Randomizing node movement duration - swift

Question

I am making a game in SpriteKit and I have a node that is moving back and forth across the screen and repeating using the code:
let moveRight = SKAction.moveByX(frame.size.width/2.8, y: 0, duration: 1.5)
let moveLeft = SKAction.moveByX(-frame.size.width/2.8, y: 0, duration: 1.5)
let texRight = SKAction.setTexture(SKTexture(imageNamed: "Drake2"))
let texLeft = SKAction.setTexture(SKTexture(imageNamed: "Drake1"))
let moveBackAndForth = SKAction.repeatActionForever(SKAction.sequence([texRight, moveRight, texLeft, moveLeft,]))
Drake1.runAction(moveBackAndForth)
I am trying to figure out what method I can use to randomize the duration. Every time moveBackandForth runs, I want it to rerun using a different duration, (within games, not between). If someone could give me some example code to try I would really appreciate it.
Also arc4Random works fine, but it doesn't randomize within the game, only between games.

Answer 1

When you run actions like from your example and randomize duration parameter with something like arc4Random this is actually happening:
Random duration is set and stored in action.
Then action is reused in a sequence with a given duration.
Because the action is reused as it is, duration parameter remains the same over time and moving speed is not randomized.
One way to solve this (which I prefer personally) would be to create a "recursive action", or it is better to say, to create a method to run desired sequence and to call it recursively like this :
import SpriteKit
class GameScene: SKScene {
let shape = SKSpriteNode(color: UIColor.redColor(), size: CGSize(width: 20, height: 20))
override func didMoveToView(view: SKView) {
shape.position = CGPointMake(CGRectGetMidX(self.frame) , CGRectGetMidY(self.frame)+60 )
self.addChild(shape)
move()
}
func randomNumber() ->UInt32{
var time = arc4random_uniform(3) + 1
println(time)
return time
}
func move(){
let recursive = SKAction.sequence([
SKAction.moveByX(frame.size.width/2.8, y: 0, duration: NSTimeInterval(randomNumber())),
SKAction.moveByX(-frame.size.width/2.8, y: 0, duration: NSTimeInterval(randomNumber())),
SKAction.runBlock({self.move()})])
shape.runAction(recursive, withKey: "move")
}
}
To stop the action, you remove its key ("move").

Answer 2

I don't have any project where I can try right now.
But you might want to try this :
let action = [SKAction runBlock:^{
double randTime = 1.5; // do your arc4random here instead of fixed value
let moveRight = SKAction.moveByX(frame.size.width/2.8, y: 0, duration: randTime)
let moveLeft = SKAction.moveByX(-frame.size.width/2.8, y: 0, duration: randTime)
let texRight = SKAction.setTexture(SKTexture(imageNamed: "Drake2"))
let texLeft = SKAction.setTexture(SKTexture(imageNamed: "Drake1"))
let sequence = SKAction.sequence([texRight, moveRight, texLeft, moveLeft])
Drake1.runAction(sequence)
}]; 
let repeatAction = SKAction.repeatActionForever(action)
Drake1.runAction(repeatAction)
Let me know if it helped.