ios - Swift: Fatal error: unexpectedly found nil while unwrapping an Optional value (SpriteKit) -


i've started learning program ios games spritekit , i'm novice programming (i have programmed in java , swift before this). started out doing tutorial found online. i'm @ point trying add "game over" scene, , keep getting error

"thread 1:exc-bad_instruction(code=exc_i386_invop,subcode=0x0)"

when declaring gameoverlabel constant. compiles crashes @ run time ball hits bottom of screen, supposed trigger 'game over' screen.

import spritekit  let gameoverlabelcategoryname = "gameoverlabel"  class gameoverscene: skscene {     var gamewon: bool = false {          didset {     let gameoverlabel = childnodewithname(gameoverlabelcategoryname) as! sklabelnode             gameoverlabel.text = gamewon ? "game won" : "game over"         } }     override func touchesbegan(touches: set<nsobject>, withevent event: uievent) {         if let view = view {             let gamescene = gamescene.unarchivefromfile("gamescene") as! gamescene             view.presentscene(gamescene)         }     } }

also if has suggestions of places can go learn more spritekit, articles or videos, appreciated things have found have been in objective-c , doing in swift.

here tutorial have been following..

childnodewithname return nil if node name not exist. code not checking possibility (the as! assumes both not nil , of appropriate type) causing crash.

the tutorial asks create 'gameoverlabel' node , name before creating code. check did correctly , did not misname (it case sensitive example).


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