I don't understand how indexOfVC returns an index: the dataObject is an optional in the ContentViewController :
class ContentViewController : UIViewController {
var dataObject:AnyObject?
, and when we invoke indexOfVC, pageContent contains html strings. How the dataObject can be found in pageContent if dataObject is empty, and pageContent is filled with html text ?
func viewControllerAtIndex(index:Int)->ContentViewController?{
if (index < 0) || (index >= pageContent.count){
return nil
}
let storyboard = UIStoryboard(name: "Main", bundle: NSBundle.mainBundle())
var vc = storyboard.instantiateViewControllerWithIdentifier("ContentViewController") as ContentViewController
vc.dataObject = pageContent[index]
return vc
}
/* HERE */
func indexOfVC(viewController:ContentViewController) ->Int {
if let dataObject : AnyObject = viewController.dataObject {
return pageContent.indexOfObject(dataObject)
}
else {
return NSNotFound
}
}
func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
var index : Int = indexOfVC(viewController as ContentViewController)
println("after: index: \(index)") //found 0, then 1, 2,... when scrolling right
if (index == NSNotFound) {
return nil
}
index++
return viewControllerAtIndex(index)
}
//called in viewdidload
func createContentPages(){
var pageStrings = [String]()
for i in 1...11 {
pageStrings.append(String("<html><head></head><body><br><h1>Chapter \(i)</h1><p>This is the page \(i) of content displayed using UIPageViewController in iOS 8.</p></body></html>"))
}
pageContent = pageStrings
}
The code is from : http://www.techotopia.com/index.php/An_Example_Swift_iOS_8_UIPageViewController_Application
The answer is that dataObject is never nil at the time that indexOfVC is called. Although it is optional, and will be nil when the ContentViewController is first initialised, as soon as the viewControllerAtIndex method creates a ContentViewController, it sets its dataObject to one of the elements of the pageContent array:
var vc = storyboard.instantiateViewControllerWithIdentifier("ContentViewController") as ContentViewController
vc.dataObject = pageContent[index]
So the overall flow is:
The starting page is set in the viewDidLoad of the main view controller:
let startingViewController: ContentViewController = viewControllerAtIndex(0)!
This creates a VC and sets its dataObject to pageContent[0].
If you then swipe, the pageViewController will call viewControllerAfterViewControler:viewController. In this call, the viewController argument is the current view controller. The method needs to know the index of the current VC, so it calls indexOfVC with viewController as the argument.
indexOfVC reads the dataObject value for that view controller, which is pageContent[0]. Hence pageContent.indexOfObject(dataObject) returns the integer 0.
This is then incremented (index++) and so the call to viewControllerAtIndex will create a new VC for index 1. This will create a new view controller and immediately set its dataObject to pageContent[1]. And the cycle continues...
So as currently coded, indexOfVC is never passed a viewController where its dataObject is nil. But if it ever were, it would return the special value NSNotFound. Then viewControllerAfterViewController: checks the return value and, if it is NSNotFound, returns nil - which tells the page view controller not to permit the swipe.
Related
I've made a simple weather app as a side project (I'm not a software engineer) that shows temperatures in Fahrenheit and Celsius at the same time. The user can swipe horizontally between cities:
I've achieved this by using the multi-page app template that was available in Xcode as a new app template up until Xcode 9. When building the app up until Xcode 10, the problem was that when the user added a city to the array of cities, pages for newly added cities would not render if the user was on the last page of the carousel at the time of adding a new city. Even if so, when the user swiped left and then back right, the newly added cities would show up. Now, in Xcode 11, new view controllers for newly added cities never render, unless the user relaunches the app. That's a pretty big issue I'd like to fix.
I need help in figuring out how new view controllers can be rendered on demand into the existing multi-page carousel after addCity is called, even if the user is currently on the last page and w/o requiring an app restart.
Below is the full code that drives that multi-page carousel. Apologies some of the hacky stuff in there. For context, I'm a non-technical product manager trying to make some iOS apps as side projects.
import UIKit
import StoreKit
/*
A controller object that manages a simple model
The controller serves as the data source for the page view controller; it therefore implements pageViewController:viewControllerBeforeViewController: and pageViewController:viewControllerAfterViewController:.
It also implements a custom method, viewControllerAtIndex: which is useful in the implementation of the data source methods, and in the initial configuration of the application.
