iOS Swift: UIPageViewController - Turning page programmatically

Question

I have a UIPageViewController, which works fine when we swipe left or right to turn pages.

class ViewController: UIViewController, UIPageViewControllerDataSource {
...
}

Now I intend to provide Previous/Next button on the page too, so that pages can be turned by clicking on these buttons.

How can I trigger the swipe left/right behaviour OR turn pages programmatically?

---

Note

This is a question for Swift language, not Objective-C.

Answer 1

Use this funtion and set the transition style for the animation you want.

Answer 2

There's generally no need to fiddle around with page indexes and what not. Chances are you are already implementing a dataSource: UIPageViewControllerDataSource, which has all of what you need to get a previous or next ViewController to display.

Swift 2.2 Example:

extension UIPageViewController {

    func goToNextPage(){

        guard let currentViewController = self.viewControllers?.first else { return }

        guard let nextViewController = dataSource?.pageViewController( self, viewControllerAfterViewController: currentViewController ) else { return }

        setViewControllers([nextViewController], direction: .Forward, animated: false, completion: nil)

    }


    func goToPreviousPage(){

        guard let currentViewController = self.viewControllers?.first else { return }

        guard let previousViewController = dataSource?.pageViewController( self, viewControllerBeforeViewController: currentViewController ) else { return }

        setViewControllers([previousViewController], direction: .Reverse, animated: false, completion: nil)

    }

}

This way you're guaranteed that the pages you're transitioning to are exactly what the PageViewController's built in gestures would trigger.

Answer 3

The Swift 3 version of SuitedSloth's answer (with a small tweak to the animated parameter as I needed it to be animated by default, but still taking a parameter in the function) in case anyone needs it:

extension UIPageViewController {

    func goToNextPage(animated: Bool = true) {
        guard let currentViewController = self.viewControllers?.first else { return }
        guard let nextViewController = dataSource?.pageViewController(self, viewControllerAfter: currentViewController) else { return }
        setViewControllers([nextViewController], direction: .forward, animated: animated, completion: nil)
    }

    func goToPreviousPage(animated: Bool = true) {
        guard let currentViewController = self.viewControllers?.first else { return }
        guard let previousViewController = dataSource?.pageViewController(self, viewControllerBefore: currentViewController) else { return }
        setViewControllers([previousViewController], direction: .reverse, animated: animated, completion: nil)
    }

}

Answer 4

Here is the swift 4 implementation with the delegates as well.

Since I also use the UIPageViewControllerDelegate, and the delegate methods weren't called with most of the setViewController solutions.

Thanks to Andrew Duncan's for his comment about the delegate.

// Functions for clicking next and previous in the navbar, Updated for swift 4
@objc func toNextArticle(){
    guard let currentViewController = self.viewControllers?.first else { return }

    guard let nextViewController = dataSource?.pageViewController( self, viewControllerAfter: currentViewController ) else { return }

    // Has to be set like this, since else the delgates for the buttons won't work
    setViewControllers([nextViewController], direction: .forward, animated: true, completion: { completed in self.delegate?.pageViewController?(self, didFinishAnimating: true, previousViewControllers: [], transitionCompleted: completed) })
}

@objc func toPreviousArticle(){
    guard let currentViewController = self.viewControllers?.first else { return }

    guard let previousViewController = dataSource?.pageViewController( self, viewControllerBefore: currentViewController ) else { return }

    // Has to be set like this, since else the delgates for the buttons won't work
    setViewControllers([previousViewController], direction: .reverse, animated: true, completion:{ completed in self.delegate?.pageViewController?(self, didFinishAnimating: true, previousViewControllers: [], transitionCompleted: completed) })
}

Answer 5

Here is a swift implementation of this:

private func slideToPage(index: Int, completion: (() -> Void)?) {
    let count = //Function to get number of viewControllers
    if index < count {
        if index > currentPageIndex {
            if let vc = viewControllerAtIndex(index) {
                self.pageViewController.setViewControllers([vc], direction: UIPageViewControllerNavigationDirection.Forward, animated: true, completion: { (complete) -> Void in
                    self.currentPageIndex = index
                    completion?()
                })
            }
        } else if index < currentPageIndex {
            if let vc = viewControllerAtIndex(index) {
                self.pageViewController.setViewControllers([vc], direction: UIPageViewControllerNavigationDirection.Reverse, animated: true, completion: { (complete) -> Void in
                    self.currentPageIndex = index
                    completion?()
                })
            }
        }
    }
}

viewControllerAtIndex(index: Int) -> UIViewController? is my own function to get the correct view controller to swipe to.

Answer 6

Just leaving this out here incase any one wants to use a defined protocol to navigate around and change view controllers programatically.

@objc protocol AppWalkThroughDelegate {
  @objc optional func goNextPage(forwardTo position: Int)
  @objc optional func goPreviousPage(fowardTo position: Int)
}

Use the above protocol and confirm to root UIPageViewController to manage navigation between view controllers.

Example below:

class AppWalkThroughViewController: UIPageViewController, UIPageViewControllerDataSource, AppWalkThroughDelegate {

    // Add list of view controllers you want to load

    var viewControllerList : [UIViewControllers] = {
       let firstViewController = FirstViewController()
       let secondViewController = SecondViewController() 
       // Assign root view controller as first responder
       secondViewController.delegate = self  

       let thirdViewController = ThirdViewController() 

    }

    override func viewDidLoad() {
       super.viewDidLoad()
       self.dataSource = self
    }

    // Navigate to next page 
    func goNextPage(fowardTo position: Int) {
       let viewController = self.viewControllerList[position]
       setViewControllers([viewController], direction: 
       UIPageViewControllerNavigationDirection.forward, animated: true, completion: nil)
    }

    }

Once achieved all that, child view controllers that need to make UIPageViewController move to next or previous page can use AppWalkThroughDelegate methods by passing a specific number onto delegate property.

Example below: Delegate method invoked once button pressed

    class SecondViewController: UIViewController {

        var delegate: AppWalkThroughDelegate!

        override func viewDidLoad() {
           super.viewDidLoad()
           self.dataSource = self
        }

         @IBAction func goNextPage(_ sender: Any) {
            // Can be any number but not outside viewControllerList bounds 
            delegate.goNextPage!(fowardTo: 2)
         }
    }