The code below compiles fine, but crashes with an unrecognized selector sent to instance error.
I have one class that inherits from UIViewController:
class Controller: UIViewController {
override func viewDidLoad() {
let toolbarWrapper = CustomToolbarWrapper(view: view, target: self)
let toolbar = toolbarWrapper.toolbarView
view.addSubview(toolbar)
... Other code ...
}
}
And another class that is just a wrapper for a UIView and contains buttons:
class CustomToolbarWrapper {
var toolbarView: UIView
init(view: UIView, target: Any) {
let height: CGFloat = 80
toolbarView = UIView(frame: CGRect(x: 0, y: view.frame.height - height, width: view.frame.width, height: height))
let button = UIButton()
... Some button layout code ...
button.addTarget(target, action: #selector(CustomToolbar.buttonTapped(_:)), for: .touchUpInside)
toolbarView.addSubview(button)
}
#objc static func buttonTapped(_ sender: Any) {
print("button tapped")
}
}
For the sake of clarity, I left out a large chunk of code and kept what I thought was necessary. I think that my code doesn't work because of my misunderstanding of the how the target works in the addTarget function. Normally, I would just use self as the target of my button's action, so I just tried to pass along self from the view controller to the CustomToolbarWrapper's init function.
What else I have tried:
Changing the button's target from target to self like this:
button.addTarget(self, action: #selector(CustomToolbar.buttonTapped(_:)), for: .touchUpInside)
results in the app not crashing anymore. Instead, however, I believe that line of code fails to do anything (which doesn't throw an error for some reason?) because attempting to print button.allTargets or even button.allTargets.count results in the app crashing at compile time, with an EXC_BREAKPOINT error and no error description in the console or the XCode UI (which just confuses me even more because there are no breakpoints in my code!).
Also, making buttonPressed(_:) non-static does not change any of the previously mentioned observations.
Also, to make sure the button could in fact be interacted with, I added this in the viewDidLoad() of Controller:
for subview in toolbar.subviews? {
if let button = subview as? UIButton {
button.addTarget(self, action: #selector(buttonPressed(_:)), for: .touchUpInside)
}
}
and added a simple testing method to Controller for the button:
#objc func buttonPressed(_ sender: UIButton) {
print("Button Pressed")
}
And running the code did result in "Button Pressed" being printed in the console log, so the button should be able to be interacted with by the user.
Feel free to let me know if you think this is not enough code to figure out the problem, and I will post more details.
Edit
I prefer to keep the implementation of the button's action in the CustomToolbarWrapper class to prevent repeating code in the future, since the action will be the same no matter where an instance of CustomToolbarWrapper is created.
The best option would be to add the target in your controller and then call a method in your toolbarWrapper on button press. But if you really need to keep this design, you should have a strong reference to your toolbarWrapper in your controller class, otherwise your toolbarWrapper is deallocated and nothing gets called. Also, the buttonTapped(_:) method does not need to be static. Thus, in your controller:
class Controller: UIViewController {
var toolbarWrapper: CustomToolbarWrapper?
override func viewDidLoad() {
toolbarWrapper = CustomToolbarWrapper(view: view, target: self)
let toolbar = toolbarWrapper.toolbarView
view.addSubview(toolbar)
... Other code ...
}
}
And in your wrapper:
class CustomToolbarWrapper {
var toolbarView: UIView
init(view: UIView, target: Any) {
let height: CGFloat = 80
toolbarView = UIView(frame: CGRect(x: 0, y: view.frame.height - height,width: view.frame.width, height: height))
let button = UIButton()
... Some button layout code ...
button.addTarget(self, action: #selector(buttonTapped(_:)), for: .touchUpInside)
toolbarView.addSubview(button)
}
#objc func buttonTapped(_ sender: Any) {
print("button tapped")
}
}
There is another way I would use which is delegation. The target does not necessarily have to be a controller, it can be the CustomToolbarWrapper itself.
