ios - Why does SpriteKit crash when transitioning back and forth between scenes -

i checked answer here , on other sites didn't definitive solution.

i have 2 scenes

scene 1:

class gamemenuscene: skscene {  override func didmovetoview(view: skview) {      // add background     var background: skspritenode = skspritenode(imagenamed: "starfield")     background.position = cgpointmake(-20, 0)     background.size = cgsizemake(self.size.width + 40, self.size.height)     background.anchorpoint = cgpointzero     background.blendmode = skblendmode.replace     self.addchild(background)      // add game title     gametitle = skspritenode(imagenamed: "title")     gametitle.name = "game title"     gametitle.xscale = scale     gametitle.yscale = scale     gametitle.position = cgpoint(x: cgrectgetmidx(self.frame), y: self.frame.height * 0.75)     self.addchild(gametitle)      // add scoreboard     scoreboard = skspritenode(imagenamed: "scoreboard")     scoreboard.name = "scoreboard"     scoreboard.xscale = scale     scoreboard.yscale = scale     scoreboard.position = cgpoint(x: cgrectgetmidx(self.frame), y: self.frame.height * 0.50)     self.addchild(scoreboard)      // add play button     playbutton = skspritenode(imagenamed: "playbutton")     playbutton.name = "playbutton"     playbutton.xscale = scale     playbutton.yscale = scale     playbutton.position = cgpoint(x: cgrectgetmidx(self.frame), y: self.frame.height * 0.25)     self.addchild(playbutton)      // add menu score label     var menuscorelabel = sklabelnode()     menuscorelabel.fontname = fontname     menuscorelabel.fontsize = scorefontsize     menuscorelabel.text = string(score)     menuscorelabel.position = cgpointmake(scoreboard.position.x - (scoreboard.size.width / 4), scoreboard.position.y - (scoreboard.size.height / 4))     menuscorelabel.zposition = 10     self.addchild(menuscorelabel)      // add menu top score label     var menutopscorelabel = sklabelnode()     menutopscorelabel.fontname = fontname     menutopscorelabel.fontsize = scorefontsize     menutopscorelabel.text = string(userdefaults.integerforkey("topscore"))     menutopscorelabel.position = cgpointmake(scoreboard.position.x + (scoreboard.size.width / 4), scoreboard.position.y - (scoreboard.size.height / 4))     menutopscorelabel.zposition = 10     self.addchild(menutopscorelabel)  }  override func touchesbegan(touches: set<nsobject>, withevent event: uievent) {     /* called when touch begins */      touch in (touches as! set<uitouch>) {          // touch location         var touchlocation = touch.locationinnode(self)          // check if play button presssed          if playbutton.containspoint(touchlocation) == true {              //println("right node touched")              // transition gamescene.swift             var transition: sktransition = sktransition.fadewithduration(1)              // configure view.             let scene = gamescene()             let skview = self.view! skview             skview.showsfps = true             skview.showsnodecount = true              /* sprite kit applies additional optimizations improve rendering performance */             skview.ignoressiblingorder = true              /* set scale mode scale fit window */             scene.size = skview.bounds.size             scene.scalemode = .aspectfill              skview.presentscene(scene, transition: transition)          }     } } 

}

scene 2:

class gamescene: skscene, skphysicscontactdelegate {

override func didmovetoview(view: skview) {     /* setup scene here */      // add background     var background: skspritenode = skspritenode(imagenamed: "starfield")     background.position = cgpointmake(-20, 0)     background.size = cgsizemake(self.size.width + 40, self.size.height)     background.anchorpoint = cgpointzero     background.blendmode = skblendmode.replace     self.addchild(background)      // add mainlayer & labelholderlayer     self.addchild(mainlayer)     self.addchild(labelholderlayer)      // add cannon     cannon = skspritenode(imagenamed: "cannon")     cannon.name = "cannon"     cannon.position = cgpoint(x: cgrectgetmidx(self.frame), y: 0)     self.addchild(cannon)      // add score label     scorelabel.name = "score label"     scorelabel.fontname = fontname     scorelabel.fontsize = scorefontsize     scorelabel.text = string(score)     scorelabel.position = cgpointmake(cgrectgetmidx(self.frame), self.frame.size.height - scorefontsize)     scorelabel.zposition = 10     self.addchild(scorelabel)      // add livesdisplay     livesdisplay = skspritenode(imagenamed: "ammo5")     livesdisplay.name = "livesdisplay"     livesdisplay.position = cgpoint(x: self.size.width - livesdisplay.size.width, y: self.size.height - livesdisplay.size.height)     self.addchild(livesdisplay)      // settings new game     newgame()  }  func gameisover() {      // set game on flag , stop movement     gameover = 1     mainlayer.speed = 0     mainlayer.paused = true      // add game on label     gameoverlabel.fontname = fontname     gameoverlabel.fontsize = gameoverfontsize     gameoverlabel.text = "game over!"     gameoverlabel.position = cgpointmake(cgrectgetmidx(self.frame), cgrectgetmidy(self.frame))     gameoverlabel.zposition = 10     labelholderlayer.addchild(gameoverlabel)      // set main menu top score     if score > userdefaults.integerforkey("topscore") {          userdefaults.setinteger(score, forkey: "topscore")         userdefaults.synchronize()      }      // run acton sequence (wait few seconds before transitioning)     runaction(skaction.sequence([skaction.waitforduration(1), skaction.runblock({ () -> void in          // transition gamemenuscene         var transition: sktransition = sktransition.fadewithduration(1)          // configure view.         let scene = gamemenuscene()         let skview = self.view! skview         skview.showsfps = true         skview.showsnodecount = true          /* sprite kit applies additional optimizations improve rendering performance */         skview.ignoressiblingorder = true          /* set scale mode scale fit window */         scene.size = skview.bounds.size         scene.scalemode = .aspectfill          skview.presentscene(scene, transition: transition)      })]))  } 

}

when launch app, can transition scene 1 scene 2. when game over, app transitions scene 1. when try go scene 2 again, app crashes. happens on device, on simulator, can go , forth without problems.

the error sknode being added exists. know means , error starts when try

    // add mainlayer & labelholderlayer     self.addchild(mainlayer)     self.addchild(labelholderlayer) 

but don't see why can add background no problem crash there on. why work on simulator not on device? need check in didmovetoview if nodes created?

i found out mistake making.

i instantiating nodes outside scene 2 class, making them global. therefore when went scene 1 -> scene 2 -> scene 1 there not problem going scene 2 again caused crash because nodes globally created.

solution:

moving following code within class solved problem.

var mainlayer = skspritenode() var labelholderlayer = skspritenode() var livesdisplay = skspritenode() var scorelabel = sklabelnode()