sprite kit - how to get access to all my enemy nodes at the same time -

i have 6 sprites of enemies in spritekit game. want have access of them "enemies" in order make them appear on scene in random order. tried this:

class gamescene: skscene {  var redbox = skspritenode(imagenamed: "redbox") var greenbox = skspritenode(imagenamed: "greenbox") var bluebox = skspritenode(imagenamed: "bluebox") var magentabox = skspritenode(imagenamed: "magentabox") var cyanbox = skspritenode(imagenamed: "cyanbox") var yellowbox = skspritenode(imagenamed: "yellowbox")  func randombox() -> skspritenode {      let boxes = [redbox, greenbox, bluebox, magentabox, cyanbox, yellowbox]     let count = boxes.count     var randomone = int(arc4random_uniform(uint32(count)))     var randombox = boxes[randomone]      return randombox }  var onebox: skspritenode = randombox() } 

but in onebox xcode gives me error , says "missing parameter #1 in call".

how pick random node right way?

edit: code causing error:

class gamescene: skscene { //boxes var redbox = skspritenode(imagenamed: "redbox") var greenbox = skspritenode(imagenamed: "greenbox") var bluebox = skspritenode(imagenamed: "bluebox") var magentabox = skspritenode(imagenamed: "magentabox") var cyanbox = skspritenode(imagenamed: "cyanbox") var yellowbox = skspritenode(imagenamed: "yellowbox") var onebox:skspritenode!   func randombox() -> skspritenode {      let boxes = [redbox, greenbox, bluebox, magentabox, cyanbox, yellowbox]     let count = boxes.count     var randomone = int(arc4random_uniform(uint32(count)))     var randombox = boxes[randomone]      return randombox }  //random y func random() -> cgfloat {     return cgfloat(float(arc4random()) / 0xffffffff) }  func random(#min: cgfloat, max: cgfloat) -> cgfloat {     return random() * (max - min) + min }   override func didmovetoview(view: skview) {     /* setup scene here */      var onebox: skspritenode = randombox()      func addupperboxes() { let middley = random(min: size.height/2, max: size.height - size.height/3) onebox.position = cgpoint(x: size.width + onebox.size.width/2, y: middley) addchild(onebox) let middleduration = random(min: cgfloat(1.5), max: cgfloat(2.5))  let middlemove = skaction.moveto(cgpoint(x: -onebox.size.width/2, y: middley), duration: nstimeinterval(middleduration)) let middlemovedone = skaction.removefromparent() onebox.runaction(skaction.sequence([middlemove, middlemovedone]))     }      runaction(skaction.repeatactionforever(         skaction.sequence([             skaction.runblock(addupperboxes),             skaction.waitforduration(0.5)             ])         )) }