First, declare a protocol
protocol CTDelegate: AnyObject {
func didClickButton()
}
Then in CustomToolbarWrapper add a property, weak var delegate: CTDelegate? and a button action:
#objc func buttonTapped(_ sender: UIButton) {
delegate?.didClickButton()
}
So in your case, it becomes:
button.addTarget(self, action: #selector(CustomToolbarWrapper.buttonTapped(_:)), for: .touchUpInside)
Then when you go to any ViewController, conform to CTDelegate and initialize the CustomToolbarWrapper, you can set its delegate to the controller.
e.g
let toolbarWrapper = CustomToolbarWrapper(view: view, target: self)
toolbarWrapper.delegate = self
and implement your action inside the method you are conforming to in your controller i.e.
func didClickButton()
Your problem is right here:
let toolbarWrapper = CustomToolbarWrapper(view: view, target: self)
You're passing an instance of Controller class which doesn't implement the buttonTapped(_:) selector. It is implemented by your CustomToolbarWrapper class. This is a bad design in general. You should either follow a delegate pattern, or a callback pattern.
Updated Answer:
Delegate pattern solution:
class Controller: UIViewController, CustomToolbarWrapperDelegate {
override func viewDidLoad() {
let toolbarWrapper = CustomToolbarWrapper(view: view, buttonDelegate: self)
let toolbar = toolbarWrapper.toolbarView
view.addSubview(toolbar)
}
// MARK: - CustomToolbarWrapperDelegate
func buttonTapped(inToolbar toolbar: CustomToolbarWrapper) {
print("button tapped")
}
}
protocol CustomToolbarWrapperDelegate: AnyObject {
func buttonTapped(inToolbar toolbar: CustomToolbarWrapper) -> Void
}
class CustomToolbarWrapper {
var toolbarView: UIView
weak var buttonDelegate: CustomToolbarWrapperDelegate?
init(view: UIView, buttonDelegate: CustomToolbarWrapperDelegate?) {
let height: CGFloat = 80
toolbarView = UIView(frame: CGRect(x: 0, y: view.frame.height - height, width: view.frame.width, height: height))
self.buttonDelegate = buttonDelegate
let button = UIButton()
button.addTarget(self, action: #selector(self.buttonTapped(_:)), for: .touchUpInside)
toolbarView.addSubview(button)
}
#objc private func buttonTapped(_ sender: Any) {
// Your button's logic here. Then call the delegate:
self.buttonDelegate?.buttonTapped(inToolbar: self)
}
}
If you'd rather stick to your current design then just implement the following changes:
class Controller: UIViewController {
override func viewDidLoad() {
let toolbarWrapper = CustomToolbarWrapper(view: view, target: self, selector: #selector(self.buttonTapped(_:)), events: .touchUpInside)
let toolbar = toolbarWrapper.toolbarView
view.addSubview(toolbar)
}
#objc private func buttonTapped(_ sender: Any) {
print("button tapped")
}
}
class CustomToolbarWrapper {
var toolbarView: UIView
init(view: UIView, target: Any?, selector: Selector, events: UIControlEvents) {
let height: CGFloat = 80
toolbarView = UIView(frame: CGRect(x: 0, y: view.frame.height - height, width: view.frame.width, height: height))
let button = UIButton()
button.addTarget(target, action: selector, for: events)
toolbarView.addSubview(button)
}
}
I need to execute an action (emptying an array), when the back button of a UINavigationController is pressed, while the button still causes the previous ViewController on the stack to appear. How could I accomplish this using swift?
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...
}
}
One option would be implementing your own custom back button. You would need to add the following code to your viewDidLoad method:
- (void) viewDidLoad {
[super viewDidLoad];
self.navigationItem.hidesBackButton = YES;
UIBarButtonItem *newBackButton = [[UIBarButtonItem alloc] initWithTitle:#"Back" style:UIBarButtonItemStyleBordered target:self action:#selector(back:)];
self.navigationItem.leftBarButtonItem = newBackButton;
}
- (void) back:(UIBarButtonItem *)sender {
// Perform your custom actions
// ...
