Is there any equivalent in Swift to RACObserve(self, presentingViewController)?
Or any other why to imitate this behaviour?
My issue is that I want to be notified whenever a view controller is "hidden" by another view controller. In objc what I'd do is to check if self.presentingViewController is nil.
Note that in this scenario there's no knowledge of which view controller is presented, so it's impossible to notify from within its viewDidAppear/viewDidDisappear.
As I understand your question: you need to to know which view controller is presented now and you need notification inviewDidAppear/viewDidDisappear.
So we can get this in several way.
The simple way is:
Get information of which is the top ViewController right now.
2.Call this method in your viewDidAppear/viewDidDisappear
Like this :
Get Which is The Top ViewController
func getTopViewController() -> UIViewController? {
if var topVC = UIApplication.shared.keyWindow?.rootViewController {
while let presentedViewController = topVC.presentedViewController {
topVC = presentedViewController
return topVC
}
return topVC
}
return nil
}
Call in viewDidAppear:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(true)
if let top = getTopViewController() {
print("topView Controller name \(top.title)")
top.view.backgroundColor = .red
}
}
Hope it will help you !
Related
When we perform a segue, it is easy to get the destination view controller so we can pass data to it using the prepare(for:) method.
I'd like to know the correct way to do this when the back button of a navigation controller is pressed.
I've managed to piece together something that works, but it feels wrong to be using my knowledge of the hierarchy of the view controllers within the navigation controller rather than getting the destination dynamically. Maybe i'm overthinking it?
override func willMove(toParent parent: UIViewController?) {
super.willMove(toParent: parent)
// This method is called more than once - parent is only nil when back button is pressed
if (parent == nil) {
guard let destination = self.navigationController?.viewControllers.first as? MyTableViewController else {
return
}
print("destination is \(destination)")
// set delegate of my networking class to destination here
// call async method on networking class to retrieve updated data for my table view
}
}
As a general rule, trying to do that makes for too tight of a coupling. The VC you are navigating away from shouldn't need to know about where it's headed.
Probably better to implement your networking class methods in viewWillAppear or viewDidAppear inside your MyTableViewController class.
However, you could give this a try:
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
// make sure we're in a navigation controller
guard let navC = navigationController else { return }
if navC.viewControllers.firstIndex(of: self) != nil {
// we're still in the nav stack, so we've either
// pushed to another VC, or presented a full-screen VC
// (or maybe something else)
return
}
// we've been removed from the nav stack
// so user tapped Back button
print("back button tapped")
// see if we're navigating back to an instance of MyTableViewController
guard let destVC = navC.viewControllers.last as? MyTableViewController else {
return
}
// do something with destVC...
print("on our way to", destVC)
}
Note: I just did this as an example... it would need plenty of testing and possibly additional case handling.
assuming I have a viewcontroller (vcA) that pushes QRCodeScannerViewcontroller (vcB). When (vcB) scanned something, It will push ResultviewController (vcC).
-Those 3 views is connected to a UInavigation controller
-the user clicks on the back button on (vcC)
my question is:
1)how can I know if (vcB) is visible without changing code on (vcB)? (vcB) is a pod
2)where will I put this code? I can only access (vcA)
i tried adding this code on (vcA) but nothing happened
override func viewDidDisappear(_ animated: Bool) {
if (vcB.isViewLoaded && (vcB.view.window != nil)){
print("vcb did appear!")
}
}
To know if an instance of cvB's class exists in the navigation stack, you could use this piece of code:
let result = self.navigationController?.viewControllers.filter({
if let vcB = $0 as? UIViewController { // Replace UIViewController with your class, for example ViewControllerB
return true
}
return false
})
if result.isEmpty {
print("An instance of vcB's class hasn't been pused before")
} else {
print("An instance of vcB's class has been pused before")
}
I have a UICollectionViewCell class "ProductCell"; I am trying to access the current navigation controller in order to update a barbuttonicon. I have tried the following code as this is what I use in my other UIViewControllers:
let nav = self.navigationController as! MFNavigationController
nav.updateCartBadgeValue()
However it states that the
value of type ProductCell has no member navigationController
I am aware that this is not a UIViewController but surely you should be able to access the current navigation controller the same way?
I also know that you can access the navigation controller by using UIApplication in the following way:
let navigationController = application.windows[0].rootViewController as! UINavigationController
I am not sure if that is a good way of doing it though.
Any help is much appreciated
Thanks
UIResponder chain will help here.
You can search the responder chain to find the controller for any view
extension UIView {
func controller() -> UIViewController? {
if let nextViewControllerResponder = next as? UIViewController {
return nextViewControllerResponder
}
else if let nextViewResponder = next as? UIView {
return nextViewResponder.controller()
}
else {
return nil
}
}
func navigationController() -> UINavigationController? {
if let controller = controller() {
return controller.navigationController
}
else {
return nil
}
}
}
controller() will return the closest responder that is of type UIViewController
Then on the returned controller you just need to find its navigation controller. You can use navigationController() here.