There is no need to actually create view controllers for each page in advance -- indeed doing so incurs unnecessary overhead. Given the data model, these methods create, configure, and return a new view controller on demand.
*/
class ModelController: NSObject, UIPageViewControllerDataSource {
var rootViewController = RootViewController()
var cities = [""]
let defaults = UserDefaults.standard
let currentCount = UserDefaults.standard.integer(forKey: "launchCount")
var pageViewController: UIPageViewController?
override init() {
super.init()
self.cities = self.defaults.stringArray(forKey: "SavedStringArray") ?? [String]()
if self.cities == [""] || self.cities.count == 0 {
self.cities = ["Current Location", "San Francisco", "New York"]
}
}
func addCity(name:String) {
self.cities.append(name)
self.defaults.set(self.cities, forKey: "SavedStringArray")
}
func viewControllerAtIndex(_ index: Int, storyboard: UIStoryboard) -> DataViewController? {
// Return the data view controller for the given index.
if (self.cities.count == 0) || (index >= self.cities.count) {
return nil
}
// Create a new view controller and pass suitable data.
let dataViewController = storyboard.instantiateViewController(withIdentifier: "DataViewController") as! DataViewController
//get city name
dataViewController.dataObject = self.cities[index]
return dataViewController
}
func indexOfViewController(_ viewController: DataViewController) -> Int {
// Return the index of the given data view controller.
// For simplicity, this implementation uses a static array of model objects and the view controller stores the model object; you can therefore use the model object to identify the index.
return self.cities.firstIndex(of: viewController.dataObject) ?? NSNotFound
}
// MARK: - Page View Controller Data Source
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
var index = self.indexOfViewController(viewController as! DataViewController)
if (index == 0) || (index == NSNotFound) {
return nil
}
index -= 1
return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
var index = self.indexOfViewController(viewController as! DataViewController)
if index == NSNotFound {
return nil
}
index += 1
if index == self.cities.count {
return nil
}
if index > 1 && currentCount > 2 {
print ("request review")
SKStoreReviewController.requestReview()
}
return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
}
}
Well I see some syntax in the following function which returns the topMostViewController. This function is defined in AppDelegate
func topViewController(controller: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
if let navigationController = controller as? UINavigationController {
//***A topViewController which is Returning itself
//***This is where I got Confusion
return topViewController(controller: navigationController.visibleViewController)
} else if let tabController = controller as? UITabBarController {
if let selected = tabController.selectedViewController {
return topViewController(controller: selected)
}
} else if let presented = controller?.presentedViewController {
return topViewController(controller: presented)
}
return controller
}
And it's used as
if (self.topViewController() as? SomeViewController) != nil {
if orientation.isPortrait {
return .portrait
} else {
return .landscape
}
}
I understood that the code is trying to set orientation based on the currently visible View Controller but I don't understand what is the necessity of returning the same function itself in topViewController. Also I see some syntax like
extension UIApplication {
/// The top most view controller
static var topMostViewController: UIViewController? {
return UIApplication.shared.keyWindow?.rootViewController?.visibleViewController
}
}
extension UIViewController {
/// The visible view controller from a given view controller
var visibleViewController: UIViewController? {
if let navigationController = self as? UINavigationController {
// *** Here it's returning Same variable i.e visibleViewController
// *** a function could call itself recursively. But how can a Variable calls itself recursively?
return navigationController.topViewController?.visibleViewController
} else if let tabBarController = self as? UITabBarController {
return tabBarController.selectedViewController?.visibleViewController
} else if let presentedViewController = presentedViewController {
return presentedViewController.visibleViewController
} else {
return self
}
}
}
Edited
That is called recursion. There is a condition in the recursion that cause t end the cycle :
Not in the navigationController, because it has another visible controller
Not in the tabBarController, because it has another visible controller
Not presenting another controller, because the presented one is visible
if one of these appears -> we go down one level and call this function again until none of these true.
It is a recursive function. The topViewController function calls itself to find the top most controller which is visible. The function will exit when controller?.presentedViewController returns nil (Which means that the value held by controller is the top most visible controller). You can also achieve the same without a recursive function as mentioned here: How to find topmost view controller on iOS, but it looks much more cleaner than the looping implementation.