// Go back to the previous ViewController
[self.navigationController popViewControllerAnimated:YES];
}
UPDATE:
Here is the version for Swift:
override func viewDidLoad {
super.viewDidLoad()
self.navigationItem.hidesBackButton = true
let newBackButton = UIBarButtonItem(title: "Back", style: UIBarButtonItemStyle.Bordered, target: self, action: "back:")
self.navigationItem.leftBarButtonItem = newBackButton
}
#objc func back(sender: UIBarButtonItem) {
// Perform your custom actions
// ...
// Go back to the previous ViewController
self.navigationController?.popViewControllerAnimated(true)
}
UPDATE 2:
Here is the version for Swift 3:
override func viewDidLoad {
super.viewDidLoad()
self.navigationItem.hidesBackButton = true
let newBackButton = UIBarButtonItem(title: "Back", style: UIBarButtonItemStyle.plain, target: self, action: #selector(YourViewController.back(sender:)))
self.navigationItem.leftBarButtonItem = newBackButton
}
#objc func back(sender: UIBarButtonItem) {
// Perform your custom actions
// ...
// Go back to the previous ViewController
_ = navigationController?.popViewController(animated: true)
}
override func willMove(toParent parent: UIViewController?)
{
super.willMove(toParent: parent)
if parent == nil
{
print("This VC is 'will' be popped. i.e. the back button was pressed.")
}
}
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)
}
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
}
}
}
In Swift 5 and Xcode 10.2
Please don't add custom bar button item, use this default behaviour.
No need of viewWillDisappear, no need of custom BarButtonItem etc...
It's better to detect when the VC is removed from it's parent.
Use any one of these two functions
override func willMove(toParent parent: UIViewController?) {
super.willMove(toParent: parent)
if parent == nil {
callStatusDelegate?.backButtonClicked()//Here write your code
}
}
override func didMove(toParent parent: UIViewController?) {
super.didMove(toParent: parent)
if parent == nil {
callStatusDelegate?.backButtonClicked()//Here write your code
}
}
If you want stop default behaviour of back button then add custom BarButtonItem.
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.
You can subclass UINavigationController and override popViewController(animated: Bool). Beside being able to execute some code there you can also prevent the user from going back altogether, for instance to prompt to save or discard his current work.
Sample implementation where you can set a popHandler that gets set/cleared by pushed controllers.
class NavigationController: UINavigationController
{
var popHandler: (() -> Bool)?
override func popViewController(animated: Bool) -> UIViewController?
{
guard self.popHandler?() != false else
{
return nil
}
self.popHandler = nil
return super.popViewController(animated: animated)
}
}
And sample usage from a pushed controller that tracks unsaved work.
let hasUnsavedWork: Bool = // ...
(self.navigationController as! NavigationController).popHandler = hasUnsavedWork ?
{
// Prompt saving work here with an alert
return false // Prevent pop until as user choses to save or discard
} : nil // No unsaved work, we clear popHandler to let it pop normally
As a nice touch, this will also get called by interactivePopGestureRecognizer when the user tries to go back using a swipe gesture.
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()
}
}
}
}
Before leave current controller I need to show alert. So I did it this way:
Add extention to UINavigationController with UINavigationBarDelegate
Add selector to your controller navigationShouldPopOnBack(completion:)
It's worked)
extension UINavigationController: UINavigationBarDelegate {
public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
if let items = navigationBar.items, viewControllers.count < items.count {
return true
}
let clientInfoVC = topViewController as? ClientInfoVC
if clientInfoVC?.responds(to: #selector(clientInfoVC?.navigationShouldPopOnBack)) ?? false {
clientInfoVC?.navigationShouldPopOnBack(completion: { isAllowPop in
if isAllowPop {
DispatchQueue.main.async {
self.popViewController(animated: true)
}
}
})
}
DispatchQueue.main.async {
self.popViewController(animated: true)
}
return false
}
}
#objc func navigationShouldPopOnBack(completion: #escaping (Bool) -> ()) {
let ok = UIAlertAction(title: R.string.alert.actionOk(), style: .default) { _ in
completion(true)
}
let cancel = UIAlertAction(title: R.string.alert.actionCancel(), style: .cancel) { _ in
completion(false)
}
let alertController = UIAlertController(title: "", message: R.string.alert.contractMessage(), preferredStyle: .alert)
alertController.addAction(ok)
alertController.addAction(cancel)
present(alertController, animated: true, completion: nil)
}
When back button is pressed, ignore interactive pop with screen edge gesture.
