674, brightness: 0.886, alpha: 1), resizing: ResizingBehavior = .AspectFit) -> UIImage {

        var image: UIImage



        UIGraphicsBeginImageContextWithOptions(size, false, 0)

        drawBackArrow(CGRect(origin: CGPoint.zero, size: size), color: color, resizing: resizing)

        image = UIGraphicsGetImageFromCurrentImageContext()!

        UIGraphicsEndImageContext()



        return image

    }



    private enum ResizingBehavior {

        case AspectFit /// The content is proportionally resized to fit into the target rectangle.

        case AspectFill /// The content is proportionally resized to completely fill the target rectangle.

        case Stretch /// The content is stretched to match the entire target rectangle.

        case Center /// The content is centered in the target rectangle, but it is NOT resized.



        func apply(_ rect: CGRect, target: CGRect) -> CGRect {

            if rect == target || target == CGRect.zero {

                return rect

            }



            var scales = CGSize.zero

            scales.width = abs(target.width / rect.width)

            scales.height = abs(target.height / rect.height)



            switch self {

            case .AspectFit:

                scales.width = min(scales.width, scales.height)

                scales.height = scales.width

            case .AspectFill:

                scales.width = max(scales.width, scales.height)

                scales.height = scales.width

            case .Stretch:

                break

            case .Center:

                scales.width = 1

                scales.height = 1

            }



            var result = rect.standardized

            result.size.width *= scales.width

            result.size.height *= scales.height

            result.origin.x = target.minX + (target.width - result.width) / 2

            result.origin.y = target.minY + (target.height - result.height) / 2

            return result

        }

    }

}

I was able to achieve this with the following :

Swift 3

override func didMoveToParentViewController(parent: UIViewController?) {

   super.didMoveToParentViewController(parent)



   if parent == nil {

      println("Back Button pressed.")

      delegate?.goingBack()

   }           

}

Swift 4

override func didMove(toParent parent: UIViewController?) {

    super.didMove(toParent: parent)



    if parent == nil {

        debugPrint("Back Button pressed.")

    }

}

No need of custom back button.

If you want to have back button with back arrow you can use an image and code below

backArrow.png backArrow@2x.png backArrow@3x.png

override func viewDidLoad() {

    super.viewDidLoad()

    let customBackButton = UIBarButtonItem(image: UIImage(named: "backArrow") , style: .plain, target: self, action: #selector(backAction(sender:)))

    customBackButton.imageInsets = UIEdgeInsets(top: 2, left: -8, bottom: 0, right: 0)

    navigationItem.leftBarButtonItem = customBackButton

}



func backAction(sender: UIBarButtonItem) {

    // custom actions here

    navigationController?.popViewController(animated: true)

}

If you are using navigationController then add the UINavigationControllerDelegate protocol to class and add the delegate method as follows:

class ViewController:UINavigationControllerDelegate {



    func navigationController(navigationController: UINavigationController, willShowViewController viewController: UIViewController,

animated: Bool) {

        if viewController === self {

            // do here what you want

        }

    }

}

This method is called whenever the navigation controller will slide to a new screen. If the back button was pressed, the new view controller is ViewController itself.

NO

override func willMove(toParentViewController parent: UIViewController?) { }

This will get called even if you are segueing to the view controller in which you are overriding this method. In which check if the "parent" is nil of not is not a precise way to be sure of moving back to the correct UIViewController. To determine exactly if the UINavigationController is properly navigating back to the UIViewController that presented this current one, you will need to conform to the UINavigationControllerDelegate protocol.

YES

note: MyViewController is just the name of whatever UIViewController you want to detect going back from.

1) At the top of your file add UINavigationControllerDelegate.

class MyViewController: UIViewController, UINavigationControllerDelegate {

2) Add a property to your class that will keep track of the UIViewController that you are segueing from.

class MyViewController: UIViewController, UINavigationControllerDelegate {



var previousViewController:UIViewController

3) in MyViewController's viewDidLoad method assign self as the delegate for your UINavigationController.

override func viewDidLoad() {

    super.viewDidLoad()

    self.navigationController?.delegate = self

}

3) Before you segue, assign the previous UIViewController as this property.

