ios - How to get my UIPageViewController to load the correct index? Swift 3 -

this first post, open feedback if can improve question.

i have been studying swift year , trying build app uses uipageviewcontroller make app mimics experience of book. user able create many pages want. now, have template uiviewcontroller imageview , textview. user presses "+" button add next page, should appear pre-set blank imageview (that can set) , blank textview.

specs: i'm persisting user information coredata.

the problem: create new set of pages. add image , text. tap "+" , same on next page. when tap "+" after that, next page , each page after copies image , text previous page rather being empty page.

here logic how pages should run.

extension bookpageviewcontroller: uipageviewcontrollerdatasource {    func pageviewcontroller(_ pageviewcontroller: uipageviewcontroller, viewcontrollerbefore viewcontroller: uiviewcontroller) -> uiviewcontroller? {        guard let viewcontrollerindex = storypageviewcontrollers.index(of: viewcontroller as! templateviewcontroller) else { return nil }        if viewcontrollerindex == 0 { return nil } // page won't scroll below first page.        let previousindex = viewcontrollerindex - 1        guard storypageviewcontrollers.count > previousindex else { return nil }       currentpage = double(previousindex)        return storypageviewcontrollers[previousindex]   }    func pageviewcontroller(_ pageviewcontroller: uipageviewcontroller, viewcontrollerafter viewcontroller: uiviewcontroller) -> uiviewcontroller? {        guard let viewcontrollerindex = storypageviewcontrollers.index(of: viewcontroller as! templateviewcontroller) else { return nil }        let nextindex = viewcontrollerindex + 1       let storypageviewcontrollerscount = storypageviewcontrollers.count        guard storypageviewcontrollerscount != nextindex else { return nil }        guard storypageviewcontrollerscount > nextindex else { return nil }       currentpage = double(nextindex)       return storypageviewcontrollers[nextindex]   }    func presentationcount(for pageviewcontroller: uipageviewcontroller) -> int {       return storypageviewcontrollers.count   }      func presentationindex(for pageviewcontroller: uipageviewcontroller) -> int {       guard let firstviewcontroller = viewcontrollers?.first,           let firstviewcontrollerindex = storypageviewcontrollers.index(of: firstviewcontroller as! templateviewcontroller) else       { return 0 }        return firstviewcontrollerindex   } } 

this ibaction "+" button:

guard let book = book else { return } pagecontroller.shared.createpagewith(text: "", pagenumber: currentpage + 1.0, image: #imageliteral(resourcename: "imageviewplaceholder"), book: book)  updatestorypageviewcontrollers()  setviewcontrollers([storypageviewcontrollers[int(currentpage) + 1]], direction: .forward, animated: true, completion: nil) 

update: requested, here functions commenters asked for.

func updatestorypageviewcontrollers() {      // mark: - return here talk spencer fixing vc updating.      // make check see pages have view controllers, , make new view controller pages don't.      guard let book = book else { return }      // create array of view controllers store page vcs being instantiated     var temporaryviewcontrollers: [templateviewcontroller] = []      // loop through books pages, , make view controller each     if let pages = book.pages?.array as? [page], pages.count > 0 {         page in pages {              let storyboard = uistoryboard(name: "main", bundle: nil)             guard let pagevc = storyboard.instantiateviewcontroller(withidentifier: "templateviewcontroller") as? templateviewcontroller else { break }              pagevc.page = page             temporaryviewcontrollers.append(pagevc)         }     } else {          //fixme: - default image set here.         guard let page = pagecontroller.shared.createpagewith(text: "", pagenumber: 0, image: #imageliteral(resourcename: "imageviewplaceholder"), book: book) else { return }         let storyboard = uistoryboard(name: "main", bundle: nil)         guard let pagevc = storyboard.instantiateviewcontroller(withidentifier: "templateviewcontroller") as? templateviewcontroller else { return }         pagevc.page = page          temporaryviewcontrollers.append(pagevc)     }     // set self.storypageviewcontrollers array array made , filled.     self.storypageviewcontrollers = temporaryviewcontrollers } 

here code createpagewith method:

@discardableresult func createpagewith(text: string, pagenumber: double, image: uiimage, book: book) -> page? {     //turns uiimage data saved in coredata.     guard let data = uiimagejpegrepresentation(image, 0.8) else { return nil }      let page = page(text: text, pagenumber: pagenumber, photodata: data, book: book)      bookcontroller.shared.savetopersistentstore()      return page } 

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