ios - uipageviewcontroller disable right swipe -

i have uipageviewcontroller 4 individual view controllers in it. want disable right swipe action first view controller , disable left swipe action fourth view controller. when app launches, want user able swipe left , not right, because swiping right, takes user fourth view controller , swiping left on fourth view controller takes user first view controller. here code.

class tutorialpageviewcontroller: uipageviewcontroller, uipageviewcontrollerdatasource, uipageviewcontrollerdelegate {     weak var tutorialdelegate: tutorialpageviewcontrollerdelegate?      lazy var vcarr: [uiviewcontroller] = {         return [self.vcinstance(name: "firstvc"),                 self.vcinstance(name: "secondvc"),                 self.vcinstance(name: "thirdvc"),                 self.vcinstance(name: "fourthvc")]      }()      private func vcinstance(name: string) -> uiviewcontroller {         return uistoryboard(name: "main", bundle: nil).instantiateviewcontroller(withidentifier: name)     }      override func viewdidload() {         super.viewdidload()          let pagecontrol = uipagecontrol.appearance()         //customizing         pagecontrol.pageindicatortintcolor = uicolor.lightgray         pagecontrol.currentpageindicatortintcolor = uicolor(red:0.23, green:0.73, blue:1.00, alpha:1.0)          datasource = self         delegate = self         self.datasource = self         self.delegate = self          if let firstvc = vcarr.first {             setviewcontrollers([firstvc], direction: .forward, animated: true, completion: nil)             tutorialdelegate?.tutorialpageviewcontroller(tutorialpageviewcontroller: self, didupdatepagecount: vcarr.count)          }     }     override func viewdidlayoutsubviews() {         super.viewdidlayoutsubviews()          view in self.view.subviews {             if view uiscrollview {                 view.frame = uiscreen.main.bounds             } else if view uipagecontrol {                 view.backgroundcolor = uicolor.clear             }         }     }      public func pageviewcontroller(_ pageviewcontroller: uipageviewcontroller, viewcontrollerbefore viewcontroller: uiviewcontroller) -> uiviewcontroller? {         guard let viewcontrollerindex = vcarr.index(of: viewcontroller) else {             return nil         }          let previousindex = viewcontrollerindex - 1          guard previousindex >= 0 else {             return vcarr.last         }          guard vcarr.count > previousindex else {             return nil         }         return vcarr[previousindex]     }      public func pageviewcontroller(_ pageviewcontroller: uipageviewcontroller, viewcontrollerafter viewcontroller: uiviewcontroller) -> uiviewcontroller? {         guard let viewcontrollerindex = vcarr.index(of: viewcontroller) else {             return nil         }          let nextindex = viewcontrollerindex + 1          guard nextindex < vcarr.count else {             return vcarr.first         }          guard vcarr.count > nextindex else {             return nil         }         return vcarr[nextindex]     }      public func presentationcount(for pageviewcontroller: uipageviewcontroller) -> int {         return vcarr.count     }       public func presentationindex(for pageviewcontroller: uipageviewcontroller) -> int {         guard let firstviewcontroller = viewcontrollers?.first,         let firstviewcontrollerindex = vcarr.index(of: firstviewcontroller) else {              return 0          }          return firstviewcontrollerindex      } }  extension tutorialpageviewcontroller {      func pageviewcontroller(pageviewcontroller: uipageviewcontroller,                             didfinishanimating finished: bool,                             previousviewcontrollers: [uiviewcontroller],                             transitioncompleted completed: bool) {         if let firstviewcontroller = viewcontrollers?.first,             let index = vcarr.index(of: firstviewcontroller) {             tutorialdelegate?.tutorialpageviewcontroller(tutorialpageviewcontroller: self, didupdatepageindex: index)         }     }  } 

basically need change following lines

guard previousindex >= 0 else {             return nil         }   guard nextindex < vcarr.count else {             return nil         } 

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change viewcontrollerafter as

 public func pageviewcontroller(_ pageviewcontroller: uipageviewcontroller, viewcontrollerafter viewcontroller: uiviewcontroller) -> uiviewcontroller? {             guard let viewcontrollerindex = vcarr.index(of: viewcontroller) else {                 return nil             }              let nextindex = viewcontrollerindex + 1              guard nextindex < vcarr.count else {             return nil         }              guard vcarr.count > nextindex else {                 return nil             }              return vcarr[nextindex]         } 

change viewcontrollerbefore as

public func pageviewcontroller(_ pageviewcontroller: uipageviewcontroller, viewcontrollerbefore viewcontroller: uiviewcontroller) -> uiviewcontroller? {         guard let viewcontrollerindex = vcarr.index(of: viewcontroller) else {             return nil         }          let previousindex = viewcontrollerindex - 1         guard previousindex >= 0 else {             return nil         }         guard vcarr.count > previousindex else {             return nil         }         return vcarr[previousindex]     }