I'm working on a quote app, I want the pages, except the first one, to be randomized. I don't want people opening the app to see the same initial quotes over and over again. If you could respond with edit to the code I would really appreciate it. Thank you in advance!
import UIKit
class ModelController: NSObject, UIPageViewControllerDataSource {
let pageData:NSArray = ["All quotes are from Kanye West, Enjoy!", "I refuse to accept other people's ideas of happiness for me. As if there's a 'one size fits all' standard for happiness","I am the greatest","I still think I'm the greatest.","They say you can rap about anything except for Jesus, that means guns, sex, lies, video tapes, but if I talk about God my record won't get played Huh?"]
override init() {
super.init()
}
func viewControllerAtIndex(_ index: Int, storyboard: UIStoryboard) -> DataViewController? {
// Return the data view controller for the given index.
if (self.pageData.count == 0) || (index >= self.pageData.count) {
return nil
}
// Create a new view controller and pass suitable data.
let dataViewController = storyboard.instantiateViewController(withIdentifier: "DataViewController") as! DataViewController
dataViewController.dataObject = self.pageData[index] as! String
return dataViewController
}
func indexOfViewController(_ viewController: DataViewController) -> Int {
// Return the index of the given data view controller.
// For simplicity, this implementation uses a static array of model objects and the view controller stores the model object; you can therefore use the model object to identify the index.
return pageData.index(of: viewController.dataObject)
}
// MARK: - Page View Controller Data Source
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
var index = self.indexOfViewController(viewController as! DataViewController)
if (index == 0) || (index == NSNotFound) {
return nil
}
index -= 1
return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
var index = self.indexOfViewController(viewController as! DataViewController)
if index == NSNotFound {
return nil
}
index += 1
if index == self.pageData.count {
return nil
}
return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
You can randomise your quote array and pass on the randomised array.
Checkout these link:
How do I shuffle an array in Swift? and
Shuffle array swift 3
I am trying to compare to UIViewController in Swift 3 but there is some error
extension UINavigationController
{
func myPopToViewController(viewController:UIViewController, animated:Bool) -> UIViewController? {
var arrViewControllers:[UIViewController] = []
arrViewControllers = self.viewControllers
for vc:UIViewController in arrViewControllers {
if(vc.isKind(of: viewController) ) // This Line gives me error
{
return (self.navigationController?.popToViewController(vc, animated: animated)?.last)!
}
}
return nil
}
}
/Users/varunnaharia/Documents/Projects/appname/appname/Public/UINavigationController+Extra.swift:18:30: Cannot convert value of type 'UIViewController' to expected argument type 'AnyClass' (aka 'AnyObject.Type')
and if try to use
if(vc is viewController)
It gives
/Users/varunnaharia/Documents/Projects/appname/appname/Public/UINavigationController+Extra.swift:18:22: Use of undeclared type 'viewController'
I am calling it through this
self.navigationController?.popOrPopToViewController(viewController: MyUIViewController(), animated: false)
for viewsController in arrViewControllers
{
if(viewsController.isKind(of: YourControllerClassName.self)){
}
}
Swift 4
Hope it will work for you
extension UINavigationController {
func myPopToViewController(viewController:UIViewController, animated:Bool) {
var arrViewControllers:[UIViewController] = []
arrViewControllers = self.viewControllers
for vc:UIViewController in arrViewControllers {
if(vc.isKind(of: viewController.classForCoder)){
(self.popToViewController(vc, animated: animated))
}
}
}
}
In swift, we use is instead of isKind(of:).
is is used to check the type of the object.
So you can use,
if(vc is UIViewController)
But I think here you are trying to match the 2 references of UIViewController.
So, you need to use === instead of is. This operator is used to match 2 references of same type.
if(vc === viewController)
If you want to compare to a particular view controller you have to compare their refererences.
Try this...
if(vc === viewController) )
{
return (self.navigationController?.popToViewController(vc, animated: animated)?.last)!
