ios - UITableView with UIPanGestureRecognizer causes "jumping" touch -

the case: https://github.com/artworkad/ios_jumping_y.git

the container

class containercontroller: uiviewcontroller {      @iboutlet weak var container: uiview!        @iboutlet weak var foregroundtopspace: nslayoutconstraint!     @iboutlet weak var foregroundbottomspace: nslayoutconstraint! } 

the container connected uitableviewcontroller right.

what want do

the user scrolls table , when reaches top want move table down same movement. change top/bottom space of container view. causes table jump.

class maincontroller: uitableviewcontroller, uigesturerecognizerdelegate {      var panrecognizer: uipangesturerecognizer!      var gotstart: bool = true      var starttouch: cgpoint!      override func viewdidload() {         super.viewdidload()          self.tableview.bounces = false          self.panrecognizer = self.tableview.pangesturerecognizer         self.panrecognizer.addtarget(self, action: "pan:")         self.tableview.addgesturerecognizer(self.panrecognizer)     }      func gesturerecognizer(gesturerecognizer: uigesturerecognizer, shouldrecognizesimultaneouslywithgesturerecognizer othergesturerecognizer: uigesturerecognizer) -> bool {         return true     }      func pan(rec:uipangesturerecognizer){          if let parent = self.parentviewcontroller as? containercontroller {              var y = self.tableview.contentoffset.y             var touch = rec.locationinview(self.view)              // jumping y             println(touch.y)              if y == -64 {                  if self.gotstart  || y < -64 || y > -64 {                      self.starttouch = touch                     self.gotstart = false                  } else {                      if rec.state == .changed {                          var changedverticalheight = (self.starttouch.y - touch.y)*(-1)                          if changedverticalheight <= parent.view.frame.size.height && touch.y >= changedverticalheight {                              parent.foregroundtopspace.constant = changedverticalheight                             parent.foregroundbottomspace.constant = -changedverticalheight                         }                      } else if rec.state == .ended {                          parent.foregroundtopspace.constant = 0                         parent.foregroundbottomspace.constant = 0                          self.gotstart = true                     }                 }             }         }     } } 

result:

any ideas whats wrong? there has problem container view because when move table view directly there no jumping.

i going clarify things in answer before put complete code

1. you can use function scrollviewwillenddragging know contentoffset going to, see below code :

   override func scrollviewwillenddragging(scrollview: uiscrollview, withvelocity velocity: cgpoint, targetcontentoffset: unsafemutablepointer<cgpoint>) {    println(targetcontentoffset.memory.y)         } 

2. you can use function scrollviewdidenddecelerating know when scroll has finished it.

then can merge 2 above tips accomplish goal in following way:

class maincontroller: uitableviewcontroller {     var position : cgfloat!     override func viewdidload() {       super.viewdidload()           }     override func scrollviewwillenddragging(scrollview: uiscrollview, withvelocity velocity: cgpoint, targetcontentoffset: unsafemutablepointer<cgpoint>) {         // save contentoffset go               position = targetcontentoffset.memory.y    }        override func scrollviewdidenddecelerating(scrollview: uiscrollview) {         // if reach top or more top when user move scroll        if (position < 0) {                           var = scrollview.contentoffset.y + 213            scrollview.setcontentoffset(cgpoint(x: 0, y: to), animated: true)        }            }         // default table stuff, not related problem       /* here comes rest of code of tableview */     } 

i remove code project relative pangesturerecognizer , bounces test.

in line var = scrollview.contentoffset.y + 213 can add position variable or value want, put 213 test down movement.

i hope you.