The simplest way is to add a property to you cell class that weakly references a UINavigationController
weak var navigationController: UINavigationController?
you will need to assign it in your cellForRow(atIndexPath:_) method.
let cell = tableView.dequeueReusableCell(withIdentifier: "yourReuseID") as! YourCellClass
cell.navigationController = navigationController //will assign your viewController's navigation controller to the cell
return cell
Unless things change, this is a good way to do it. To give you an example of a messier solution... You could add a
let hostViewController:UIViewController
property to your cell and add an initializer to handle it
let cell = ProductCell(vc: self)
But I don't think that's a better way to do it. your suggestion works fine.
let navigationController = application.windows[0].rootViewController as! UINavigationController
I'm having the hardest time finding an answer for this.
I have a xib view that is within a scrollview that is within a view controller. In the xib I have a button with an action and I need to segue to a view controller I have in my storyboard. I also would like to be able to use a custom segue.
So far, I have read that I can instantiate the viewcontroller from the storyboard to segue to it. But then I don't know how to present that controller.
thanks for any help...
UPDATE:
this is the code I'm using to perform the segue.
In parent ViewController:
static var referenceVC: UIViewController?
override func viewDidLoad() {
super.viewDidLoad()
print("viewdidload")
LevelSelectViewController.referenceVC = self
setupScrollView()
}
code in xib view file
let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "sightWordController")
let parent = LevelSelectViewController.referenceVC!
let segue = InFromRightCustomSegue(identifier: "test", source: parent, destination: vc)
segue.perform()
As noted in the comments, Segues are typically confined to storyboard usage as noted in the documentation. You can implement a custom xib view in a storyboard via #IBDesignable like approaches and have you're view load from the xib into the storyboard file/class. This way, you gain the benefits of both worlds. Otherwise, you may want to approach this in another fashion (such as delegates/target-action events, etc).
You may also climb the responder chain and call a segue related to the VC loaded from the storyboard (the segue doesn't necessarily have to be attached to any particular action) via getting a reference to the VC and calling the segue. You can climb the responder chain in a manner such as the example code below:
protocol ChildViewControllerContainer {
var parentViewController: UIViewController? { get }
}
protocol ViewControllerTraversable {
func viewController<T: UIViewController>() -> T?
}
extension UIView: ViewControllerTraversable {
func viewController<T: UIViewController>() -> T? {
var responder = next
while let currentResponder = responder {
guard responder is T else {
responder = currentResponder.next
continue
}
break
}
return responder as? T
}
}
extension UITableViewCell: ChildViewControllerContainer {
weak var parentViewController: UIViewController? {
return viewController() as UIViewController?
}
}
I am getting "unexpectedly found nil while unwrapping an Optional value" because in my code below I am trying to assign value to webview before its initialize. I am trying to transition from Master to Detail view controller.
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "showDetail" {
if let indexPath = self.tableView.indexPathForSelectedRow() {
let object = self.fetchedResultsController.objectAtIndexPath(indexPath) as NSManagedObject
let controller = (segue.destinationViewController as UINavigationController).topViewController as DetailViewController
controller.detailItem = object
controller.navigationItem.leftBarButtonItem = self.splitViewController?.displayModeButtonItem()
controller.navigationItem.leftItemsSupplementBackButton = true
}
}
}
Detail View Code:
var detailItem: AnyObject? {
didSet {
// Update the view.
self.configureView()
}
}
func configureView() {
// Update the user interface for the detail item.
if let detailContent = detailItem?.valueForKey("content") as? String{
self.webView.loadHTMLString(detailContent as String, baseURL:nil)
}
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
self.configureView()
}
It is failing because my Webview in Nil. How do I come around this situation where my outlets are not initialized while setting them.
Please help.
Thanks.
Stop and think about the order in which things happen:
prepareForSegue - The destination view controller exists, but that's all. It has no view and its outlets have not been set. You can set its non-outlet properties but that's all you can do.
The segue starts to happen.
The destination view controller gets viewDidLoad. Now it has a view and its outlets are set.
The segue completes and the destination view controller gets viewWillAppear: and later, viewDidAppear:. Now its view is actually in the interface.
So clearly you cannot permit configureView to assume that the web view exists, because the first time it is called, namely in prepareForSegue, it doesn't exist. configureView needs to test explicitly whether self.webView is nil, and if it is, it should do nothing:
func configureView() {
// Update the user interface for the detail item.
if self.webView == nil { return } // no web view, bail out
if let detailContent = detailItem?.valueForKey("content") as? String{
self.webView.loadHTMLString(detailContent as String, baseURL:nil)
}
}
After that, everything will be fine. viewDidLoad will subsequently be called, and configureView will be called again - and this time, both detailItem and the web view exist, so all will be well.