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if isMovingFromParent, transitionCoordinator?.isInteractive == false {
// code here
}
}
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()
}
}
This is my solution
extension UINavigationController: UINavigationBarDelegate {
public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
if let shouldBlock = self.topViewController?.shouldPopFromNavigation() {
return shouldBlock
}
return true
}
}
extension UIViewController {
#objc func shouldPopFromNavigation() -> Bool {
return true
}
}
In your view controller, you can handle like this:
#objc override func shouldPopFromNavigation() -> Bool {
// Your dialog, example UIAlertViewController or whatever you want
return false
}
Swift 4.2:
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if self.isMovingFromParent {
// Your code...
}
}
For Swift 5, we can check it in view will disappear
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if self.isMovingFromParent {
delegate?.passValue(clickedImage: selectedImage)
}
}
Swift 3:
override func didMove(toParentViewController parent: UIViewController?) {
super.didMove(toParentViewController: parent)
if parent == nil{
print("Back button was clicked")
}
}
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 5 __ Xcode 11.5
In my case I wanted to make an animation, and when it finished, go back.
A way to overwrite the default action of the back button
and call your custom action is this:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
setBtnBack()
}
private func setBtnBack() {
for vw in navigationController?.navigationBar.subviews ?? [] where "\(vw.classForCoder)" == "_UINavigationBarContentView" {
print("\(vw.classForCoder)")
for subVw in vw.subviews where "\(subVw.classForCoder)" == "_UIButtonBarButton" {
let ctrl = subVw as! UIControl
ctrl.removeTarget(ctrl.allTargets.first, action: nil, for: .allEvents)
ctrl.addTarget(self, action: #selector(backBarBtnAction), for: .touchUpInside)
}
}
}
#objc func backBarBtnAction() {
doSomethingBeforeBack { [weak self](isEndedOk) in
if isEndedOk {
self?.navigationController?.popViewController(animated: true)
}
}
}
private func doSomethingBeforeBack(completion: #escaping (_ isEndedOk:Bool)->Void ) {
UIView.animate(withDuration: 0.25, animations: { [weak self] in
self?.vwTxt.alpha = 0
}) { (isEnded) in
completion(isEnded)
}
}
Or you can use this method one time to explore the NavigationBar view hierarchy, and get the indexes to access to the _UIButtonBarButton view, cast to UIControl, remove the target-action, and add your custom targets-actions:
private func debug_printSubviews(arrSubviews:[UIView]?, level:Int) {
for (i,subVw) in (arrSubviews ?? []).enumerated() {
var str = ""
for _ in 0...level {
str += "\t"
}
str += String(format: "%2d %#",i, "\(subVw.classForCoder)")
print(str)
debug_printSubviews(arrSubviews: subVw.subviews, level: level + 1)
}
}
// Set directly the indexs
private func setBtnBack_method2() {
// Remove or comment the print lines
debug_printSubviews(arrSubviews: navigationController?.navigationBar.subviews, level: 0)
let ctrl = navigationController?.navigationBar.subviews[1].subviews[0] as! UIControl
print("ctrl.allTargets: \(ctrl.allTargets)")
ctrl.removeTarget(ctrl.allTargets.first, action: nil, for: .allEvents)
print("ctrl.allTargets: \(ctrl.allTargets)")
ctrl.addTarget(self, action: #selector(backBarBtnAction), for: .touchUpInside)
print("ctrl.allTargets: \(ctrl.allTargets)")
}
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)
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if self.isMovingToParent {
//your code backView
}
}
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)
}
Here is the simplest possible Swift 5 solution that doesn't require you to create a custom back button and give up all that UINavigationController left button functionality you get for free.
As Brandon A recommends above, you need need to implement UINavigationControllerDelegate in the view controller you want to interact with before returning to it. A good way is to create an unwind segue that you can perform manually or automatically and reuse the same code from a custom done button or the back button.