}
i just modify the answer of Mr. #BangOperator for move to particular View controller.
extension UINavigationController {
func popTo(controllerToPop:UIViewController) {
//1. get all View Controllers from Navigation Controller
let controllersArray = self.viewControllers
//2. check whether that view controller is exist in the Navigation Controller
let objContain: Bool = controllersArray.contains(where: { $0 == controllerToPop })
//3. if true then move to that particular controller
if objContain {
self.popToViewController(controllerToPop, animated: true)
}
}
}
This is what I posted as a possible solution to Traverse view controller hierarchy in Swift (slightly modified):
extension UIViewController {
func traverseAndFindClass<T where T : UIViewController>(T.Type) -> T? {
var currentVC = self
while let parentVC = currentVC.parentViewController {
println("comparing \(parentVC) to \(T.description())")
if let result = parentVC as? T { // (XXX)
return result
}
currentVC = parentVC
}
return nil
}
}
The method should traverse up the parent view controller hierarchy and return the first
instance of the given class, or nil if none is found.
But it does not work, and I cannot figure out why. The optional binding
marked with (XXX) always succeeds, so that the first parent view controller is returned
even if it is not an instance of T.
This can easily be reproduced: Create a project from the "iOS Master-Detail Application"
template in Xcode 6 GM, and add the following code to viewDidLoad() of the
MasterViewController class:
if let vc = self.traverseAndFindClass(UICollectionViewController.self) {
println("found: \(vc)")
} else {
println("not found")
}
self is a MasterViewController (a subclass of UITableViewController), and its
parent view controller is a UINavigationController.
There is no UICollectionViewController in the parent view
controllers hierarchy, so I would expect that the method
returns nil and the output is "not found".
But this is what happens:
comparing <UINavigationController: 0x7fbc00c4de10> to UICollectionViewController
found: <UINavigationController: 0x7fbc00c4de10>
This is obviously wrong, because UINavigationController is not a subclass of
UICollectionViewController. Perhaps I made some stupid error, but I could not find it.
In order to isolate the problem, I also tried to reproduce it with my own class
hierarchy, independent of UIKit:
class BaseClass : NSObject {
var parentViewController : BaseClass?
}
class FirstSubClass : BaseClass { }
class SecondSubClass : BaseClass { }
extension BaseClass {
func traverseAndFindClass<T where T : BaseClass>(T.Type) -> T? {
var currentVC = self
while let parentVC = currentVC.parentViewController {
println("comparing \(parentVC) to \(T.description())")
if let result = parentVC as? T { // (XXX)
return result
}
currentVC = parentVC
}
return nil
}
}
let base = BaseClass()
base.parentViewController = FirstSubClass()
if let result = base.traverseAndFindClass(SecondSubClass.self) {
println("found: \(result)")
} else {
println("not found")
}
And guess what? Now it works as expected! The output is
comparing <MyApp.FirstSubClass: 0x7fff38f78c40> to MyApp.SecondSubClass
not found
UPDATE:
Removing the type constraint in the generic method
func traverseAndFindClass<T>(T.Type) -> T?
as suggested by #POB in a comment makes it work as expected.
Replacing the optional binding by a "two-step binding"
if let result = parentVC as Any as? T { // (XXX)
as suggested by #vacawama in his answer also makes it work as expected.
Changing the build configuration from "Debug" to "Release" also makes the
method work as expected. (I have tested this only in the iOS Simulator so far.)
The last point could indicate that this is a Swift compiler or runtime bug. And I still
cannot see why the problem occurs with subclasses of UIViewController, but not
with subclasses of my BaseClass. Therefore I will keep the question open for a
while before accepting an answer.
UPDATE 2: This has been fixed as of Xcode 7.
With the final Xcode 7
release the problem does not occur anymore. The optional binding
if let result = parentVC as? T in the traverseAndFindClass() method
now works (and fails) as expected, both in Release and Debug configuration.
If you try to conditionally cast an object of type UINavigationController to a UICollectionViewController in a Playground:
var nc = UINavigationController()
if let vc = nc as? UICollectionViewController {
println("Yes")
} else {
println("No")
}
You get this error:
Playground execution failed: :33:16: error: 'UICollectionViewController' is not a subtype of 'UINavigationController'
if let vc = nc as? UICollectionViewController {
but if instead you do:
var nc = UINavigationController()
if let vc = (nc as Any) as? UICollectionViewController {
println("Yes")
} else {
println("No")
}
it prints "No".
So I suggest trying:
extension UIViewController {
func traverseAndFindClass<T where T : UIViewController>(T.Type) -> T? {
var currentVC = self
while let parentVC = currentVC.parentViewController {
println("comparing \(parentVC) to \(T.description())")
if let result = (parentVC as Any) as? T { // (XXX)
return result
}
currentVC = parentVC
}
return nil
}
}