objective c - iOS Swift: UIPageViewController & API Calls in ContentViewControllers -

i've implemented uipageviewcontroller contains variable number of uiviewcontrollers each call api in viewdidload method.

i'm having few problems due "known issue" of viewcontrollerbeforeviewcontroller , viewcontrollerafterviewcontroller data source methods being called twice. e.g when swiping right, next , 1 after next view controllers initialised. in turn means each initialised view controller's api calls made.

i want next view controller initialised , hence 1 api call made. had thought moving api call viewwillappear although prefer if next view controller initialised.

is there way ensure data source methods called once?

thanks :)

func pageviewcontroller(pageviewcontroller: uipageviewcontroller, viewcontrollerafterviewcontroller viewcontroller: uiviewcontroller) -> uiviewcontroller? {      let currentindex = self.pages.indexof(viewcontroller as! locationviewcontroller)!     if currentindex == self.pages.count-1 {         return nil     }     let nextindex = currentindex + 1     return self.pages[nextindex]  }  func pageviewcontroller(pageviewcontroller: uipageviewcontroller, viewcontrollerbeforeviewcontroller viewcontroller: uiviewcontroller) -> uiviewcontroller? {      let currentindex = self.pages.indexof(viewcontroller as! locationviewcontroller)!     if currentindex == 0 {         return nil     }     let previousindex = currentindex - 1     return self.pages[previousindex]  }  func pageviewcontroller(pageviewcontroller: uipageviewcontroller, willtransitiontoviewcontrollers pendingviewcontrollers: [uiviewcontroller]) {     self.pendingindex = self.pages.indexof(pendingviewcontrollers.first! as! locationviewcontroller) }  func pageviewcontroller(pageviewcontroller: uipageviewcontroller, didfinishanimating finished: bool, previousviewcontrollers: [uiviewcontroller], transitioncompleted completed: bool) {     if completed {         self.currentindex = self.pendingindex         if let index = self.currentindex {             self.pagecontrol.currentpage = index         }     } }