First, make your view controller of interest (the one you want to detect returning to) a delegate of the navigation controller in its viewDidLoad:
override func viewDidLoad() {
super.viewDidLoad()
navigationController?.delegate = self
}
Second, add an extension at the bottom of the file that overrides navigationController(willShow:animated:)
extension PickerTableViewController: UINavigationControllerDelegate {
func navigationController(_ navigationController: UINavigationController,
willShow viewController: UIViewController,
animated: Bool) {
if let _ = viewController as? EditComicBookViewController {
let selectedItemRow = itemList.firstIndex(of: selectedItemName)
selectedItemIndex = IndexPath(row: selectedItemRow!, section: 0)
if let selectedCell = tableView.cellForRow(at: selectedItemIndex) {
performSegue(withIdentifier: "PickedItem", sender: selectedCell)
}
}
}
}
Since your question included a UITableViewController, I included a way to get the index path of the row the user tapped.
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
}
}
}
You can do something in your Viewcontroller like
override func navigationShouldPopOnBackButton() -> Bool {
self.backAction() //Your action you want to perform.
return true
}
For complete answer use
Detecting when the 'back' button is pressed on a navbar
My preference was to override the popViewController in the Navigation Controller. The advantages of this is:
Your app keeps the default Back Button look and animations, and you don't have to manage it. This is particularly helpful if a user has Large Text set on their phone, since the default back button will increase or decrease in size based on the user settings.
You can stop the view from popping altogether, unlike using viewWillDisappear.
First, create a custom Navigation Controller class (and be sure to assign it to the Navigation Controller in your Story Board or wherever your navigation controller is created):
class NavControllerWithBackButtonOverride: UINavigationController {
var backButtonOverride: (() -> Void)? = nil
override func popViewController(animated: Bool) -> UIViewController? {
if backButtonOverride != nil {
//if anything is assigned to the backButtonOverride the override will run
self.backButtonOverride!()
return nil
} else {
//otherwise the default popViewController will run
return super.popViewController(animated: animated)
}
}
}
Then enable/disable the override in your View Controller by assigning a value to the backButtonOverride variable:
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.enableCustomBackButton()
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
self.disableCustomBackButton()
}
/**
Custom Back Button
*/
func customBackButtonAction() {
print("DO THIS INSTEAD")
}
func enableCustomBackButton() {
if let nav = self.navigationController as? NavControllerWithBackButtonOverride {
nav.backButtonOverride = { self.customBackButtonAction() }
nav.interactivePopGestureRecognizer?.isEnabled = false
}
}
func disableCustomBackButton() {
if let nav = self.navigationController as? NavControllerWithBackButtonOverride {
nav.backButtonOverride = nil
nav.interactivePopGestureRecognizer?.isEnabled = true
}
}
Note: I also disabled interactivePopGestureRecognizer because it was causing issues with the custom setup.
Swift 5+ (Back button with alert control)
override func viewDidLoad() {
super.viewDidLoad()
self.navigationItem.hidesBackButton = true
let newBackButton = UIBarButtonItem(title: "<Back", style: UIBarButtonItem.Style.plain, target: self, action: #selector(PGWebViewController.back(sender:)))
self.navigationItem.leftBarButtonItem = newBackButton
}
#objc func back(sender: UIBarButtonItem) {
let alert = UIAlertController(title: "Warning!", message: "Your payment process is not completed yet. Do you want to go back?", preferredStyle: .alert)
let ok = UIAlertAction(title: "OK", style: .default, handler: { action in
_ = self.navigationController?.popViewController(animated: true)
})
alert.addAction(ok)
let cancel = UIAlertAction(title: "Cancel", style: .default, handler: { action in
})
alert.addAction(cancel)
DispatchQueue.main.async(execute: {
self.present(alert, animated: true)
})}
You can simply remove unnecessary controllers from the stack, something like this:
self.navigationController?.viewControllers.removeAll(where: {
$0 is FirstViewController || $0 is SecondWithPinController
})