// In previous UIViewController

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

    if segue.identifier == "YourSegueID" {

        if let nextViewController = segue.destination as? MyViewController {

            nextViewController.previousViewController = self

        }

    }

}

4) And conform to one method in MyViewController of the UINavigationControllerDelegate

func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {

    if viewController == self.previousViewController {

        // You are going back

    }

}

In my case the viewWillDisappear worked best. But in some cases one has to modify the previous view controller. So here is my solution with access to the previous view controller and it works in Swift 4:

override func viewWillDisappear(_ animated: Bool) {

        super.viewWillDisappear(animated)

        if isMovingFromParentViewController {

            if let viewControllers = self.navigationController?.viewControllers {

                if (viewControllers.count >= 1) {

                    let previousViewController = viewControllers[viewControllers.count-1] as! NameOfDestinationViewController

                    // whatever you want to do

                    previousViewController.callOrModifySomething()

                }

            }

        }

    }

It's not difficult as we thing. Just create a frame for UIButton with clear background color, assign action for the button and place over the navigationbar back button. And finally remove the button after use.

Here is the Swift 3
sample code done with UIImage instead of UIButton

override func viewDidLoad() {

    super.viewDidLoad()

    let imageView = UIImageView()

    imageView.backgroundColor = UIColor.clear

    imageView.frame = CGRect(x:0,y:0,width:2*(self.navigationController?.navigationBar.bounds.height)!,height:(self.navigationController?.navigationBar.bounds.height)!)

    let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(back(sender:)))

    imageView.isUserInteractionEnabled = true

    imageView.addGestureRecognizer(tapGestureRecognizer)

    imageView.tag = 1

    self.navigationController?.navigationBar.addSubview(imageView)

    }

write the code need to be executed

func back(sender: UIBarButtonItem) {



    // Perform your custom actions}

    _ = self.navigationController?.popViewController(animated: true)



    }

Remove the subView after action is performed

override func viewWillDisappear(_ animated: Bool) {

    super.viewWillDisappear(animated)



    for view in (self.navigationController?.navigationBar.subviews)!{

        if view.tag == 1 {

            view.removeFromSuperview()

        }

    }

Swift 3:

override func didMove(toParentViewController parent: UIViewController?) {

    super.didMove(toParentViewController: parent)



    if parent == nil{

        print("Back button was clicked")

    }

}

Try this .

self.navigationItem.leftBarButtonItem?.target = "methodname"

func methodname ( ) {            

  //    enter code here

}

Try on this too.

override func viewWillAppear(animated: Bool) {

  //empty your array

}

As I understand you want to empty your array as you press your back button and pop to your previous ViewController let your Array which you loaded on this screen is

let settingArray  = NSMutableArray()

@IBAction func Back(sender: AnyObject) {

    self. settingArray.removeAllObjects()

    self.dismissViewControllerAnimated(true, completion: nil)

} 

    override public func viewDidLoad() {

         super.viewDidLoad()

         self.navigationController?.navigationBar.topItem?.title = GlobalVariables.selectedMainIconName

         let image = UIImage(named: "back-btn")



         image = image?.imageWithRenderingMode(UIImageRenderingMode.AlwaysOriginal)



        self.navigationItem.leftBarButtonItem = UIBarButtonItem(image: image, style: UIBarButtonItemStyle.Plain, target: self, action: #selector(Current[enter image description here][1]ViewController.back) )

    }



    func back() {

      self.navigationController?.popToViewController( self.navigationController!.viewControllers[ self.navigationController!.viewControllers.count - 2 ], animated: true)

    }

I accomplished this by calling/overriding viewWillDisappear and then accessing the stack of the navigationController like this:

override func viewWillDisappear(animated: Bool) {

    super.viewWillDisappear(animated)



    let stack = self.navigationController?.viewControllers.count



    if stack >= 2 {

        // for whatever reason, the last item on the stack is the TaskBuilderViewController (not self), so we only use -1 to access it

        if let lastitem = self.navigationController?.viewControllers[stack! - 1] as? theViewControllerYoureTryingToAccess {

            // hand over the data via public property or call a public method of theViewControllerYoureTryingToAccess, like

            lastitem.emptyArray()

            lastitem.value = 5

        }

    }

}

just do control + drag the bar item to below func. work like charm

@IBAction func done(sender: AnyObject) {

    if((self.presentingViewController) != nil){

        self.dismiss(animated: false, completion: nil)

        print("done")

    }

}

Swift 4.2:

override func viewWillDisappear(_ animated: Bool) {

    super.viewWillDisappear(animated)



    if self.isMovingFromParent {

        // Your code...



    }

}

This is how I solved it for my own problem

override func viewWillAppear(_ animated: Bool) {

    super.viewWillAppear(animated)

    self.navigationItem.leftBarButtonItem?.action = #selector(self.back(sender:))

    self.navigationItem.leftBarButtonItem?.target = self

}



@objc func back(sender: UIBarButtonItem) {



}